Multiwavelength Astronomy Glossary

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a priori: Knowledge that is based on theory rather than observation or experience.

absolute zero: Temperature is a measurement of the how fast molecules are moving. At absolute zero, there is no movement of molecules. Absolute zero is 0 degrees Kelvin, -459.67 degrees Fahrenheit, or -273.15 degrees Celsius.

accretion disk: A relatively flat sheet of gas and dust surrounding a newborn star, a black hole, or any massive object growing in size by attracting material.

active galactic nuclei (AGN): A class of galaxies that spew massive amounts of energy from their centers, far more than ordinary galaxies. Many astronomers believe supermassive black holes may lie at the center of these galaxies and power their explosive energy output.

adaptive optics: A technique that compensates for atmospheric turbulence by quickly adjusting the light path in the optics. This removes seeing effects and enables the telescope to achieve much better resolution, closer to its theoretical resolving power.

Aerobee: A small rocket built by Aerojet General in the 1940s and 1950s. Aerobees were used for high atmospheric and cosmic radiation research and could carry payloads to approximately 230 km above Earth.

afterglow: Outflows of gamma-ray bursts decrease in temperature over a matter of hours. The resulting spectra are cooler and cooler.  As the temperature cools the photons are at longer and longer wavelengths; the objects become redder and redder and are referred to as afterglows, effectively the red afterglow of the hot, blue explosion like the morning-after embers of a campfire.

Air Force Cambridge Research Laboratory: The United States Air Force created the Air Force Cambridge Research Laboratories at Hanscom Air Force Base in Massachusetts. A series of rocket flights by the laboratory provided the first infrared all sky map.

Albertina University of Königsberg (Albertus University): A Protestant academy in Königsberg, Prussia that was founded in 1544. In 1945 the city of Königsberg was transferred to the Soviet Union according to the Potsdam Agreement and the university was closed.

algebraic geometry: A branch of mathematics that studies solutions to algebraic equations.

alpha particle: Alpha particles are helium nuclei, consisting of 2 protons and 2 neutrons.

alpha radiation (α): The radioactive decay of heavy nuclei by emission of an alpha particle, a nucleus of helium.

Alvarez, Luis (1911-1988): Luis Alvarez was an American experimental physicist and inventor, who spent most of his professional career at the Radiation Laboratory of the University of California, Berkeley. During World War II, Alvarez designed important radar systems for use by the military; and while at Los Alamos Laboratory, he developed the detonators for setting off the plutonium bomb. He flew as a scientific observer at both the Almagordo and Hiroshima explosions.  Alvarez was awarded the Nobel Prize in Physics in 1968 for his contributions to elementary particle physics.

American Astronomical Society: The American Astronomical Society is a professional organization of astronomers in North American whose mission is to enhance and share scientific understanding of the Universe.

American Science and Engineering (AS&E): An American company that was formed in 1958. In it’s early days it developed instruments for NASA. Riccardo Giaconni joined AS&E in 1959 and led a team of scientists who made many breakthroughs in X-ray astronomy.

angstrom: A unit of length equal to 0.00000001 centimeters. This may also be written as 1 x 10-8 cm or Å.

angular resolution: A measure of the angular size of the smallest object that can be distinguished by a telescope.

Annis, Martin: The founder of American Science & Engineering (AS&E). He founded AS&E in 1958 with the help of George Clark.

anode: The positive pole of any electron emitter, such as an electron tube or an electric cell. The negative pole or electrode is called a cathode.

Apache Point Observatory: Apache Point is an astronomical Observatory located in the Sacramento Mountains in New Mexico. It is home to four telescopes.

aperture: An opening or hole on an optical instrument which light passes through.

Apollo 11: The first NASA spaceflight that landed humans on the Moon. Apollo 11 was launched on July 16, 1969 and it landed on the Moon four days later, on July 20. The three members of the Apollo 11 crew were Neil Armstrong, Buzz Aldrin and Michael Collins.

Apollo Program: The Apollo program was NASA’s third human space flight program. Between the years of 1966 and 1972, the Apollo program launched 17 missions with the goal of putting a man on the Moon and returning him safely to Earth. In 1969, the goal was realized with the Apollo 11 mission. Five more missions had successful lunar landings and returns. During the missions, lunar rocks and soil samples were collected and returned to Earth for study.

arcminute: An angular measurement equal to 1/60th of a degree.

arcsecond: An angular measurement equal to 1/60th of an arcminute.

Argonne National Laboratory: Argonne National Laboratory is a United States Department of Energy (DOE) research laboratory in Argonne, IL. Argonne conducts basic research, technology development and prototype development and testing. The lab was started in 1942 when Enrico Fermi’s nuclear reaction experiments were moved out of Chicago due to the danger they posed to a major city. It was formally chartered as Argonne National Laboratory in 1946 and began developing nuclear reactors for peaceful purposes.

Armstrong, Neil (1930-2012): An American astronaut who was the first person to walk on the Moon. He commanded two space flights; the first as the command pilot of Gemini 8, and the second as the mission commander of Apollo 11. It was during the Apollo 11 mission to the Moon that he and Buzz Aldrin exited the spacecraft to walk on the surface of the moon.

array: A series of telescopes that work together as a single telescope.

asteroid: Asteroids are believed to be ancient remnants of the earliest years of the formation of our solar system more than four billion years ago. Most asteroids are made of rock, but some are composed of metal, mostly nickel and iron. They range in size from small boulders to objects that are hundreds of miles in diameter. A small portion of the asteroid population may be burned-out comets whose ices have evaporated away and been blown off into space. Almost all asteroids are part of the Main Asteroid Belt, with orbits in the vast region of space between Mars and Jupiter. Some asteroids pass very close to Earth's orbit around the Sun.

astigmatism: A defect in an lens that prevents light rays from focusing at one point resulting in a blurred image.

astronomical unit: An Astronomical Unit is the mean distance between the Earth and the Sun. In 2012, the International Astronomical Union defined the distance to be 149,597,870,700 meters. All distances in astronomy depend on this value because it is key to deriving distances using parallax.

astrophysics: The part of astronomy that deals principally with the cosmology and the physics of the Universe, including luminosity, density, temperature, and the chemical composition of stars, galaxies, and the interstellar medium.

Atacama Desert: The Atacama Desert is located on the South American Pacific coast, west of the Andes mountains. Due to it’s climate (dry air, minimal cloud cover), it is an ideal location for astronomical observatories.

Atacama Large Milimeter/submillimeter Array (ALMA): The Atacama Large Milimeter/submillimeter Array (ALMA) is an array of 66 interconnected radio antennas that work together as a single telescope, using a technique called interferometry, at millimeter and submillimeter wavelengths. The antennas can be moved closer together or farther apart in order to change the resolution. It’s located at the Llano de Chajnantor Observatory in the Atacama Desert in Chile.

atom: The basic unit of any of the 92 natural elements of the periodic table that cannot be further subdivided without losing the properties of the element.

Atomic Energy Project: Another way of referring to the Atomic Energy Commission, the Federal agency (known as the AEC), which was created in 1946 to manage the development, use, and control of atomic (nuclear) energy for military and civilian applications. The AEC was subsequently abolished by the Energy Reorganization Act of 1974 and succeeded by the Energy Research and Development Administration (now part of the U.S. Department of Energy) and the U.S. Nuclear Regulatory Commission.

Auger (Pierre) Cosmic Ray Observatory: The Pierre Auger Cosmic Ray Observatory is dedicated to studying ultra-high energy cosmic rays, the most energetic and rarest of particles in the Universe. When such a particle strikes the Earth's atmosphere, it creates a shower of lower energy secondary particles, and these are observed to reach the ground. In fact, about a hundred of these secondary particles pass through our bodies every second. But as the energy level increases, the number of particles becomes more and more rare. At 1019eV, only about two particles per square mile arrives at the upper atmosphere per year. Above 1020eV, only about two particles per square mile arrive each century. To find and measure these rare events, a high-energy cosmic ray study needs a truly giant detector, like the 35-mile by 35-mile detector in Malargüe, Argentina, where it occupies an area as large as the state of Rhode Island. Even with an array so large, Auger detects cosmic rays and gamma rays so energetic that they occur at the rate of only a few a year.

aurora: Auroras are colorful, shimmering lights that occur around the poles of planets and some moons, such as Earth, Saturn, Jupiter and Io, a moon of Jupiter. In the case of Earth, particles from solar flares penetrate the upper atmosphere around the magnetic poles. These particles react with and excite the oxygen and nitrogen in the atmosphere, causing colorful light displays. The plural of aurora is sometimes spelled aurorae.

azimuth: The distance in degrees along the horizon, westward from the south point of the horizon, to the place where a vertical circle through the star or other object intersects the horizon.

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Bachall, John (1934- 2005): An American astrophysicst who helped develop the Hubble Space Telescope. He spent his career at Princeton University.

Barkla, Charles Glover (1877-1944): Charles Glover Barkla was a 20th-century English scientist who is primarily recognized for his work in the X-ray field, but also for his reputation as an excellent physics professor and a formidable examiner. One of his most significant discoveries was the polarization of X-rays, which indicated that they were more similar to light on the optical spectrum than previously believed. He was a member of the Royal Society and received the Hughes Medal (awarded for original discoveries in the field of physics) in 1917.

baryonic matter: All material made of of protons, neutrons and electrons.

Becklin, Eric: Eric Becklin is an American astrophysicist at the University of California at Los Angeles. He is the Chief Scientist for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Becklin is also recognized for his scientific research, including his discovery with Gerry Neugebauer of a bright infrared source within Orion, known as the Becklin-Neugebauer Object.

Bell Labs: Bell Labs is a research and development firm with facilities in eight countries. It is a subsidiary of French-owned Alcatel-Lucent. In the 1930s, one of Bell Labs engineers, Karl Jansky discovered the first radio signals from an astronomical source marking the beginning of the field of radio astronomy.

BeppoSAX: Launched on April 30, 1996, BeppoSAX was a Italian-Dutch X-ray astronomy satellite named in honor of Italian physicist, Giuseppe "Beppo" Occhialini. SAX stands for Satellite per Astronomia a raggi X (Italian for Satellite for X-ray Astronomy). BeppoSAX helped determine the origin of gamma-ray bursts. It ceased operations on May 2, 2002 and reentered Earth's atmosphere on April 29, 2003.

Bessel, Friedrich (1784-1846): A German astronomer and mathematician who made many advances in the precise measurement of the stars over his lifetime. In 1838, he was the first to record a reliable measurement of the measurement of a star which allowed him to calculate the distance to the star.

beta radiation (β): Beta radiation occurs when an electron is emitted from a nucleus along with an antineutrino, a very small particle which carries away some of the energy of the emission.

Big Bang: The expansion of the Universe from a very small volume filled with energy, electrons, and quarks through a cooling phase including nucleosynthesis and the eventual creation of galaxies.  Today's galaxies still reflect the expansion set in place by the Big Bang.  What happened before the Big Bang, namely the creation of a very massive, hot aggregate of subatomic particles, electrons, and photons, is unknown and is a question at the frontier of physics.  In the beginning, in the quark phase, the excited material began to collide as the Universe continued to expand and cool, forming neutrons and protons (hydrogen).  The collisions of the atomic particles would then form the more complex elements, helium and lithium.  At three minutes old, the temperature of the Universe was 1 billion degrees.  It took 400,000 years for the Universe to cool enough to sustain the creation of elements with larger nuclei.

Bikini Atoll: Bikini is a large coral atoll, a coral reef in a ring-shaped structure, in the Marshall Islands in the Pacific Ocean. between 1946 and 1958, 23 test of nuclear devices were conducted by the United States. This was the site of the first atomic bomb test.

binary neutron star: A pair of neutron stars that orbit around a common center of mass. A neutron star is the imploded core of a massive star produced by a supernova explosion.

binary pulsar: A pulsar with a binary companion, often a white dwarf or neutron star. Physicists use pulsars to test general relativity because of the strong gravitational fields around them.

binary star: A star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary.

black hole: An object whose gravity is so strong, because of a small radius and high-density, that the laws of physics break down: we do not know of what the inside of a black hole is made. Black holes that are remnants of supernovae have masses of a few solar masses. Clusters of massive stars may lead to multiple supernovae which leave behind multiple black holes that subsequently merge into single objects with masses of millions of solar masses. Black holes responsible for quasars have masses of billions of solar masses.

Blackett, Patrick (1897- 1974): An English experimental physicist and winner of the Nobel Prize in Physics in 1948. He is known for his work on cloud chambers, cosmic rays and paleomagnetism.

blazar: A galaxy with a supermassive black hole at its core.

Boltzmann, Ludwig (1844-1906): An Austrian physicist best known for his contributions to statistical thermodynamics, the science of heat and molecular motion. Boltzmann was a student of Stefan's and refined Stefan's law to include grey-body emission as well as black-body emission, thus the law is now known as the Stefan-Boltzmann law.

bolometer: A bolometer operates by measuring the change in temperature caused when light is absorbed within it.

Bohr, Niels (1885-1962): A Danish physicist and winner of the Nobel Prize in Physics in 1922. He is known for his contributions to understanding atomic structure and quantum theory.

Bowyer, Charles Stuart: An astronomer and professor at the University of California. He is credited with starting the field of extreme ultraviolet astronomy.

Braunschweig: A German city located in the state of Lower Saxony.

Brooklyn College: Brooklyn College is one of the senior colleges in the City University of New York system. It was established in 1930.

Buck Rogers: A fictional character who appeared in comic strips, movies and radio and television shows. The character was created by Philip Francis Nowlan and is credited with bringing the concept of space exploration into public media. He was first introduced to the public in 1928.

Bunsen, Robert (1811-1899): A German chemist who worked in the field of spectroscopy. He worked closely with Gustav Kirchhoff and together they invented the spectroscope.

Burst Alert Telescope: The Burst Alert Telescope (BAT) is a highly sensitive instrument with a large field of view that can detect both bright and faint GRBs on the Swift Gamma-ray Burst Explorer. BAT is able to detect GRBs with a variety of intensities, durations, and temporal structures because of its design which includes a two-dimensional coded aperture mask with a large area solid state detector which enable it to detect faint bursts, and a wide field of view which enables it to detect a large number of bright bursts.

Bush, Vannevar (1890-1974): An American engineer, inventor, and early administrator of the Manhattan Project. He was the founder of the company Raytheon, Dean of the MIT School of Engineering, and Chairman of the National Defense Research Council among other jobs throughout his career.

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calibrate: To match the readings of an instrument with those of a standard in order to check the instrument’s accuracy. The process of doing this is calibration.

calorimeter: A device used to measure the heat generated in a chemical reaction or other process.

The California Institute of Technology (Caltech): Caltech, established in 1891 as Throop University, is a private research university located in Pasadena, California.

Canadian Space Agency: The Canadian Space Agency has managed the Canadian space program since 1990. The CSA is an associated member of the European Space Agency and has stratgic partnerships with other space agencies, such as NASA. It is headquartered at the John H. Chapman Space Centre in Longueuil, Quebec.

Canizares, Claude: An American physicist and Vice President of MIT. He has spent his career at MIT since his postdoctoral fellowship and is the Assocaite Director for MIT of the Chandra X-ray Observatory Center.

capacitor: A capacitor is a device that is used to temporarily store an electrical charge.

Cash, Webster: A professor of Astrophysical and Planetary Sciences and Professor of Aerospace Engineering Sciences at the University of Colorado, Boulder.

carbon: The sixth chemical element in the periodic table.

celestial: Positioned in or relating to the sky or outer space.

celestial sphere: an imaginary sphere of which the observer is the center and on which all celestial objects are considered to lie. Source

Cerenkov counter: Cerenkov counters detect the bluish light from gamma rays from astronomical objects when they hit the upper atmosphere of Earth. The gamma rays produce pairs of electrons and positrons (positively and negatively charged particles) that are moving very fast. These particles have velocities above the speed of light in the atmosphere (a speed known as the phase velocity which is equal to the speed of light in a vacuum divided by the index of refraction of air) creating a disturbance, the energy from which is emitted as blue light. The effect is analogous to a sonic boom of a supersonic aircraft or bullet. Also spelled Cherenkov.

Chandra X-Ray Observatory: Named for Subrahmanyan Chandrasekhar, The Chandra X-Ray Observatory was launched by NASA on July 23, 1999 on the space shuttle. It is specially designed to detect X-ray emission from very hot regions of the Universe such as exploded stars, clusters of galaxies, and matter around black holes. Because X-rays are absorbed by Earth's atmosphere, Chandra must orbit above it, up to an altitude of 139,000 km (86,500 mi) in space. Chandra carries four very sensitive mirrors nested inside each other. The energetic X-rays strike the insides of the hollow shells and are focussed onto electronic detectors at the end of the 9.2-m (30-ft.) optical bench. Depending on which detector is used, very detailed images or spectra of the cosmic source can be made and analyzed.

Chandrasekhar, Subrahmanyan (1937-1995): Indian astrophysicist reknowned for creating theoretical models of white dwarf stars, among other achievements. His equations explained the underlying physics behind the creation of white dwarfs, neutron stars and other compact objects.

Cherenkov Light: The blue light emitted when charged particles or gamma-rays interact with air molecules as they travel through the Earth’s atmosphere. It is named after Russian scientist Pavel Alekseyevich Cherenkov (1904-1990). Pavel shared the 1958 Nobel Prize in Physics with colleagues for discovering and interpreting the “Cherenkov Effect,” the observed light that results when high-energy particles pass through matter at a speed greater than the speed of light (186,000 miles per second).

circumgalactic medium: The generally invisible environment around the visible part of a galaxy, consisting of gravitational and electromagnetic fields and flows of matter in and out of the galaxy.

Clark, George: An American astronomer at the Massachusetts Institute for Technology who worked with Bruno Rossi and Riccardo Giacconi in the 1960s to develop the first telescope that focused X-rays using grazing-incidence mirrors.

Clemson University: Clemson University was opened in 1893 as Clemson College, an all-male military school. In 1955 it began admitting women and civilians. It is located in Clemson, South Carolina.

cloud chamber: The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. source

coating:a thin often metallic layer evaporated onto a substrate (the glass of a mirror, for instance) to enhance the efficiency of the mirror in reflecting light at specific wavelengths, or to restrict the wavelength region passed through a filter.

coincidence circuit: In physics, a coincidence circuit is an electronic device with one output and two (or more) inputs. The output is activated only when signals are received within a time window accepted as at the same time and in parallel at both inputs. Coincidence circuits are widely used in particle physics experiments and in other areas of science and technology. Source

Colgate, Stirling: An American physicist at Los Alamos National Laboratory. In the 1950s while at Livermore National Laboratory, Colgate oversaw the testing of the first thermonuclear bomb, called Bravo test.

collapsar: This core collapse occurs while the outer layers of the star explode in an especially energetic supernova dubbed a "hypernova" by astronomers. The term collapsar was coined in 1993 by Stan Woosley, an Astronomy and Astrophysics Professor at the University of California, Santa Cruz.

Columbia University: Columbia University is a private Ivy League research university. It is located in New York City and was established in 1754.

collimated: Light in which the beams are parallel.

comet: Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of kilometers.

compact star: A massive star with a small radius. Also known as a compact object. White dwarfs, neutron stars, and black holes are all compact objects.

Compton, Arthur Holly (1892-1962): An American physicist who won the Nobel Prize for physics in 1927 for work on scattering of high-energy photons by electrons, a process central to the gamma-ray detection techniques of all four instruments onboard the Compton Gamma-Ray Observatory which was named for him.

Compton Gamma-Ray Observatory: Named for Arthur Holly Compton, an astrophysicist from the University of Chicago, CGRO was the second of NASA's Great Observatories, launched in April 1991 on the space shuttle Atlantis. At 17 tons, it was the heaviest astrophysical payload ever flown at the time of its launch. The instruments aboard CGRO covered an unprecedented six decades of the electromagnetic spectrum, from 30 keV to 30 GeV. In order of increasing spectral energy coverage, these instruments were the Burst and Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET). For each of the instruments, an improvement in sensitivity of better than a factor of ten was realized over previous missions. Within months of its launch, BATSE allowed astronomers to monitor the distribution of the gamma-ray bursts across the sky. It was soon clear that they are detected at a rate of about one per day, from all directions.Compton is responsible for the view that gamma-ray bursts are extragalactic. The mission ended in 2000.

constellation: A pattern of stars visible from Earth in the night sky. Most constellations are made up of stars that have no physical relation to one another. Remarkable astronomical phenomena such as supernova remants (Cassiopeia A), sources of extraordinary brightness (Scorpius X-1), and galaxies (Andromeda) are frequently named for the constellation of which they are a part.

convection: The movement of a gas or liquid in a current caused by the warmer matter rising and cooler matter moving in to replace it.

Copernicus: The Copernicus satellite was launched into a nearly circular 7123 km radius orbit, inclined at 35 degrees, on 21 August 1972. The main experiment was an ultraviolet telescope. However, it also contained a cosmic X-ray experiment provided by University College London/MSSL. The main body of Copernicus measured 3 x 2 meters. The solar panels were fixed at an angle of 34 degrees to the observing axis, and were kept within 30 degrees of the Sun. This restriction resulted in certain parts of the sky being visible only at certain parts of the year. The astronomical instruments were co-aligned, with the UV telescope residing in the central cylinder of the satellite and the X-ray experiment in one of the bays surrounding it. While the UV telescope was observing, the X-ray detectors primarily took background measurements. Occasionally, the X-ray detector observed an X-ray source in the field of view of the UV target. It operated until February 1981.

core collapse supernova: Also known as a Type II supernova, a core collapse supernova is the death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradual fading. At peak light output, these types of supernova explosions can outshine a galaxy. The plural forms of supernova are supernovae and supernovas.

Cornell University: Cornell University is an Ivy League school located in Ithaca, New York. It was founded in 1865.

corona: The uppermost level of a star's atmosphere. In the Sun, the corona is characterized by low densities and high temperatures (> 1,000,000 degrees K). The plural of corona is coronae.

Cosmic Background Explorer (COBE): The COBE satellite was developed by NASA's Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early Universe to the limits set by our astrophysical environment. It was launched November 18, 1989 and carried three instruments, a Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared background radiation, a Differential Microwave Radiometer (DMR) to map the cosmic radiation sensitively, and a Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the cosmic microwave background radiation with a precise blackbody.

cosmic background radiation: Electromagnetic radiation near wavelengths of 1mm coming from every direction of the Universe. It is thought to be relic radiation from the Big Bang.

Cosmic Origins Spectrograph (COS): The Cosmic Origins Spectrograph (COS) studies the large-scale structure of the Universe and the formation and evolution of galaxies, stars and planets. It performs spectroscopy, the science of breaking up light into its individual components. Any object that absorbs or emits light can be studied with a spectrograph to determine its temperature, density, chemical composition and velocity.

cosmic rays: Energetic particles that travel through space.

Cosmic Ray Group: The group of researchers led by Bruno Rossi studying cosmic rays, high energy particles of uncertain origins from space.

cosmological: A distance far beyond the boundaries of our Galaxy.

cosmology: The astrophysical study of the history, structure, and dynamics of the Universe.

Coyne, Father George: A Jesuit priest and astronomer who was the director of the Vatican Observatory from 1978 to 2006.

Crab Nebula: The Crab Nebula is a supernova remnant in the Milky Way Galaxy. The supernova explosion was observed by Chinese astronomers in the year 1054.

Crocker, James (Jim): An American engineer who is well-known for his work at Johns Hopkins University leading the design effort for the Advance Camera for Surveys, a scientific instrument installed in the Hubble Space Telescope in February 2002 that improved the performance of the telescope by an order of magnitude.

Cronin, James: An American nuclear physicist. He shared the Nobel Prize in physics in 1980 for showing that the laws of nature operate differently on matter and antimatter. Without this difference, no matter would exist in the Universe at all.

Curie, Marie (1867-1934): A French physicist and chemist of Polish descent and winner of the Nobel Prize in Physics in 1903, with her husband, Pierre Curie, and Antoine Henri Bequerel for their research in radioactivity. She would again win the Nobel Prize in 1911, this time in Chemistry, for her discovery of the elements radium and polonium.

Curie, Pierre (1859-1906): A French physicist who won the 1903 Nobel Prize in Physics for reasearch into radioactivity with his wife, Marie Curie, and Antoine Henri Bequerel.

Curtis, Heber D. (1872-1942): An American astronomer who began his professional career as a professor of Latin and Greek. Astronomy became a hobby and he eventually went back to school for a PhD in Astronomy at the University of Virginia. After receiving his PhD, he was hired at Lick Observatory where he studied spiral nebulae and would eventually publish an article claiming that these nebulae were in fact other spiral galaxies. Another astronomer, Harlow Shapley, disagreed with Curtis's findings arguing that the nebulae were nearby gas clouds. In 1920 Curtis and Shapley debated the issue which has ramifications for the scale of the Universe, an event known as the Great Debate.

Cygnus X-1: Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that results from the collapse of a massive star. In the case of Cygnus X-1, material from a nearby, massive blue companion star is falling into the black hole. This material forms a disk that rotates around the black hole before falling into it or being redirected away from the black hole in the form of powerful jets.

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dark energy: A hypothetical form of energy that affects the expansion of the Universe. Little is known about dark energy.

dark matter: A unknown form of matter that is undetectable by its emitted electromagnetic radiation, but whose presence can be inferred from gravitational effects on visible matter.

Darwin, Charles (1809 - 1882): Darwin was an English naturalist and geologist. He published his theory of evolution by natural selection in his book, On the Origin of Species, in 1859.

data: Pieces of information such as facts, statistics, or measurements that can be collected together for reference or analysis.

David Dunlap Observatory: The telescope at the David Dunlap Observatory in Richmond Hill, Ontario, is the largest general purpose optical telescope in Canada. The primary mirror is more than six feet in diameter (74”) and the telescope itself (without the primary mirror) weighs 23 tons.

dead reckoning: A basic navigational method used by low speed, small airplane pilots. It is based on mathematical calculations to plot a course using the elements of a course line, airspeed, course, heading and elapsed time.

deep: Deep refers to images taken with very long exposure times, capable of picking up very faint objects.

degree: A unit of measurement of angles. There are 360 degrees in a full circle.

density: The mass of an object divided by its volume.

deuterium: One of the two stable isotopes of hydrogen.

dewar: A vacuum-insulated container that can maintain the temperature of its contents over an extended period of time. Hot liquids stay hot and cold liquids stay cold much longer than they would in an un-insulated vessel.

Dicke, Robert (1916-1997): An American physicist who contributed to the discovery of thermal background radiation. He spent his career at Princeton University.

diffraction: The bending of light as it passes over the edge of an object.

diode: A diode is a device that allows electrical current to flow in one direction only.

dirrect current (DC): Direct current is the flow of electricity in one direction.

Doppler effect: A phenomenon where sound or light waves are perceived to change frequency when the source of the sound or light moves relative to the observer.

double star: A pair of stars that are closer together than typical stars in the sky. If observed over a long period of time they will often be seen to change relative position, in which case they are called binary stars. William Herschel is attributed with the discovery of the binary nature of some double stars.

dust grain: The solid particles that make up the dust that is distributed through interstellar space. The dust is mixed in with gas, but the total mas of grains is on the order of 1/100th of the total mass of the gas. See interstellar dust.

dynamics: The study of the motion of bodies of various types, responding to various forces as they travel through space.

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efficiency: The ratio of the amount of light reaching a detector in an instrument to the amount of light that would reach a detector if the instrument were perfect. The term is sometimes applied to individual components of instruments as well. Consider a telescope with two mirrors that produces a focused image of a star (the target) or other object in the focal plane of the mirror system. The light continues through an instrument, say, a spectrograph, which has many reflections and a prism, and lands on a detector which produces a signal, say, a count of the number of photons per second from the target. About 4% of the light may be lost at each reflection in the telescope, so that only 96% of the light from the target star is reflected from the first mirror. Likewise, from the second mirror. This simple telescope is said to be 0.96 x 0.96 = 0.92 efficient, or 92% efficient, because only 92% of the light from the star reaches the focal plane. The light next passes into an instrument: with more losses at mirrors in the instrument, and absorption of light in the prism, the light actually reaching the detector may only be 20% of the amount entering the instrument, or 0.2 x 0.92 =0.184 (18.4%) of what originally entered the telescope. There are usually other losses in the detector, say, 30%. The overall system of telescope, instrument and detector is 0.92 x 0.184 x 0.3 = 0.057 (5.7% efficiency).

efficient: The ratio of the number of events (such as a gamma ray, X-ray, or optical photons) that are counted by the electroniocs of a detector as opposed to the number of events that strike it. Perfect efficiency is difficult to achieve for a number of reasons. For example, the detection of an optical photon by a CCD detector requires that it enters the layer of the detector where it will be converted into electrons. Some photons may be reflected from the surface of the detector and thus never enter the area where they may be detected. Or, some photons may pass through a detector; in this case, the detector is "transparent" (as in a window) to the photon.

Einstein, Albert (1879-1955): German-American physicist who developed the Special and General Theories of Relativity, which along with Quantum Mechanics, are the foundation of modern physics.

Einstein Observatory: The second of NASA's three High Energy Astrophysical Observatories, HEAO-2, renamed Einstein after launch, was the first fully imaging X-ray telescope put into space. It was launched in November 1978 and returned to Earth in April, 1981.

ejecta: Material that is ejected. Used mostly to describe the content of a massive star that is propelled outward in a supernova explosion. Also used to describe the material that is blown radially outward in a meteor impact on the surface of a planet or moon.

electromagnetic spectrum: The full range of frequencies, from radio waves to gamma rays, that characterizes light.

electromagnetism: The science dealing with the physical relations between electricity and magnetism.

electron: A fundamental, lightweight particle carrying a negative electric charge and found in all atoms. Electrons can be energized or even torn from atoms by light and by collisions, and they are responsible for many electric phenomena in solid matter and in plasmas. See proton.

electron volt (eV): A unit of energy sufficient to excite atoms to emit visible light. A typical visible light photon has an energy of 2 eV.

energy: Ability to perform work; to advance against resistance; for instance lift a body against gravity, or drag it against friction.

Enewetak Atoll: Enewetak (sometimes also spelled Eniwetok) is a large coral atoll, a coral reef in a ring-shaped structure, in the Pacific Ocean. During World War II, the United States captured the atoll from the Japanese in he Battle of Eniwetok in 1944. After the war, the United States used the atoll for testing nuclear bombs. There were 43 nuclear tests at Enewetak between 1948 and 1958.

epoch: In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.

error box: Every object in the sky has a coordinate position analogous to longitude and latitude on the surface of the Earth. Just as every house on Earth has a longitude and latitude, every star in the sky has a right ascension (east-west) and declination (north-south). You can find the coordinates for your house using a GPS. Depending on how a source is discovered, the coordinates of a star may be more or less accurate, so it is important to state the range in right ascension and the range in declination in which there is a 90% chance of finding the source with another telescope. This range of uncertainty defines a box on the plane of the sky in which the source will certainly be found. It is called the error box. The smaller the error box, the more accurate the measurement of observation.

escape velocity: The speed needed for an object to break away from the gravitational pull of a planet or moon.

ether: A hypothetical medium filling all of the otherwise empty space in the Universe which light waves were thought to propagate through. The existence of ether was disproved by the Michelson-Morley experiment.

European Southern Observatory (ESO): The ESO is an intergovernmenal organization for astronomy research with headquarters in Garching, Germany. It’s observatories are located in Northern Chile.

European Space Agency (ESA): The European Space Agency (ESA) is an organization with 20 European member states, which writes and carries out space policies and programs. It is headquartered in Paris, France.

exoplanet: A planet that orbits a star other than our Sun.

expansion velocity: The velocity of motion away from a certain point, as in gas expanding around a supernova or galaxies expanding away from each other in the Universe.

Explorer 11: The first gamma-ray detection satellite flown, weighing in at 82 pounds. It was launched on 27 April 1961 and the instrument aboard was designed to detect gamma rays above 50 MeV. The satellite operated well until early September, when power supply problems became noticeable. Useful data ceased soon thereafter.

external reflection: Reflection at a steep angle.

extragalactic: Any object that exists or originated outside of the Milky Way.

extrasolar: Any object that exists outside of our Solar System.

Extreme Ultraviolet Explorer: The Extreme Ultraviolet Explorer (EUVE), a NASA explorer class satellite mission, was launched on June 7 1992 and it operated till January 31 2001. EUVE is entirely dedicated to observations in the wavelength range from 70 to 760 Å. The first phase of the mission (six months) was dedicated to an all-sky survey using the imaging instruments. The second phase instead is dedicated to pointed observations with mainly the spectroscopic instruments.

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Far Ultraviolet Spectroscopic Explorer: The Far Ultraviolet Spectroscopic Explorer (FUSE) was a NASA supported mission that launched June 24, 1999 and observed the Universe using high resolution far-ultraviolet spectroscopy, a region of the electromagnetic spectrum that is blocked by Earth’s atmosphere. After a highly successful eight year observational period, on-orbit activities concluded in mid-October 2007 with the decommissioning of the satellite. FUSE provided a wealth of data that will be studied for years to come.

fascism: An ideology developed in Italy and associated with the the National Fascist Party, led by Benito Mussolini from 1922 to 1943 and by the Republican Fascist Party from 1945 to 1945. Italian Fascism is based on the idea that it was necessary for Italy to expand its territory in order to assert its superiority and strength.

Fastie, William (1916-2000): William Fastie was an American optical physicist who spent his career at Johns Hopkins University. He was well known for developing a revolutionary spectrograph that was used in rocket-borne telescopes and satellites.

Fermi, Enrico (1901-1954): Enrico Fermi was an Italian-born, American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory and nuclear and particle physics. He was awarded the 1938 Nobel Prize in Physics for his work on induced radioactivity. Fermi is widely regarded as one of the leading scientists of the 20th century, and along with J. Robert Oppenheimer, is frequently referred to as "the father of the atomic bomb.” The Enrico Fermi Institute, the Fermi National Accelerator Laboratory, the Fermi Gamma-ray Space Telescope, a class of particles called fermions, and the synthetic element fermium, are all named in recognition of the physicist.

Fermi Gamma-Ray Telescope: Launched June 11, 2008, the Fermi Gamma-ray Space Telescope (formerly known as GLAST) has an imaging gamma-ray telescope vastly more capable than instruments flown previously, as well as a secondary instrument to augment the study of gamma-ray bursts: the Large Area Telescope (LAT) and the Gamma Ray Burst Monitor (GBM). The telescope was named in honor of Enrico Fermi, like Compton, from the University of Chicago, who won the Nobel Prize for physics in 1938 for his work on the artificial radioactivity produced by neutrons, and for nuclear reactions brought about by slow neutrons. In its first year of observations, Fermi captured more than 1,000 discrete sources of gamma rays, five times the number previously known.

Fermi National Accelerator Laboratory (Fermilab): A US Department of Energy national laboratory located in Batavia, Illinois. It specializes in high-energy particle physics.

Fichtel, Carl: Carl Fitchel is an astrophysicist at the NASA Goddard Space Flight Center and was a co-Investigator for the development of the Energetic Gamma Ray Experiment Telescope (EGRET), an instrument on the Compton Gamma Ray Observatory. Fitchel received the 1995 Bruno Rossi Prize of the High Energy Division of the American Astronomical Society for his contributions to the development of the Compton Gamma Ray Observatory mission, the EGRET instrument, and its discovery of gamma-ray blazars.

fifteenth magnitude: Astronomers denote the apparent ( in italics) brightness of stars with a system, based on logarithms, called magnitudes. A factor of 2.5 in brightness is one magnitude. A factor of 100 in intensity is a range of 5 magnitudes. A factor of 10,000 is 10 magnitudes, a factor or 1,000,000 is 15 magnitudes. The intensity of light and therefore the magnitude depends on the intrinsic luminosity of the star as well as its distance. The magnitude scale is reversed from the way we speak of brightness, in the sense that fainter objects have larger numerical magnitudes and brighter objects have lower magnitudes. The brightest stars have magnitude zero. The faintest stars discernible to the human eye are about 6th magnitude. The brightest galaxies are 9th to 12th magnitude. The faintest galaxies recorded are about 30th magnitude. Astronomers define an absolute (in italics) magnitude which is the intrinsic luminosity of an object and does not depend on distance.

filter: Filters work by blocking a specific part of the color spectrum.

Fishman, Gerald (Jerry): An American high-energy astrophysicist who is a research scientist at Marshall Space Flight Center in Huntsville, Alabama. Fishman was the Principal Investigator for the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory and is currently a co-investigator on the Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-Ray Space Telescope.

fission ratio: The fission ratio is the relative probability that an encounter with a neutron and a heavy atomic nucleus will be absorption of the neutron by the nucleus or the splitting of the heavy nucleus into two smaller nuclei, called fission. The former occurs when the energy of the neutron is low; the fission ratio is said to be high. The latter occurs when the energy of the neutron is relatively higher; the fission ratio is said to be low. When the ratio is large, the neutron will preferentially be captured and a new element with a heavier nucleus will be formed. If the nucleus is uranium-238 (U-238) and the neutron energy is low, the latter outcome produces plutonium 239 (P-239). When the fission ratio is small, the atom will split, releasing atomic energy.

florin: An Italian gold coin; approximately 20,000 modern US dollars.

flux: The measure of the flow of some quantity per unit area per unit time.

focal plane: The plane in a telescope where light rays come into focus.

Franck, James (1882-1964): James Franck was a German physicist. He won the Nobel Prize in Physics in 1925 for his discovery of how electrons impact atoms. He shared the award with Gustav Ludwig Hertz.

Fraunhofer, Josef (Joseph) von (1787-1826): A German physicist who apprenticed under a glassmaker as a young man. He would eventually become the director of the Optical Institute at the Benediktbeuern monastery. He made the finest optical glass in the world at the time and invented precise methods for measuring the dispersion of light and the spectroscope, with which he would discover 574 dark lines in the spectrum of the Sun.

frequency: The number of back-and-forth cycles per second, in a wave or wave-like process. Expressed this way, the frequency is said to be given in units of hertz (hz), named after the scientist who first produced and observed radio waves in the lab. Alternating current in homes in the US goes through 60 cycles each second, hence its frequency is 60 hz; in Europe it is 50 cycles and 50 hz.

Friedman, Herbert (1916-2000): Even though Friedman’s special skill was the development X-ray sensitive Geiger counters, he also developed Geiger counters with high efficiency for gamma rays. Friedman also developed a way for detecting evidence of nuclear explosions through extracting and condensing heavy elements from rainwater. The highly secret NRL project, called Project Rain Barrel, resulted in detecting the first Soviet nuclear explosion in 1949.

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galactic: Referring to properties attributable to galaxies. When the term is capitalized, it refers to properties of our Milky Way Galaxy.

galaxy: A component of our Universe made up of gas and a large number of stars (between one million and a million million stars) held together by gravity. When capitalized, Galaxy refers to our own Milky Way Galaxy.

galaxy cluster: Galaxy clusters are the largest gravitationally bound objects in the Universe. They have three major components: hundreds of galaxies containing stars, gas and dust; vast clouds of hot (30 - 100 million degrees Celsius) gas that is invisible to optical telescopes; and dark matter, an unknown form of matter that is undetectable by its emitted electromagnetic radiation but whose presence can be inferred from its gravitational pull on the galaxies and hot gas. Although the galaxies and hot gas clouds are very massive, scientists have determined that about 10 times more mass is needed to hold the cluster together. It is thought that dark matter provides the additional gravity. Astronomers think that galaxy clusters form as clumps of dark matter and their associated galaxies are pulled together by gravity. These form small groups of galaxies that ultimately merge into large clusters.

Galaxy Evolution Explorer: The Galaxy Evolution Explorer (GALEX) is an orbiting space telescope observing galaxies in ultraviolet light across 10 billion years of cosmic history.

Galilei, Galileo (1564-1642): Galileo Galilei was an Italian astronomer, mathematician, physicist and philosopher. Galileo sparked the birth of modern astronomy with his discoveries of the four largest moons of Jupiter, of craters on the Moon, of the phases of Venus, of sunspots, and of the countless individual stars that make up the Milky Way Galaxy.

Garmire, Gordon: An American astrophysicist who is co-discoverer of high-energy gamma rays and is responsible for developing many of the data-analysis algorithms used today in high-energy astrophysics.

gamma radiation (γ): Electromagnetic waves of the highest frequencies known, originally discovered as an emission of radioactive substances.

gamma-ray burst (GRB): A burst of gamma rays from space lasting from a fraction of a second to many minutes. The scientific consensus is that some may arise in supernovae explosions in distant galaxies. The detailed physical processes are not understood.

Gamma-Ray Imaging Spectrometer (GRIS): A balloon-borne instrument for high-resolution gamma-ray spectroscopy.  GRIS uses germanium detectors to measure gamma-ray spectral lines, including lines from Supernova 1987A and the Galactic Center.

Gehrels, Neil: An experimental physicist working in gamma-ray astronomy at NASA. His interests include gamma-ray bursts and supernovae. He is Principal Investigator for the Swift gamma-ray burst MIDEX mission.

Geiger counter: Geiger counters measure high-energy particles or radiation. They were used to measure latent radioactivity, such as the radioactivty that remains behind after the explosion of an atomic bomb. They were also flown on early rockets to measure celestial X-rays. An electric signal that corresponds to the light collected by the telescope is produced and measured. The Geiger counter usually contains a metal tube with a thin metal wire along its middle, the space in between sealed off and filled with a suitable gas, and with the wire at about +1000 volts relative to the tube. An ion or electron penetrating the tube (or an electron knocked out of the wall by X-rays or gamma rays) tears electrons off atoms in the gas. Because of the high positive voltage of the central wire, these electrons are then attracted to it. In doing so they gain energy, collide with atoms and release more electrons, until the process snowballs into an "avalanche" which produces an easily detectable pulse of current. With a suitable filling gas, the flow of electricity stops by itself, or else the electrical circuitry can help stop it. The instrument was called a "counter" because every particle passing it produced an identical pulse, allowing particles to be counted but with no information about their energy (except that they must have sufficient energy to penetrate the walls of the counter).

Gemini Program: The Gemini program consisted of a total of 19 launches, 2 initial uncrewed test missions, 7 target vehicles, and 10 crewed missions, each of which carried two astronauts to Earth orbit. Designed as a bridge between the Mercury and Apollo programs, the Gemini program primarily tested equipment and mission procedures and trained astronauts and ground crews for future Apollo missions. The general objectives of the program included: long duration flights; testing the ability to maneuver a spacecraft and to achieve rendezvous and docking of two vehicles in Earth orbit; training of both flight and ground crews; conducting experiments in space; extravehicular operations (standup sessions and spacewalks); active control of reentry to achieve a precise landing; and onboard orbital navigation. The Gemini missions lasted for periods ranging from 5 hours to 14 days.

General Theory of Relativity: The geometric theory of gravitation developed by Albert Einstein, incorporating and extending the Theory of Special Relativity to accelerated frames of reference, and introducing the principle that gravitational and inertial forces are equivalent. The theory has consequences for the bending of light by massive objects, the nature of black holes, and the fabric of space and time.

geophysics: The physics of the Earth.

Georgium Sidus: Latin for “George’s Star”, it was the name that Sir William Herschel gave to the planet he discovered. Originally named after King Gorge III, the planet is now known as Uranus.

Germanium: Germanium is a chemical element with symbol Ge and atomic number 32. Because of its physical characteristics, it is well suited for use in optics.

GeV: A GeV is equal to one billion (109) electron volts.

Giacconi, Riccardo: Italian-born, American physicist and recipient of the 2002 Nobel Prize in Physics for his discovery of cosmic X-ray sources. Giacconi designed and constructed the first X-ray telescopes, which produced sharp images of the X-ray Universe. His team detected for the first time a source of X-rays outside our solar system, and he was the first to prove that the Universe contains background X-ray radiation. He also detected sources of X-rays that most astronomers now consider to be black holes.

globular star clusters: Dense bunches of hundreds of thousands of stars.

Goddard, Robert Hutchings (1882-1945): An American physicist who pioneered the modern liquid-fueled rocket. In 1920, Goddard provided a report to the Smithsonian Institution detailing his ideas for rocket propulsion and proposing that a rocket using such methods could reach the Moon. He successfully tested his first liquid-fueled rocket in 1926 and launched a rocket with a scientific experiment, a barometer and a camera, in 1929. NASA's Goddard Space Flight Center is named for him.

Goddard Space Flight Center (GSFC): NASA’s Goddard Space Flight Center was founded in 1959 as NASA’s first space flight complex. The center is a major U.S. laboratory for developing and operating unmanned scientific spacecraft. Goddard manages many of NASA's Earth observation, astronomy and space physics missions. GSFC is located in Greenbelt, Maryland.

gondola: An enclosure that holds an instrument being carried by a balloon.

Goudsmit, Samuel (1902-1978): A Dutch-American physicist who was well known for conceiving the idea of quantum spin along with George Uhlenbeck in 1925.

grating: Used with optical radiation, it is a dispersing element that spreads white light into the colors of the rainbow and analogously for other wavebands. Gratings consist of closely spaced rulings separated by transparent gaps, the thickness of both depending the wavelength of light for which dispersion is desired.

gravitational waves: Ripples in space-time caused by the motion of objects in the Universe. The most notable likely sources are orbiting neutron stars, merging black holes, and collapsing stars. Gravitational waves are also thought to emanate from the Big Bang. As of 2012, no gravitational waves have been observed.

gravity: A mutual physical force attracting two bodies.

grazing-incidence: X-ray telescopes use paraboloidal mirrors, with very steep sides. If mirrors were used to try to reflect X-rays in the normal way used in the optical, the X-rays would be absorbed instantly. The X-rays have their paths diverted only slightly, by grazing incidence on the steep side of the mirror and are focused to a point. Such mirrors are often nested one inside the other, to gain collecting area.

grazing-incidence mirror: The type of mirror used in a grazing-incidence telescope, it allows incoming light to be reflected off the mirror surface at very shallow angles. There are several designs of grazing-incidence mirrors, including flat mirrors or combinations of parabolic and hyperbolic surfaces. To increase the collecting area a number of mirror elements are often nested inside one another.

Great Observatories Program: A series of four space-borne NASA observatories designed to conduct astronomical studies over four different wavelengths (visible, gamma rays, X-rays, and infrared). An important aspect of the Great Observatories Program was to overlap the operations phases of the missions to enable astronomers to make contemporaneous observations of an object at different spectral wavelengths. The four observatories are Hubble, Compton, Chandra, and Spitzer. Hubble, Compton, and Chandra operated simultaneously for one year; Spitzer was not launched until 2003, three years after Compton ceased to operate in 2000.

guide stars: Stars that are used as reference points so that a telescope can accurately track an object that moves due to the rotation of the Earth.

Gunn, James: James Gunn is an Astronomy professor at Princeton University. Some of his important contributions to the field have been in the areas of galaxy formation and dark matter.

Gursky, Herbert (1930-2006): An American high-energy astrophysicist who was the Superintendent of the Naval Research Laboratory's Space Science Division. During his career he studied cosmic X-ray sources from sounding rockets, was the Principal Investigator of the 1st High Energy Astrophysics Observatory (HEAO -1), and collaborated on many other space-based experiments.

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Hadley, John (1682-1744): English mathematician and inventor who built a reflecting telescope that was larger and produced better images that Newton's. He also invented an improved instrument for measuring angles between stars, known as Hadley's quadrant.

Hale, George Ellery (1868-1938): An American astronomer interested in the evolution of the Sun and stars. In the seven years after graduating from the Massachusetts Institute of Technology in 1890, he revolutionized solar observations with the invention of the spectroheliograph: an instrument that made it possible to photograph the Sun's prominences in full daylight. Hale was a faculty member at the University of Chicago before becoming a trustee of the California Institute of Technology. He would found four of the world's largest and significant telescopes: Yerkes Observatory, Mount Wilson Observatory, Palomar Observatory, and the Hale Solar Observatory.

Halley, Edmund (1656-1742): An English astronomer who is best known for his study of comets.

hard X-ray: High energy X-rays, often from about 10 keV to nearly 1000 keV. The dividing line between hard and soft X-rays is not well defined and can depend on the context.

Harper, Doyal: Doyal (Al) Harper is a Professor of Astronomy and Astrophysics at The University of Chicago. He helped pioneer astronomical research on airborne telescopes, and at the South Pole.

Harrison, Fiona: American astrophysicist at Caltech who is the Principal investigator for the NuSTAR Explorer Mission. She uses NuSTAR, as well as X-ray and optical telescopes, to study black holes, neutron stars, and supernova remnants.

Harvard-Smithsonian Center for Astrophysics: The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe.

Harvard University: Harvard University is a private research university located in Cambridge, Massachusetts. It was established in 1636 and is the oldest university in the United States. The undergraduate program at Harvard University is called Harvard College.

Harwit, Martin: Martin Harwit is a Czech-American astronomer and Professor Emeritus of Astronomy at Cornell University. His research focused on infrared astronomy. He was a pioneer in the field of space-based infrared detectors. He was also the Director of the National Air and Space Museum from 1987 - 1995. He was awarded the Bruce Medal in 2007.

Herbig, George (1920-2013): An American astronomer at the University of Hawaii Institute of Astronomy. He and Guillermo Haro both independently discovered Herbig-Haro Objects, which are clouds of interstellar gas and dust that are associated with the birth of a star.

helium: The second chemical element in the periodic table.

Herschel Space Observatory: The Herschel Space Observatory is a telescope of the European Space Agency. It has the largest single mirror ever built for a space telescope and is the only space telescope to cover the far infrared to sub-millimeter range.

Herschel, William (1738-1822): A German-born British astronomer. He built a 48-inch diameter reflecting telescope in the late 1700s that would be the largest telescope in the world for 60 years. Herschel discovered binary stars; cataloged stars and nebulae; mapped the structure or shape of the Milky Way Galaxy by star gauging, that is counting stars in fixed areas across the sky; discovered the planet Uranus; and made the observations that led to his formulation of the first theory of the evolution of the Milky Way. In addition to these notable achievements, he also was the first to discover radiation outside of the optical waveband, infrared radiation.

Hertzsprung, Ejnar (1873- 1967): A Danish chemist and astronomer who is most well-known for work leading to the eventual Hertzsprung-Russel Diagram, a graph that measures a star's absolute magnitude against its temperature.

Herzberg, Gerhard: A German-Canadian physicist and chemist who is best known for his contributions to molecular spectroscopy and the application of this knowledge to planetary atmospheres. He received the Nobel Prize in Chemistry in 1971 “for his contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals.”

high-energy: Objects that release radiation in the X-ray, gamma-ray and extreme ultraviolet wavelengths are considered to be high-energy. Neutrinos and cosmic rays also fall into this category.

High Energy Astronomy Observatory (HEAO): Beginning in 1977, NASA launched a series of very large scientific payloads called High Energy Astronomy Observatories(HEAO). The first of these missions, HEAO-1 surveyed the X-ray sky almost three times over the 0.2 keV - 10 MeV energy band, provided nearly constant monitoring of X-ray sources near the ecliptic poles. More detailed studies of a number of objects were made through pointed observations lasting typically 3-6 hours.

High-Energy Transient Explorer (HETE-2): HETE-2 was an international collaboration between the U.S., Japan, France, and Italy to detect gamma-ray bursts, determine their location, and relay that information within milliseconds to other astronomers. These astronomers in turn focused their various telescopes on the burst to capture, record, and photograph the afterglow. The unique power of HETE-2 was that it not only detected a large sample of these bursts, but it also relayed the accurate location of each burst in real time to ground-based optical and radio observatories. In 2003, HETE-2 provided solid evidence linking long GRBs to the collapse of massive stars, which signal the births of black holes. The mission ended in 2007.

Houck, James: james Houck is an American astronomer and a Professor of Astronomy at Cornell University. He is currently the principal Investigator for the Infrared Spectrograph on the Spitzer Space Telescope. Houck was also a member of the science team for the Infrared Astronomical Satellite (IRAS).

Hoyle, Fred (1915-2001): Fred Hoyle was an English astronomer at the Institute for Astronomy at Cambridge University. He is best known for his contributions to the theory of stellar nucleosynthesis and for coining the term Big Bang to describe the prevailing theory of the creation of the Universe, a theory that he rejected in favor of the steady-state theory which presents the Universe as eternal, without a beginning or an end. Hoyle was the recipient of many professional awards, including the Bruce Medal (in 1970).

Hubble, Edwin P. (1889-1953): American astronomer whose observations proved that galaxies are "island universes," not nebulae inside our own Galaxy, among other achievements. He also found that all far away objects (such as other galaxies) in the Universe are moving away from us, and that this motion, called their recession velocity, is greater the further they are from us. These observations led to his formulation of Hubble’s Law in 1929. The Hubble Space Telescope is named in his honor.

Hubble expansion: Named after Edwin Hubble who discovered that the Universe is expanding, Hubble expansion describes how galaxies move away from each other at a recessional velocity (v) equal to it’s distance away from Earth (d) multiplied by a constant of proportionality called Hubble’s constant (Ho), which is believed to be around 70.0 (km/sec)/Megaparsec.

Hubble Space Telescope: Named for Edwin Hubble, the Hubble Space Telescope is a telescope that orbits Earth. Its position above the atmosphere affords it a view of the Universe that far surpasses in many respects that of ground-based telescopes. Hubble is a type of telescope known as a Cassegrain reflector. Light hits the telescope's main mirror, or primary mirror. It bounces off the primary mirror and encounters a secondary mirror. The secondary mirror focuses the light through a hole in the center of the primary mirror that leads to the telescope's science instruments. A unqiue aspect of Hubble is that it was designed to be serviced by astronauts, so that instruments could be changed from time to time. The instrument complement has consistently provided ultraviolet spectroscopy, and optical and near-infrared imaging.

Huggins, William (1824-1910): An English astronomer who used spectroscopic methods to make observations of stars.

Hulburt, Edward O. (1890-1982): Edward O. Hulburt was an American scientist. He spent his career at the Naval Research Laboratory. He was one of the scientists who participated in the discovery of the ionosphere of Earth.

hydrogen: The lightest and most abundant element in the Universe. It is composed of a single electron and a single proton.

hydrogen bomb: A weapon that uses both hydrogen fusion and uranium fission to create a massive explosion.

hypernova: The death explosion of a star that is at least 30 times more massive than our Sun. These explosions produce some 100 times more energy than supernova explosions. The plural forms of hypernova are hypernovae and hypernovas.

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Ikeya-Seki: Comet Ikeya-Seki, named for the two astronomers who discovered it, was first observed with a telescope in September of 1965. By mid-October the comet was clearly visible in the daytime sky and was one of the brightest comets to be seen in the last thousand years. By early 1966 it had faded from view.

Indiana University: Indiana University is a public research university with eight campuses throughout the state of Indiana. The core campuses are in Bloomington and Indianapolis. It was founded in 1820.

infrared: Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum. The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic.

Infrared Astronomical Satellite (IRAS): IRAS was a joint project of the United States, the United Kingdom, and the Netherlands that operated in space for 11 months in 1983. The satellite surveyed 96% of the sky in infrared. Over 500,000 infrared sources were observed at 12, 25, 60, and 100 microns. The number of discoveries associated with formation of stars and planets are attributable to the satellite. The discoveries include disks in other planet systems, a number of starburst galaxies, and a large number of protostars.

infrared astronomy: The detection and study of the infrared radiation (heat energy) emitted from objects in the Universe.

Institute of Astronomy, Cambridge: A department at the University of Cambridge that teaches and does research in the fields of theoretical and observational astronomy. It was founded in 1972.

interferometer: A device that uses interference of light to obtain higher spectral resolution than can be efficiently obtained with normal spectrographs. Interferometers are also used to obtain higher spatial resolution than can be obtained with normal telescopes. In the case of acquiring improved spatial resolution, a collection of small telescopes spread out over a wide area is used.

interferometry: Interferometry is the use of a specially made device, the interferometer, to achieve high spatial or spectral resolution.

internal reflection: Internal reflection refers to an angle of incidence for x-rays at which all the x-rays are reflected. X-rays hitting at larger angles would be totally absorbed by mirrors.

International Ultraviolet Explorer: The International Ultraviolet Explorer (IUE) was a highly successful astronomical observatory satellite that was in use between 1978 and 1996. It It was an international collaboration between three groups: NASA, the European Space Agency (ESA), and the United Kingdom's Science and Engineering Research Council (SERC; now Particle Physics and Astronomy Research Council, or PPARC).

International X-ray Observatory: The International X-ray Observatory (IXO) is a new X-ray telescope with joint participation from NASA, the European Space Agency (ESA), and Japan's Aerospace Exploration Agency (JAXA) to be launched in the future. IXO will address a variety of science questions in a wide range of topics from stars to quasars, from galaxies and black holes to dark energy and planet formation.

intergalactic medium: The matter that exists in the space between galaxies.

interstellar dust: Solid particles distributed through space. They are generally thought to range in size from 0.1 microns to greater than 1 micron and to be made of minerals, somewhat like ground-up asteroids. The dust contains heavy chemical elements that originated in stars. Many details about the dust grains are not known.

interstellar gas: The atomic and molecular gas (primarily hydrogen and helium) that fills the space between stars.

interstellar medium: The matter that exists in the space between stars within galaxies.

invisible radiation: Refers to electromagnetic radiation to which the human eye is not sensitive. That is, radiation that can be sensed with various kinds of detectors, but which is not part of the normal rainbow colors that the human eye can see. This generally means outside of the wavelength regions of 3800 Angstroms (blue) to 7000 Angstroms (red).

ion: An atom or molecule that has lost or gained one or more electrons and has become electrically charged as a result.

ionization: The process by which ions are produced, typically occurring by collisions with atoms or electrons, or by interaction with electromagnetic radiation.

ionization chamber: An instrument used to measure the number of ions within a gas. The chamber consists of a gas filled enclosure between two conducting electrodes. When gas between the electrodes is ionized by any means, such as by alpha particles, X-rays, or other radioactive emission, the ions and dissociated electrons move to the electrodes of the opposite polarity, thus creating an ionization current that can be measured.

ionosphere: The uppermost part of the atmosphere, which is ionized by solar radiation.

Istanbul University: Istanbul University is a Turkish University located in Istanbul.

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James Franck Institute: The James Franck Institute was established after World War II. It is an American Institution devoted to interdisciplinary research in the fields of physics, chemistry and material science. It is located on the campus of the University of Chicago.

James Webb Space Telescope (JWST): The James Webb Space Telescope (JWST) is a 6-meter, infrared-optimized space telescope. The telescope is so large that it will not fit into an existing launch vehicle. The mirror is segmented so it can be launched in a compact configuration and deploued in space. The project is working to a 2018 launch date.

Jansky, Karl (1905-1950): Karl Jansky was an electrical engineer who in 1931 first discovered radio signals coming from the Milky Way Galaxy when he was working for Bell Labs to identify sources of radio waves that might interfere with transatlantic radio communication.

Jastrow, Robert (1925- 2008): Robert Jastrow was an American astronomer, physicist and cosmologist. He was the founder of the Goddard Institute for Space Studies and and was a well-known author of astronomy related articles in popular magazines and host of space science television programs.

Jet Propulsion Laboratory, NASA (JPL): The JPL is a research and development facility that was established in the 1930s. It is managed by the California Institute of Technology for NASA. It is located in Pasadena, California.

Johns Hopkins University: Johns Hopkins University is a private research university. It was founded in 1876 and is located in Baltimore, Maryland.

Johnson, Harold (1921-1980): Harold Johnson was an astrophysicist at the Lunar and Planetary Laboratory at the University of Arizona and then at the National University of Mexico. He is best known for building the first near-infrared photometers. In an essay on the history of modern infrared astronomy, Frank Low referred to Johnson as the first modern infrared astronomer.

Johnson Space Center: The Johnson Space Center is a NASA facility located in Houston, Texas where astronauts are trained and where flight control for human spaceflight takes place.

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Kennedy, John F. (1917-1963): John F. Kennedy was the 35th President of the United States. One of the things he is remembered for is making the goal of landing a man on the Moon a priority for the country. He was assassinated in 1963, six years before the goal was reached.

Kennedy Space Center: NASA’s John F. Kennedy Space Center was founded in 1962 and is the site where every manned NASA space mission as well as many unmanned scientific missions have launched. It is located on Merritt Island, Florida.

Kepler: The Kepler Mission is a NASA Discovery Program for detecting potentially life-supporting planets around other stars. All of the extrasolar planets detected so far by other projects are giant planets, mostly the size of Jupiter and bigger. Kepler is poised to find planets 30 to 600 times less massive than Jupiter. The Kepler satellite has a 0.95-meter diameter telescope that is a photometer having a field of view a bit over 10 degrees square (and area of sky the size of about two open hands). It is designed to continuously and simultaneously monitors brightnesses of 100,000 stars brighter than 14th magnitude in the constellations Cygnus and Lyrae. Kepler was launched in March 2009.

keV: A keV (or kiloelectron volt) is equal to 1000 electron volts.

Kirchhoff, Gustav (1824-1887): A German physicist who did work in the field of spectroscopy and the emission of black-body radiation. He worked closely with Robert Bunsen and together they invented the spectroscope.

Kitt Peak National Observatory: An observatory located on the Tohono O’odham Reservation in southern Arizona. It is the worlds largest collection of optical telescopes.

Klebesadel, Ray: A physicist and electrical engineer at Los Alamos National Laboratory. Klebesadel worked on the Vela satellite program, and with colleagues Toy Olsen and Ian Strong discovered the first observed gamma-ray burst among the data from the Vela 4 satellites.

Kleinmann, Doug: Doug Kleinmann is an American astronomer who, with Frank Low, discovered the Kleinmann-Low Nebula, a prototypical very early star formation region.

Kleinmann, Susan: Susan Kleinmann is an American infrared astronomer. Kleinmann was an early participant in the nascent field of infrared astronomy and worked on pulsating stars with the Whole Earth Telescope and white dwarfs with the Sloan Digital Sky Survey. She was also a Scientific Editor of the Astrophysical Journal in 1998.

Königsberg Observatory: An astronomical observatory that was located in Königsberg, Prussia attached to the Albertina University of Königsberg. It was destroyed in 1944 during World War II.

Konus: A Russian experiment flown on the United States' NASA Wind satellite in 1994. Konus was the first Russian experiment to fly on an American satellite and continues to monitor gamma-ray bursts, soft gamma repeaters, and solar flares. 

Kraushaar, William: An American physicist who was a pioneer in the field of high-energy astronomy. He directed the development of Explorer 11.

Kron, Richard: Richard Kron is a professor of Astronomy and Astrophysics at the University of Chicago. His main area of research is extragalactic astronomy.

Kuiper Airborne Observatory: Dedicated on May 21, 1975, the Kuiper Airborne Observatory, often called the Kuiper or the KAO, was based at NASA Ames Research Center, located in California's Silicon Valley. Converted from a Lockheed C-141 military cargo plane, the KAO carried a 36-inch reflecting telescope capable of conducting infrared astronomy, and flew at altitudes of 41,000 to 45,000 feet, above 99 percent of the Earth's infrared-absorbing water vapor. It was retired in 1995.

Kuiper, Gerard (1905-1973): Gerard Kuiper was an astronomer at the University of Chicago’s Yerkes Observatory from 1937 to 1960, at which time he established the Lunar and Planetary Laboratory of the University of Arizona. He is widely regarded as the father of planetary science and is known for his discoveries including discovering a moon orbiting Neptune (Nereid), a moon orbiting Uranus (Miranda), and his theories including the existence of the Kuiper Belt, a region of minor planets outside of the orbit of Neptune, and that Saturn’s rings are composed of ice. He was also a pioneer of infrared airborne astronomy.

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Lamb, Donald Q: An American astrophysicist at the University of Chicago.  In 1995, 75 years to the week after the Curtis-Shapley "Great Debate" and in the same auditorium, he debated "The Distance Scale to Gamma-Ray Bursts" with Bodhan Paczynski. He was also the mission scientist for the HETE-2 satellite and was able to use the data to identify colliding compact stars as the cause of short gamma-ray bursts.  

Large Binocular Telescope: The Large Binocular Telescope Interferometer, or LBTI, is a ground-based instrument connecting two 8-meter class telescopes on Mount Graham in Arizona to form the largest single-mount telescope in the world. The interferometer is designed to detect and study stars and planets outside our solar system.

Large Hadron Collider: The Large Hadron Collider (LHC) is the world's largest particle accelerator. It is part of the accelerator complex at the European Organization for Nuclear Reasearch (CERN) and is located in tunnel 17 miles in circumference beneath the border of France and Switzerland near Geneva, Switzerland.

laser: A type of single color (monochromatic) light where all wavelengths are lined up (coherent) and traveling in the same direction, exactly parallel to each other (collimated). Because the laser light is monochromatic, coherent, and collimated, all of its energy is focused to produce a small point of intense power.

Lawrence, Ernest O. (E. O.) (1901-1958): Ernest O. Lawrence was an American physicist known for his invention of the cyclotron atom-smasher in 1929, and for his later work in uranium-isotope separation for the Manhattan Project, the World War II project that developed the first nuclear weapons. He had a long career at the University of California, Berkeley, where he was a Professor of Physics from 1928 until his death. At the age of 37, Lawrence was awarded the Nobel Prize in Physics in 1939 for his work in inventing the cyclotron and developing its applications. Chemical element number 103 is named "lawrencium" in his honor.

Lawrence Livermore National Laboratory (LLNL): LLNL is a scientific research laboratory founded by the University of California in 1952 located in Livermore, California. It was established at the height of the Cold War to meet urgent national security needs by advancing nuclear weapons science and technology.

Learjet: An American company that manufactured business jets between its founding in 1960 and 1990, when it became incorporated into Bombardier. NASA used a Learjet 25, a twin-engine aircraft capable of flying at high altitude to establish its Airborne Astronomy Program.

Leavitt, Henrietta (1868-1921): An American astronomer at the Harvard College Observatory. After graduating from Radcliffe College, she worked at the Observatory counting stars on photographic plates for $.30 per hour. She cataloged thousands of variable stars and in 1912 was able to determine that Cepheid variables, which are more luminous, have longer periods than other variable stars. Her work with these stars led to the true distance scale of the Universe, which is much larger than was imagined before her work.

lepton: A fundamental particle of matter. An electron is an example of a charged lepton, and a neutrino is an example of a neutral lepton.

Lewin, Walter: A Dutch Astrophysicist who was the first to discover a slowly rotating neutron star using all-sky balloon surveys. He has spent much of his career at MIT.

Lick Observatory: An astronomical observatory owned by the University of California. It is located on Mount Hamilton east of San Jose. Lick Observatory is home to nine research-grade telescopes.

light year: The distance light can travel in one year, which is 9,460,730,472,580,800 meters, or 9.5 x 1015 meters.

Lilienthal Observatory: An astronomical observatory in Lilienthal, Lower Saxony, Germany. It was built in the 1780s, fell into disrepair in the early 1800s and was demolished in 1850.

Linsley, John (1925-2002): An American physicist who was a pioneer in the field of ultra-high-energy cosmic rays.

lithium: The third chemical element in the periodic table.

Los Alamos National Laboratory (LANL): Established in 1943, LANL is a United States Department of Energy (DOE) national laboratory located in Los Alamos, New Mexico. Once the site of a boys' ranch school, LANL became home to the Manhattan Project, which was a secret effort to develop a nuclear weapon. The laboratory is one of the largest science and technology institutions in the world that conducts multidisciplinary research for fields such as national security, outer space, renewable energy, medicine, nanotechnology, and supercomputing. Los Alamos is one of two laboratories in the United States where classified work towards the design of nuclear weapons is undertaken. The other is Lawrence Livermore National Laboratory.

Los Alamos Ranch School: Founded in 1917, the Los Alamos Ranch School was a college preparatory school in Los Alamos, New Mexico, for boys aged 12-18. In addition to having a typical college preparatory curriculum, the school focused on the outdoors and community service projects. The school was closed on December 8, 1941, the day after the Japanese attack on Pearl Harbor, so that the U.S. Government could use the site as the home for the Manhattan Project.

Low, Frank (1933-2009): Frank Low was an American solid-state physicist and astronomer. He began his career at Texas Instruments, where he developed a low-temperature thermometer that could be used as a sensitive detector of infrared light. Low went on to pioneer infrared astronomy and infrared technology at the National Radio Astronomy Observatory, Rice University, and the University of Arizona. He was a member of the project teams for the Infrared Astronomy Satellite (IRAS) and the Spitzer Space Telescope.

Lunar and Planetary Institute: The Lunar and Planetary Institute is a research institute that provides support services to NASA and the planetary science community, and conducts planetary science research under the leadership of staff scientists, visiting researchers, and postdoctoral fellows.

Lunar and Planetary Laboratory: The Lunar and Planetary Laboratory is a research center for the study of planetary and solar system science. The lab was founded by Gerard Kuiper in 1960.

Lyman alpha line: One of a series of emission and absorption lines associated with the hydrogen atom, specifically the movement of electrons between the lowest energy level (referred to as n=1) and the second lowest energy level (n=2).

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magnetic field: Magnetic fields are areas where an object exhibits a magnetic influence.

magnitude: A scale used to measure the brightness of a star. The scale ranges from 0 (brightest) to 30 (dimmest). Every 5 magnitudes represents a factor of 100 in brightness.

main sequence star: A star in the phase of its life where the interior heat and radiation of the star is provided by nuclear reactions.

Marshall Space Flight Center (MSFC): Marshall Space Flight Center was formed by NASA in 1960 and is s NASA’s designated developer and integrator of launch systems. MSFC also manages the paylod delivery for and experiments aboard the International Space Stations. MSFC contributes to space science by, among many other initiatives, assisting in the design and building of telescopes, as well as testing large telescope mirrors in the world's only facility for testing mirrors of a certain size in a space-simulated environment. MSFC is located in Huntsville, Alabama.

Mather, John C.: Dr. John C. Mather is a Senior Astrophysicist in the Observational Cosmology Laboratory at NASA's Goddard Space Flight Center. His research centers on infrared astronomy and cosmology. He is also the Senior Project Scientist for the James Webb Space Telescope. He is best known for his research on the cosmic microwave background for which he was awarded the Nobel Prize in Physics in 2006 along with George Smoot.

Massachusetts Institute of Technology (MIT or M.I.T.): Massachusetts Institute of Technology is a private research university. It was founded in 1861 and is located in Cambridge, Massachusetts.

massive star: A star that is more than twice as massive than our Sun.

McCammon, Dan: Dan McCammon is a Professor of Physics at the University of Wisconsin-Madison. He is an expert on on developing X-ray detectors to study very hot parts of interstellar and intergalactic space.

McDonald Observatory: The McDonald Observatory is a facility of the University of Texas at Austin. It was established in 1933 and houses one of the worlds largest optical telescopes, the 9.2 Meter Hobby-Eberly Telescope. It also houses three other reflecting telescopes. The observatory is located in Jeff Davis County, Texas.

megaparsec: 1 million parsecs. A parsec is the unit of distance outside the solar system. 1 parsec is equal to 3.26 light years or 30,800,000,000,000 km.

metallicity: In astronomy, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. The metallicity of an astronomical object may provide an indication of its age. According to the Big Bang theory, when the Universe first formed it consisted almost entirely of hydrogen and helium, trace amounts of lithium and beryllium, and no heavier elements. Therefore, older stars have lower metallicities than younger stars such as our Sun.

metallurgy: Metallurgy is the study and science of metallic elements and their mixes, called alloys.

MeV: A megaelectronvolt; equal to 1 million electron volts (10^6).

Michelson-Morley experiment: An experiment first published in 1887 by Albert Michelson and Edward Morley. The two scientists used a Michelson interferometer, which used mirrors, a glass plate, a light source and a detector to measure the speed of the Earth through the ether. The result was repeatedly zero, which disproved the existence of ether.

microscopy: The technical field of using microscopes to view samples or objects that cannot be seen with the unaided eye.

Mirror Lab: Housed in the University of Arizona’s Steward Observatory, the Mirror Lab is where scientists make giant, lightweight mirrors for optical and infrared telescopes. The mirrors have a honeycomb structure that allows the mirrors to be larger and lighter than solid mirrors.

model: A detailed mathematical description of a hypothetical phenomenon.

molecular hydrogen: Molecular hydrogen, also known as H2, is a molecule made of two hydrogen atoms that share their electrons.

molecular oxygen: Molecular oxygen, also known as O2, is a molecule with two oxygen atoms. Molecular oxygen makes up about 20% of the atmosphere of Earth and absorbs ultraviolet radiation coming from astronomical objects, requiring astronomers to use instruments above the atmosphere to observe in certain wavelengths.

molecule: A group of two or more atoms held together by a chemical bond.

Moos, Warren: Warren Moos is an American astrophysicist. He has spent his career at Johns Hopkins University working in the field of ultraviolet astronomy.

Morton, Donald: Don Morton is a Canadian Astrophysicist. He spent his career at Princeton University, the Anglo-Australian Observatory and the Institute of Astrophysics, National Research Council in Canada where he is Researcher Emeritus.

Mount Wilson Observatory: An astronomical observatory in the San Gabriel Mountains in Southern California near Pasadena. It is home to the historic Hooker 100-inch and Hale 60-inch telescopes .

Multiple Mirror Telescope: An astronomical observatory located on Mt. Hopkins, south of Tucson, Arizona. It is a joint venture of the Smithsonian Institution and the University of Arizona.

multiplexing: In astronomy, multiplexing refers to the multiple information elements that are moving along the spectrum simultaneously.

Museum of Science and Industry: A science museum in Chicago, Illinois, that opened in 1933. The museum features interactive, hands-on exhibits. It was originally referred to as the Rosenwald Museum of Science and Industry after Julius Rosenwald, the chairman of Sears, Roebuck and Company, who provided $3 million dollars in 1926 to start the museum.

muon: A subatomic particle which is similar to an electron but with a mass around 200 times greater. It only exists for a fraction of a second before decaying.

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nanometer: One millionth of a millimeter, or 10-9 meters. The peak of the energy spectrum of the Sun is at a wavelength of 600 nanometers.

NASA Astrobiology Institute: NASA established the NASA Astrobiology Institute in 1998 as an innovative way to develop the field of astrobiology and provide a scientific framework for flight missions. Astrobiology is the study of the origins, evolution, distribution, and future of life in the Universe. This interdisciplinary field requires a comprehensive, integrated understanding of biological, planetary, and cosmic phenomena.

National Bureau of Standards: Now known as the National Institute of Standards and Technology (NIST). NIST is a United States agency that focuses on Metrology, the science of measurement.

National New Technology Telescope: This telescope is the largest in the world that was made to operate in the submillimeter wavelength region. Its name was changed to the James Clerk Maxwell Telescope. It is located at Mauna Kea Observatory in Hawaii.

National Optical Astronomy Observatory (NOAO): The NOAO is an astonomical observatory headquartered in Tucson, Arizona. It’s the U.S. national observatory for ground based nighttime ultraviolet, infrared and optical astronomy.

National Science Foundation (NSF): The NSF is a grant-awarding federal agency that supports all fields of fundamental science and engineering.

nebula: A nebula is a cloud of gas and dust in space. Some nebulas are regions where new stars are being formed, while others are the remains of dead or dying stars. Originally, galaxies were included in the class of objects called nebulae, before theirs distances and stellar makeup were recognized. The word nebula comes from the Latin word for cloud.

Neugebauer, Gerry (1932-2014): Gerry Neugebauer was an American astrophysicist and professor of physics at the California Institute of Technology. At Caltech, he was the chairman of the division of physics, mathematics, and astronomy, as well as the director of the Palomar Observatory. Neugebauer was also the scientific director of the Infrared Astronomical Satellite (IRAS), for which he developed infrared instruments. He was the recipient of both the Herschel Medal (1998) and the Bruce Medal (2010).

neutron: A basic unit of all atoms made up of three fundamental particles called quarks. It has no charge and a mass is almost the same as that of a proton.

neutron star: The imploded core of a massive star produced by some supernova explosions. Neutron stars were first observed in the 1960s as sources of pulsed radio radiation (pulsars).

New Mexico Tech: New Mexico Tech, founded in 1889 as New Mexico School of Mines, is a state science and engineering University located in Socorro, New Mexico.

Newton, Sir Isaac (1643-1727): An English physicist and mathematician, he is best known for his contributions to the understanding of gravity and light (and optics), and for the development of the calculus.

Nixon, Richard M. (1913-1994): Richard Nixon was the 37th President of the United States.

Nobel Laureate: A winner of a Nobel Prize.

Nobel Prize: A set of awards for contributions in Physics, Chemistry, Physiology or Medicine, Literature, and Peace. Prizes are awarded yearly by Scandinavian institutions. The awards were established in 1901 at the behest of Alfred Nobel, a Swedish chemist who invented dynamite.

Northwestern University: Northwestern University is a private university in Evanston, Illinois. It was founded in 1851.

nuclear fission: The process in which the nucleus of an atom splits into smaller parts, often producing free neutrons and photons in the form of gamma-rays, and releasing a very large amount of energy.

nuclear force: The force between two or more nucleons. It is what binds protons and neutrons into atomic nuclei.

nuclear fusion: The process by which two or more atomic nuclei join together to form a single heavier nucleus. This is usually accompanied by the release of large quantities of energy. Fusion is the process that powers active stars and the hydrogen bomb.  The most common use of fusion involves the light nuclei of hydrogen and helium.

nuclear physics: The field of physics which studies the parts of atomic nuclei and their interactions.

nuclear pile: Also known as a nuclear reactor. This is a device that is used to start and control a nuclear reaction.

Nuclear Test Ban Treaty: An international treaty that prohibited the testing of nuclear weapons under water, in the atmosphere, or in space. This limited ban on the testing of nuclear weapons was signed by the United States, the Soviet Union, and the United Kingdom in 1963.  A more comprehensive treaty banned all testing of nuclear devices was signed by 71 nations in 1996.

nucleosynthesis: The process through which lighter nuclei fuse through nuclear fusion to make heavier nuclei. Most elements in the Universe heavier than helium are created when nucleosynthesis occurs in stars.

nucleus: The small concentration of positively charged protons and uncharged neutrons located at the center of atoms or ions. In an atom, the net positive charge of the nucleus is balanced by the net negative charge of the orbiting electrons. Ions have a net positive charge because the number of protons is greater than the number of electrons. The nucleus contains 99.95% of the mass of an atom. The plural of nucleus is nuclei.

NuSTAR Explorer Mission (2012-): An Earth-orbiting satellite with two co-aligned, grazing incidence telescopes, each with a 10-m focal length and specially coated optics. Using newly developed detectors NuSTAR maps the high-energy X-ray sky, including sources such as collapsed stars, black holes, and young supernova remnants.

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O’Dell, C. Robert: C. Robert O’Dell is an American astronomer who has worked at the University of Chicago, NASA, Rice University, and Vanderbilt University. He was the Chief Scientist of NASA’s Hubble Space Telescope Project. He studies the observational astrophysics of gaseous nebulae.

Oberlin College: Oberlin College is a private liberal arts college located in Oberlin, Ohio. It was founded in 1833.

Oberth, Herman (1894-1989): A German physicist and engineer whose early experiments with rockets included a young Wernher von Braun who would go on to become the first director of the NASA Marshall Space Flight Center.

Occhialini, Giuseppe (1907- 1993): An Italian physicist who was known for his work with elementary particles and contribution to the discovery of the pi-meson decay.

occult: In astronomy, one looks a long a line of sight to what are often very tiny sources as measured in angle. The light may be blocked from reaching Earth by objects lying on the line of sight: such stars are said to be occulted. The light of one star could be blocked by another star of similar or greater size, in a distant binary system, or, may be blocked from entering an instrument at the focus of a telescope by a tiny grain of dust.

Olbers, Heinrich Wilhelm (1758-1840): A German physician and astronomer who discovered several asteroids and a periodic comet.

Olson, Roy: A scientist at Los Alamos National Laboratory who discovered the first observed gamma-ray burst among the data from the Vela 4 satellites with his colleagues Ray Klebesadel and Ian Strong.

Oort, Jan (1900-1992): Jan Oort was a Dutch astronomer. He made many discoveries and contributions in the field of radio astronomy, including the suggestion that comets come from the same region of the Solar System, which is now known as the Oort Cloud.

Oppenheimer, J. Robert (1904-1967): J. Robert Oppenheimer was an American theoretical physicist and Professor of Physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first nuclear weapons. Oppenheimer and his students made important contributions to the modern theory of neutron stars and black holes, as well as to quantum mechanics, quantum field theory, and the interactions of cosmic rays. As a teacher and promoter of science, he is remembered as a founding father of the American school of theoretical physics that gained world prominence in the 1930s.

optics: The branch of science that deals with the transmission or reflection of light.

Orbiting Astronomical Observatories (OAO): The Orbiting Astronomical Observatories (OAO) were a series of four satellites launched by NASA between 1966 and 1972. NASA planned three observatories of increasing complexity starting with a broad-band UV survey satellite (OAO-A), a moderate resolution spectroscopic satellite (OAO-B) and a high resolution spectroscopic satellite (OAO-C). Two of the missions were successful and two were failures. The program’s overall success increased awareness in the astronomical community of the benefits of orbiting telescopes for optical astronomy. The Orbiting Astronomical Observatory program set the stage for the development of the Hubble Space Telescope (HST) and other orbiting observatories.

Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS-SPAS): The ORFEUS-SPAS missions were flown in 1993 and 1996 to conduct investigations of celestial sources in the far and extreme ultraviolet spectral range, and to increase understanding of the evolution of stars, the structure of galaxies, and the nature of the interstellar medium. ORFEUS-SPAS was a free-flying platform designed to be deployed and retrieved from the space shuttle.

Orbiting Solar Observatories (OSO): The Orbiting Solar Observatories were a series of satellites launched by NASA between 1962 and 1975. They primarily observed an 11-year sunspot cycle in the ultraviolet and X-ray spectra. OSO 1 was launched in 1962. It carried 8 experiments and was the first satellite to have pointed instruments and onboard tape recorders for data storage. OSO 2 was launched in 1965 and it carried 9 experiments. OSO 3 was launched in 1967 and it carried an X-ray and a gamma ray telescope.

order of magnitude: the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the (base 10) exponent being applied to this amount (therefore, to be an order of magnitude greater is to be 10 times as large).

oscilloscope: An instrument which displays visually on the face of a cathode-ray tube instantaneous voltages of electrical signals. Either the intensity or the displacement of the trace may be controlled by the signal voltage.

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Pacific Proving Grounds: Collectively, a number of sites in the Pacific Ocean that were used as nuclear testing sites between 1946 and 1962, including Bikini Atoll and Enewetak Atoll.

Paczynski, Bohdan (1940-2007): A Polish astrophysicist at Princeton University.  He pioneered gravitational microlensing, a process that allows astronomers to see objects that emit little or no light.  In 1995, 75 years to the week after the Curtis-Shapley "Great Debate" and in the same auditorium, he debated "The Distance Scale to Gamma-Ray Bursts" with Don Lamb of The University of Chicago.  He received many awards for his contribution to astrophysics including the Bruno Rossi prize in 2000 and the Bruce medal in 2002.

Paolini, Frank: An X-ray scientist who worked at American Science and Engineering (AS&E). He worked with Riccardo Giacconi, Herb Gursky and Bruno Rossi on the first rocket flight to successfully detect a cosmic source of X-ray emission. It was launched in 1962.

parabola: Parabola must be defined in relation to a spherical surface. A section of a sphere for which all points on the surface are equidistant from the center of the sphere is a spherical surface. Light from stars (described as parallel light) hitting different parts of a spherical surface does not come to a single-point focus. A parabola is a particular curve which focuses parallel light from all points of the surface to a single point focus, unlike a sphere. The spherical surface does not work well for telescopes because the images are blurred. Having a parabolic surface does work well because it produces images that are sharp.

parabolic: A surface shaped like a parabola. See parabola.

parallax: The apparent motion of a relatively close object compared to a more distant background as the location of the observer changes. Astronomically, it is half the angle which a star appears to move as the Earth moves from one side of the Sun to the other.

Parsons, William, 3rd Earl of Rosse (1800-1867): An Anglo-Irish Astronomer who built the 72-inch telescope called Leviathan in 1845, which was the world’s largest telescope for the next 70 years.

particle accelerator: A device that uses electromagnetic fields to propel charged particles, often to nearly the speed of light.

payload: The scientific instruments aboard a rocket, satellite, or balloon.

Penzias, Arno: A German born, American physicist and astronomer who, along with Robert Wilson, accidentally discovered cosmic microwave background radiation (CMB) while they were working as researchers at AT&T Bell Laboratories. CMB was the "smoking gun" in favor of the Big Bang Theory.

perestroika: A political movement implemented by the government of Mikhail Gorbachev in the Soviet Union in the mid 1980s that sought to reform the Communist Party.

PerkinElmer: An American corporation which operates in more than 150 countries around the world. In the 1950s PerkinElmer built the Stratoscope, which was conceived by Martin Schwartzschild. They also built the optical components for the Hubble Space Telescope (HST) in the late 1970s and early 1980s. A flaw in the mirror required corrective optics to be installed on the first service mission to the telescope in 1994, four years after the launch of the HST.

photoelectric effect: A property that causes some materials to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.

photometer: An instrument for measuring light intensity or optical properties of solutions or surfaces.

photomultiplier: An extremely sensitive light detector. Photomultipliers detect ultraviolet, visible and near-infrared light and multiply the current from incoming light up to 100 million times.

photon: The smallest unit (quantum) of light at a given electromagnetic energy. Photons are particles with zero mass, no electric charge, and a wide range of energies, e.g., gamma-rays, X-rays, ultraviolet, optical, and infrared (in decreasing order of energy).

pipeline: Normally used in astronomy to denote a string of software packages the provides reduction or analysis of digital data, one step at a time.

planetary nebula: The glowing nebula around the contracting white dwarf that forms at the end of the evolution of stars below eight solar masses, the expanding residual of the outer envelope of the original star. These nebulae were originally not distinguished from the ionized gas from around hot stars and from external galaxies. They were distinguished by their green color, which was reminiscent to the color of faint planets that were seen by early telescopes.

plasma: A fourth state of matter (in addition to solid, liquid, and gas). In this state, atoms are positively charged and share space with free negatively charged electrons. Plasma can conduct electricity and interact strongly with electric and magnetic fields. The solar wind is actually hot plasma blowing from the Sun.

pointing: Astronomers have to orient their instruments to collect light from any given object. Poining is a verb that refers to the process of changing the telescope position from one star to another. An observation of a particular star is often referred to as a "pointing".

polarization: Light can be represented as an oscillating vector called the E vector that moves sideways through space and oscillates perpendicular to the direction of light motion. The orientation of the vector to the observer is random (up, down, right, left). However, there are processes that selectively absorp or scatter light so that the vectors representing light from a given source may be oriented in a common direction. The operation of such a mechanism is called polarization (as in sunglasses) and the resulting light is said to be polarized. Light from stars that passes through dust clouds have, typically, 1% of the light polarized, owing to a complicated alignment of charged interstellar dust grains by local magnetic fields. The assymmetrical, aligned grains selectively absorb light with electric vectors oriented in one direction with respect to the magnetic fields in space and the resulting light at Earth is polarized. Astronomical sources with very strong polarization may have as much 10% polarization.

pound: A unit of currency used in Great Britain. 50 is about 7500 modern dollars and 200 is about 30,000 modern dollars.

preferred direction: If particles or photons have the same event rate from every part of the sky, they are said to have no direction. If the photons or particles appear to come from one part of the sky or from several sources within the sky, they are said to have preferred directions.

Princeton University: Princeton University is a private research university located in Princeton, New Jersey. It was founded in 1746.

principal investigator: The lead scientist or engineer on a research project.

prism: A transparent optical element that disperses light into the colors of the rainbow. The amount of the dispersion depends on the index of refraction of the glass.

Project Vanguard: An American program managed by the U.S. Naval Research Laboratory that sought to launch the first artificial satellite into Earth’s orbit using the Vanguard rocket. Due to the surprise launch of Sputnick 1 by the Soviet Union, Project Vanguard was put on hold briefly in favor of launching a satellite with Explorer 1. Vanguard 1 was the second artificial satellite put into orbit by the United States.

projective geometry: The study of geometric properties that do not change under projective transformation.

proportional counter: Proportional counters are instruments that detect the presence of an X-ray and measure its wavelength.

proton: A basic unit of all atoms made up of three fundamental particles called quarks. It has a positive charge equal to the negative charge on an electron and a mass 1800 times the mass of an electron. The nucleus of a hydrogen atom is a single proton.

pulsar: Scientists think that pulsars, pulsating radio sources with highly repeatable pulsation periods, are neutron stars of radius about 10 km and rotation period about 1 second. Their magnetic axis spins and beams radio waves, in a pattern similar to a lighthouse beam. We detect pulsars when the Earth is in the direction swept by the beam. Pulsars often emit X-rays and gamma rays as well.

Purdue University: Purdue University is a public, research university in West Lafayette, Indiana. It is a National Space Grant College with 52 other institutions that participate in space related research.

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quark: Quarks are fundamental building blocks for particles such as protons and neutrons.

quasar: Quasars (quasi-stellar objects) are the most luminous single objects we know in the Universe. They are found in the center of some galaxies, outshining their host galaxy in spite of their relatively small size (barely as large as our solar system). The central feature of a quasar is a massive black hole.

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radiation: A term used for phenomena that spread radially. In the narrow sense, some type of electromagnetic wave: radio, microwave, light (infra-red, visible or ultra-violet), X-rays or gamma rays are all types of electromagnetic radiation. Colloquially, an abbreviation of "ionizing radiation" meaning any spreading emission which can penetrate matter and ionize its atoms. That includes X-rays and gamma rays, but also high-energy ions and electrons emitted by radioactive substances, accelerated by laboratory devices or encountered in space (e.g. the "radiation belt" and "cosmic rays," also known as the "cosmic radiation").

radio waves: Radio waves have the longest wavelengths in the electromagnetic spectrum. Astronomical objects that have a changing magnetic field can produce radio waves.

radioactive decay: Instability of some atomic nuclei, causing them to change spontaneously to a lower energy level or to modify the number of protons and neutrons they contain. The 3 "classical" types of radioactive emissions are (1) alpha particles, nuclei of helium (2) beta-rays, fast electrons and (3) gamma-rays, high-energy photons.

redshift: An apparent shift of spectral lines to longer wavelengths, which can result from different physical causes. Motions of objects away from us create redshift. The expanding Universe produces galaxies with redshifted spectral lines, generally redshifts between 0 and 10. In the case of the binary stars, the redshifts are of the order of .001 to .0001. Astronomers have learned that the distance of an object can be directly inferred if the redshift is known. Motions of objects toward us create blueshift. Binary stars produce shifting spectra because of their orbital motion, which is alternately redshifted and blueshifted. (Binary star motions are called Doppler shifts.) Much of our knowledge of astronomy, for example, the masses of stars and distances to galaxies, is due to measurements of the redshift or blueshift of spectral lines.

reflectivity: The percentage of light that is reflected at a surface. Reflectivity depends on the material and wavelength of light.

refraction: The process in which the direction of light is changed as the result of a change in density of the medium it is passing through.

rest mass energy: The energy of a particle at rest.

Rice, Stuart: Stuart Rice is a Chemistry professor at the University of Chicago. He has worked in virtually every area of physical chemistry, from the theory of liquids, to molecular spectroscopy, to X-ray studies of surfaces.

Rice University: Rice University is a private research University in Houston, Texas. Along with 51 other institutions that are active in space related research, it is a National Space Grant College.

Richards, Paul: Paul Richards is a professor of physics at the University of California, Berkeley. His research focuses on infrared and millimeter wave physics, including the development of new detectors to solve scientific problems.

Ricker, George: An American astronomer and astrophysicist who was the Principal Investigator for the international High Energy Transient Explorer (HETE) mission - a small satellite incorporating instruments from France, Japan, and the U.S. - which was successfully launched on October 9, 2000.

Roman, Nancy: Nancy Roman is an American radio astronomer who was the head of the microwave spectroscopy division of the radio astronomy program at the Naval Research Laboratory. She eventually moved to NASA where she became the first Chief of Astronomy in the Office of Space Science.

Röntgen, Wilhelm Conrad (1845-1923): German physicist who first observed X-rays in the laboratory. Röntgen was experimenting with vacuum tubes when he noticed a fluorescent effect that should have not been possible due to the blockage of visible light by a cardboard cover. He suspected that a new type of invisible ray was responsible for the effect. Soon after, he would take the first X-ray image of his wife's hand, clearly showing her bones and wedding ring. Röntgen called the new type of rays "X-rays" to indicate that it is an unknown type of radiation. He would win the first Nobel Prize in Physics in 1901 for this discovery.

Roosevelt, Eleanor (1884-1962): Wife of President Franklin D. Roosevelt and longest-serving First Lady of the United States.

Roosevelt, Franklin D. (1882-1945): Franklin D. Roosevelt was the 32nd President of the United States.

Rossi, Bruno (1905-1993): An Italian-born, American physicist who worked at Los Alamos National Laboratory to support the development of the atomic bomb. He would later pioneer the rocket technology and experiments that enabled the measurements of interplanetary plasma and the discovery of the first source of extra-solar X-rays, Scorpius X-1. Additionally, he conducted experiments in his early career that would provide evidence of the decay of the muon. NASA's Rossi X-ray Timing Explorer (RXTE) was named after him, as is the Bruno Rossi Prize of the High Energy Astrophysics Division of the American Astronomical Society.

Royal Society of London: Founded in 1660, the Royal Society of London is a self-governing scholarly society whose purpose is to promote and support science.

Rutherford, Ernest (1871-1937): A New Zealand-born, British chemist who is best known as the father of nuclear physics for first putting forth the idea of the atomic nucleus.  He would be awarded the Nobel prize in Chemistry in 1908 for his work on the radioactive properties of the elements including the discovery of alpha and beta radiation, a number of new radioactive elements, and the development of his theory of radioactive disintegration of the elements.  His experiments would lead him to hypothesize the existence of the atomic nucleus which, according to Rutherford, contained the majority of the mass of an atom, as well as all of the positive charge.  Neils Bohr would build on Rutherford's theory to develop a model of the atom.

Russell, Henry Norris (1877- 1957): An American astronomer who spent most of his career at Princeton University. He is most well-known for work leading to the eventual Hertzsprung-Russel Diagram, a graph that measures a star's absolute magnitude against its temperature.

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sabbatical: A period of paid leave for a college professor to travel or study.

Sagan, Carl (1934-1996): An American astronomer who was well known for helping to popularize astronomy. He spent most of his career at Cornell University.

Sargent, Wallace (1935-2012): A British-born American astronomer and astrophysicist who was known for his studies of quasar absorption lines.

Schramm, David (1945-1997): David Schramm was an American astrophysicist. He spent his career at the University of Chicago and was well known for his work on dark matter and the study of Big Bang nucleosynthesis.

Schwarzschild, Martin (1912- 1997): A German-born American Astronomer. He was the head of the Stratoscope project in the 50s and 60s.

scintillation counter: A device that detects and measures ionizing radiation (particles).

scintillator: A material that, when excited by ionizing radiation, absorbs its energy and re-emits the absorbed energy in the form of light.

Scorpius X-1 (Sco X-1): Sco X-1 was the first cosmic X-ray source (other than the Sun) ever detected. It was discovered on June 18, 1962 by a team led by Riccardo Giacconi. His Aerobee rocket flight, launched to look for X-rays from the Moon, discovered Sco X-1. Aside from the Sun, it is the strongest source of X-rays in the sky. It was named for the constellation in which is it located, Scorpius.

serendipitous: When something happens by happy accident.

Seyfert galaxy: One of the types of active galaxies. Of the two type of Active Galactic Nuclei (AGN) which emit gamma rays, Seyfert galaxies are the low-energy gamma-ray sources. Seyfert galaxies typically emit most of their gamma rays up to energies of about 100 keV and then fade as we observe them at higher energies.

Shapley, Harlow (1885-1972): An American astronomer who served as the director of the Harvard College Observatory for more than 30 years.  After completing his PhD, he observed from Mount Wilson Observatory in California.  While at Mount Wilson, Shapley became interested in globular star clusters.  His study of globular star clusters and their distribution in space led him to correctly identify the center of the Milky Way Galaxy in 1918, an event which greatly increased human understanding of the size of the Galaxy and allowed him to calculate the position of the Sun in the Galaxy. In 1920 he would debate  Heber Curtis on the nature of the globular clusters; Heber Curtis thought that the nebulae were outside of our Galaxy and were in similar nature and size to our own Milky Way.  This even became known as the Great Debate. It was after this debate that he would be offered the directorship of the Harvard College Observatory.

shield: A blocking material on all but one side of the detector.

Iosif Shklovsky (1916-1985): A Soviet astronomer and theoretical astrophysicist. One of the things he is well known for was explaining some x-ray stars as binary systems that contained neutron stars.

shock wave: A powerful wave caused by a sudden change in density, pressure, or temperature that travels though a medium faster than sound travels through that same medium. source:

signal: In astronomy, the principle way we have to learn about the Universe is to study light. The light is collected in telescopes and focused on a detector. A detector, for instance, generates an electronic signature of the star: that signature is called the signal. All detectors generate some type of noise. The ratio of signal strength to detector or background noise determines the significance of the signal.

signal-limited: The detection of light involves the conversion of photons to electrons in some device and subsequent measuring of what is called a "signal". The term signal-limited implies that there is not enough light from a star: in a given period of time, the signal from an astronomical object hardly rises above the detector noise and the background from other sources. If one drives away from a radio station playing on the car radio, the signal from the station (the sound) and the signal is eventually lost in the static (the electronic background of the radio).

signal-to-noise: This ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is.

Simpson, John A. (1916-2000): John Simpson was an American physicist who did experimental work in nuclear and cosmic ray physics. He spent his career at the University of Chicago, teaching and doing research.

Smoot, George: George Smoot is an American astrophysicist and cosmologist at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory. He is most well known for the research on the cosmic microwave background for which he was awarded the 2006 Nobel Prize in Physics along with John Mather.

soft gamma repeater (SGR): Neutron stars with magnetic fields a thousand times stronger than ordinary neutron stars. Also known as magnetars.  The name derives from the fact that many bursts of gamma rays are emitted repeatedly from the same location. SGRs are probably due to starquakes on the surface of the neutron star. The quakes are so strong that they can break magnetic field lines, releasing a burst of gamma-ray energy. Originally confused with gamma-ray bursts, which only occur once at any given location (because afterwards, there is nothing left to continue to make more bursts).

soft X-ray: Low-energy X-rays, with energies between 0.1 keV and 10 keV.

solar eclipse: A solar eclipse occurs when the moon moves in front of the Sun as seen from a location on Earth. During a solar eclipse, the Sun dims as it is covered by the Moon. During a total eclipse, the entire Sun is covered for a few minutes and the sky darkens and the temperature drops.

solar flare: Violent eruptions of gas on the Sun's surface.

SONAR: A term that stands for SOund Navigation And Ranging. It’s a technique that uses sound waves to navigate, communicate or detect objects.

sounding rocket: In the early days of scientific uses of rocketry, sounding rockets were often used to probe conditions in the upper atmosphere, essentially “sounding” the upper atmosphere. Rockets carrying small payloads are thus called sounding rockets.

Space Race: A heated competition between the United States and the Soviet Union from 1957 to 1975 during which time each country tried to match or better the other's accomplishments in exploring outer space.

Space Science Board: The Space Science Board (SSB) of the National Academy of Sciences was appointed in spring 1958 at the request of the Executive Committee of the US National Committee for the International Geophysical Year (IGY). The Board's mission was to survey the scientific aspects of the human exploration of space. Accordingly, the SSB provided advice on the continuation and expansion of the IGY's rocket and satellite program, and later advised NASA, the Department of Defense, and the National Science Foundation on aspects of interplanetary probes and space stations, potential problems of manned spaceflight, the exploration of Venus and Mars, and other matters related to space.

space shuttle: NASA's space shuttle fleet first launched on April 12, 1981 and continued for 30 years of missions. Starting with Columbia and continuing with Challenger, Discovery, Atlantis and Endeavour, the spacecraft has carried people into orbit repeatedly, launched, recovered and repaired satellites, conducted cutting-edge research and built the largest structure in space, the International Space Station. The final space shuttle mission, STS-135, ended July 21, 2011 when Atlantis landed at NASA's Kennedy Space Center in Florida.

Space Telescope Imaging Spectrograph (STIS): In addition to taking detailed pictures of celestial objects, Hubble's Space Telescope Imaging Spectrograph (STIS) acts like a prism to separate light from space into its component colors. This provides a wavelength "fingerprint" of the object being observed, which tells us about its temperature, chemical composition, density and motion. Spectrographic observations also reveal changes in celestial objects as the Universe evolves. STIS spans ultraviolet, visible and near-infrared wavelengths.

Space Telescope Science Institute: Located in Baltimore, Maryland on the Homewood campus of Johns Hopkins University, the Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and the James Webb Space Telescope.

spectral waveband: A restricted region of wavelength generally narrower than the broader connotations of UV, IR, Optical, etc. Typically defined in optical systems by the properties of filters, gratings or other optical components.

spectrograph: An optical system that produces a spectrum, focused on a 2 dimensional detector, nowadays, an electronic detector with multiple pixels, read out all at once at the end of an exposure.

spectrometer: An optical system that produces a spectrum, which is then scanned with a photoelectric detector one wavelength at a time. Once a complete spectrum is available, which may require hours or days, the spectrum is made by plotting the points on a graph.

spectroscope: An optical system that produces a spectrum, which is then looked at through an eyepiece. The eyepiece scans along the spectrum to allow the astronomer to look at different wavelength regions. Spectroscopes have since been replaced with spectrometers and spectrographs.

spectroscopy: The creation and measurement of very small intervals of energy in the spectrum of a source.

spectrum: The number of photons, as a function of wavelength, that a source produces. The plural form of spectrum is spectra.

Spitzer, Lyman (1914-1997): Lyman Spitzer is best known for his original idea to put a large telescope in space. An astrophysicist who spent most of his academic life at princeton University, he was the first person to suggest a space telescope as a mechanism for avoiding atmospheric interference in astronomical observations and he shepherded.

Spitzer Space Telescope: Named for Lyman Spitzer, The Spitzer Space Telescope is the final mission in NASA's Great Observatories Program - a family of four space-based observatories, each observing the Universe in a different kind of light. Spitzer is designed to detect infrared radiation, or heat, which means its detectors and telescope must be cooled to only about 5 degrees above absolute zero (-450 degrees Fahrenheit, or -268 degrees Celsius). This will ensure that the observatory's "body heat" does not interfere with its observations of relatively cold cosmic objects. It is comprised of two major components: The Cryogenic Telescope Assembly, which contains the a 85 centimeter telescope and Spitzer's three scientific instruments and the Spacecraft, which controls the telescope, provides power to the instruments, handles the scientific data and communicates with Earth.

Sputnik: A series of small space satellites that were launched by the Soviet Union in the late 1950s. The first of these, Sputnik 1, launched by the Soviet Union on October 4, 1957, effectively started the national competition between the United States and the Soviet Union in space. The word Sputnik means satellite in Russian.

Stagg Field Stadium: The now demolished Stagg Field stadium was located on the campus of the University of Chicago and was used primarily for football games until the football program was discontinued in 1939. The site is now home to the University of Chicago’s Regenstein Library.

Stanford University: Stanford University is a private research university in Stanford, California. It was established in 1891.

star clusters: A group of stars. Star clusters can either be globular with hundreds of thousands of stars tightly bound or open, with less than a few hundred stars.

star quake: An astrophysical phenomenon that occurs when the crust of a neutron star undergoes a sudden adjustment, analogous to an earthquake on Earth. source:

star sensor: Telescopes in space have no solid platform to sit on. Without some form of navigation center, they would spin uselessly out of control. The stable Earth under a ground-based telescope makes the pointing of such a telescope easy. In space, a virtual platform must be set up. This is done with small cameras called star sensors. For a given point of a telescope to a spot in the sky, the position is found by demanding that when the telescope is in the right position, typically three sensors (usually side-looking) can each see a separate bright star. Once the correct object is acquired, an electronic guidance system automatically keeps the telescope pointing at the correct spot in the sky.

Josef Stefan (1835-1893): An Austrian mathematician and physicist best known for originating the Stefan-Boltzmann law, which establishes a constant relationship between a star's luminosity and its temperature . He was also a published poet.

stellar wind: The flow of neutral or charged gas ejected from the upper atmosphere of a star.

Stratoscope: Balloon-borne telescopes flown between 1957 and 1971. Martin Schwarzschild came up with the idea to build the stratoscopes.

Strong, Ian: A scientist at Los Alamos National Laboratory who discovered the first observed gamma-ray burst among the data from the Vela 4 satellites with his colleagues Ray Klebesadel and Roy Olson.

Stuhlinger, Ernst (1913-2008): Ernst Sruhlinger was a German-born American scientist. He studied atomic, electrical and rocket science. He was recruited to immigrate to the United States in the late 40s by the US Government.

supermassive black hole: "Supermassive" black holes are millions, if not billions, of times as massive as the Sun. Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies, even our own Milky Way. Astronomers can detect them by watching for their effects on nearby stars and gas.

supernova: The explosion of a dying, massive star results in a sharp increase in brightness followed by a gradual fading. The outer layers of the exploding star are blasted out in a radioactive cloud that is visible long after the initial explosion fades from view. The plural of supernova is supernovae or supernovas.

supernova remnant: A supernova remnant (SNR) is the remains of a supernova explosion. SNRs are extremely important for understanding our Galaxy. They heat up the interstellar medium, distribute heavy elements throughout the Galaxy, and accelerate cosmic rays.

supersonic: When something is traveling at rate of speed that is greater than the speed of sound. In dry, 68 degree Fahrenheit air at sea level, this speed is approximately 768 miles per hour.

survey: An examination and measurement of an area (such as the sky) for the purpose of documenting and describing its features.

Sutherland, Sir Gordon Brims Black McIvor (1907-1980): Sir Gordon Brims Black McIvor Sutherland was a Scottish physicist whose research included infrared spectroscopy. From 1956 to 1964 he was the director of the United Kingdom National Physical Laboratory. In 1964 he became Master of Emmanuel College, University of Cambridge.

Swarthmore College: Swarthmore is a liberal arts and engineering college southwest of Philadelphia in Pennsylvania.

Swift Gamma-ray Burst Explorer (2004-): The Swift Gamma-ray Burst Explorer, launched in 2004, is a multi-wavelength observatory carrying three instruments: the Burst Alert Telescope (BAT), the X-ray Telescope (XRT), and the Ultraviolet/Optical Telescope (UVOT). The primary scientific objectives of the mission are to determine the origin of gamma-ray bursts and to pioneer their use as probes of the early Universe. Swift is not an acronym; the telescope was named after a highly aerial small bird, the swift, because of the telescope’s ability to respond swiftly to a burst event. Swift can rapidly respond to newly detected GRBs and disseminate data. As soon as the BAT discovers a new GRB, Swift rapidly relays its 1-4 arcminute position estimate to the ground and triggers an autonomous spacecraft slew to bring the burst within the field of view of XRT and UVOT to follow-up the afterglow. Swift has provided redshifts for many bursts and multi-wavelength light curves for the duration of the afterglow. The BAT has also performed a high sensitivity hard X-ray sky survey.

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Tananbaum, Harvey: Dr. Harvey Tananbaum is director of the Smithsonian Astrophysical Observatory's Chandra X-ray Center (CXC). In this capacity he is responsible for overseeing of the operation of the Chandra X-ray Observatory and providing support to the scientific users of the observatory.

Technical University of Munich: The Technical University of Munich was established in 1868. It is a research University with campuses in Munich, Garching, and Freising-Weihenstephan, Germany.

telemetry: A technology that allows remote measurement and reporting of information. Although the term commonly refers to wireless data transfer mechanisms (e.g., using radio or infrared systems), it also encompasses data transferred over other media, such as a telephone or computer network, optical link or other wired communications.

Teller, Edward (1908-2003): A Hungarian-born, American physicist who was an integral member of the Manhattan project team which developed the atomic bomb.  After World War II and the detonation of the first atomic bomb, Teller would return to Los Alamos National Laboratory to work on the design for the hydrogen bomb, or "H-bomb".  Teller was also known as a co-founder with E. O. Lawrence of the Lawrence Livermore National Laboratory.

temperature: The measure of hotness or coldness of an object or substance.

Thaddeus, Patrick: Pat Thaddeus is a Professor Emeritus of Applied Astronomy at Harvard University. Thaddeus was part of a team that designed a radio telescope, the 1.2 meter Millimeter-Wave Telescope, that enabled astronomers to map large parts of the sky in short periods of time.

thesis: A document written by a candidate for an academic degree (bachelors, masters or doctorate) presenting the author’s research and findings.

Tousey, Richard (1908- 1997): Richard Tousey was an American astronomer. He was well known for taking the first photographs of the Sun’s UV spectrum using the V-2 rocket.

Townes, Charles (1915 - 2015): Charles Townes was a Nobel-prize winning physicist. In 1964 he shared the Nobel Prize in Physics with Nikolay Basov and Alexander Prokhorov for his pioneering work on the development of the maser. He was also known for his early use of masers and lasers in astronomy and was the first to calculate the mass of the supermassive black hole at the center of the Milky Way Galaxy. Additionally, he was the chairman of the NASA Science Advisory Committee for the Apollo lunar program from 1966 to 1970.

transformer: An electrical device that uses electromagnetic induction to transfer energy between two or more circuits.

Truman, Harry S. (1884-1972): Harry S. Truman was the 33rd President of the United States. President Truman served as Vice-President under President Franklin Delano Roosevelt, and was sworn in as president upon President Roosevelt's death in April 1945.

Two Micron All Sky Survey (2MASS): 2MASS was an infrared survey of the entire sky done between 1997 and 2001. The data was recorded at Mt. Hopkins in Arizona and the Cerro Tololo Inter-American Observatory in Chile and released in 2003.

type IC supernova: A category of stellar explosions caused by the core collapse of massive stars. These stars appear to have lost their entire outer envelope of hydrogen and most of their helium. As a result, Type Ic supernovae display different spectra than other categories of supernovae.

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ultraviolet (UV) extinction: Space is full of tiny dust particles. Those particles cause a dimming of the light from stars over the vast reaches of space. The dimming effect is much greater in the ultraviolet than in the optical. The dimming is normally referred to as extinction.

United States Naval Research Laboratory (NRL): The NRL is a corporate research laboratory for the United States Navy. It began operations in 1923. The NRL conducts a multidisciplinary program of scientific research and technological development and is funded through research and development grants from other government agencies.

University of Alabama Huntsville (UAHuntsville): The University of Alabama Huntsville is a public, state-supported university in the University of Alabama system. The other campuses in the system are located in Tuscaloosa and Birmingham, Alabama. UAHuntsville was founded in 1950.

University of Amsterdam: The University of Amsterdam is one of the largest general research universities in Europe. It has origins dating back to 1632. It is located in Amsterdam, North Holland in the Netherlands.

University of Arizona: The University of Arizona is a public research university located in Tucson, Arizona. It was founded in 1885.

University of Athens: Located in the Greek capital, the University of Athens was established in 1837. It is one of the largest state universities in Greece with about 125,000 students. 

University of California, Berkeley: The University of California, Berkeley is the flagship school in the University of California system. There are 10 campuses throughout California. Other campuses are located in Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, Santa Barbara and Santa Cruz. University of California, Berkeley was established in 1868.

University of California Santa Cruz (UCSC): The University of California Santa Cruz is part of the University of California system. There are 10 campuses throughout California. Other campuses are located in Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco and Santa Barbara. UCSC opened in 1965.

University of Cambridge: The University of Cambridge is a public research university located in Cambridge, England. It was established in 1209 and is the third oldest surviving university in the world.

University of Chicago: The University of Chicago is a private research university. It is located in Chicago, Illinois and was established in 1890.

University of Colorado, Boulder (CU-Boulder): CU-Boulder is a public research university. It the flagship university in the CU system and opened in 1877.

University of Manchester: A public research university located in Manchester, England. It was established 2004 when Victoria University of Manchester and the University of Manchester Institute of Science and Technology merged.

University of Michigan: The University of Michigan is a public research university located in Ann Arbor Michigan.

University of Milan: A research university in Milan, Italy. It was established in 1924.

University of Minnesota: A public research university located in Minneapolis and St. Paul, Minnesota. It was established in 1851.

University of Oxford: A research university located in Oxford, England in the United Kingdom. It is the oldest surviving university in the English-speaking world.

University of Rochester: The University of Rochester is a research university located in Rochester, New York.

University of Sussex: The University of Sussex is a teaching and research institution that was established in 1961. It is located in Falmer, East Sussex in England.

University of Toronto: The University of Toronto, previously King’s College, is a Canadian research university located in Toronto, Ontario.

University of Wisconsin-Madison: The University of Wisconsin-Madison is a public research university and is the flagship school in the University of Wisconsin system. It was founded in 1848.

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V-2 rocket: The V-2 rocket was the first ballistic missile, which is a missile that is only guided during the relatively brief initial powered phase of flight. Its course is subsequently governed by the laws of classical mechanics.

vacuum tube: A sealed glass tube containing electrodes from which the air has been evacuated. The electrodes control the flow of current within the tube. Vacuum tubes have since been replaced by solid state devices; the electrical components of the vaccum tubes were much bulkier and hotter than the solid state devices.

van Allen, James (1914-2006): James van Allen was an American space scientist. He spent his career at the University of Iowa. In 1958 he argued that Geiger counters should be added to the Explorer 1 and Explorer 3 satellite missions to detect charged particles. Subsequently, the radiation belts that were discovered were named after him (the Van Allen radiation belts).

van Paradijs, Jan (1946-1999): Winner of the Bruno Rossi Prize in 1998 for his work in finding the optical counterpart to a gamma ray burst, Dr. Jan van Paradijs was a Dutch scientist and member of the Burst and Transient Source Experiment Team (BATSE), a NASA project linked to the Compton Gamma-Ray Observatory.

van Speybroek, Leon (1935-2002): An American physicist known for his designs of X-ray telescope mirrors. van Speybroek joined Riccardo Giaconni at American Science & Engineering after receiving his PhD in nuclear physics from the Massachusetts Institute for Technology where he first became involved in mirror design for Skylab. He would later design the mirrors for the Einstein X-ray Observatory and Chandra X-ray Observatory. He received the Bruno Rossi Prize of the High Energy Astrophysics Division of the American Astronomical Society in 2002 for his contributions to X-ray optics.

Vanguard: The first American satellite program, Project Vanguard, was initiated to represent the United States in the 1957-1958 International Geophysical Year, a cooperative international scientific effort to study the physical properties of Earth. The Naval Research Laboratory was selected to develop the launch vehicle, called a Vanguard rocket, to carry a satellite into space. On October 4, 1957, the Vanguard team learned of the launch of Sputnik 1 by the USSR while still working on the second Vanguard test vehicle (TV2). About one month after the Soviet Union launched Sputnik 2, the United States made its first attempt at launching a satellite, Vanguard TV3, on December 6, 1957. TV3 exploded on the launch pad. On February 1, 1958, the United States successfully launched its first satellite, Explorer 1, using a rocket based on a design by Wernher von Braun. Then on March 17, 1958, the NRL Vanguard rocket successfully orbited the second American satellite, Vanguard-1. It was followed later by the launch of Vanguard-2 on February 2, 1959, and Vanguard-3 on September 18, 1959.

Vatican Observatory: An astronomical observatory in Castel Gandolfo, Italy that is run by the Catholic Church.

Vela Satellites: The first Vela satellite was launched in October 1963 by the United States Air Force to monitor the testing of nuclear devices in the atmosphere, which had recently been banned by the nuclear test ban treaty. The satellites monitored from space and never detected clandestine nuclear explosions, instead finding burst of gamma rays coming from deep space.

Very Energetic Radiation Imaging Telescope Array System (VERITAS): The Very Energetic Radiation Imaging Telescope Array System (VERITAS), located near Amado, Arizona, is an array of 4, 12-meter optical telescopes built to study gamma rays from extreme astrophysical phenomena in the Universe. To detect astrophysical gamma rays in this so-called very high energy regime requires a ground-based method of detecting gamma-rays by observing the Cherenkov light emitted by showers of particles produced when the gamma-rays interact in the Earth’s atmosphere. In 2004, VERITAS began scanning the night sky searching for remnants of exploded stars, distant active galaxies, gamma ray bursts, and evidence of dark matter.

Very Large Telescope (VLT): The VLT is one of the telescopes operated by the European Southern Observatory in Chile. It is made up of four optical/infrared telescopes that can work together to achieve very high angular resolution.

Villard, Paul (1860-1934): French physicist working in Paris at the same time as Marie and Pierre Curie, he is credited with discovering gamma rays. Villard's main interest was chemistry, which guided him into his studies of cathode rays, X-rays, and "radium rays.” His experiments in radioactivity led to the unexpected discovery of gamma rays in 1900. Villard recognized them as being different from X-rays because the gamma rays had a much greater penetrating depth. He discovered they were emitted from radioactive substances and were not affected by electric or magnetic fields. These rays came to be called gamma rays by another scientist, Ernest Rutherford. In 1914 Rutherford showed that they were a form of electromagnetic energy with a much shorter wavelength than X-rays.

visible light: Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.

von Braun, Wernher (1912–1977): Dr. Wernher von Braun was the first director of the Marshall Space Flight Center. From childhood, he was fascinated with rockets and space flight. He helped to develop the deadly V-2 rocket during WWII, but later turned his skills to the development of the Saturn rockets, which would eventually bring man to the Moon.

Voyager Program: Voyager 1 and Voyager 2 are unmanned space probes that were launched in 1977 to study the planetary systems of Jupiter and Saturn.

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Wallops Island: A small island off the Eastern Shore of Virginia. The island is primarily used for NASAs Wallops Flight Facility which is a center for aeronautic research.

water ice: Ices are mixtures of H, C, N and O that exist in a frozen state. Water ice is the familiar type based on H2O molecules in a solid state. Another type of ice is ammonia ice, made of NH3.

water vapor: Water in its gaseous state.

wavelength (λ): The distance between two crests of a propagating wave of a single frequency (f). If v is the velocity at which the wave advances, v=fλ, or velocity equals frequency times wavelength.

Werner, Mike: Mike Werner is the Project Scientist for the Spitzer Space Telescope and the Chief Scientist for Astronomy and Physics at the Jet Propulsion Laboratory at the California Institute of Technology. His research focuses on infrared astronomy, specifically star formation, the interstellar medium, and the central regions of our Galaxy.

Westinghouse Science Talent Search: The Science Talent Search, a program of Society for Science & the Public, is a prestigious science research competition for high school seniors. Since 1942, first in partnership with Westinghouse and beginning in 1998 with Intel, SSP has provided a national stage for young scientists to present their original research to nationally recognized professional scientists.

Wheeler, John (1911- 2008): John Wheeler was an American theoretical physicist. He is well known for coining the terms “black hole” and “wormhole.” He spent most of his career at Princeton.

white dwarf: A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's. This gives a white dwarf a density about 1 million times that of water.

White Sands Missile Range: The largest overland military test range in the United States, occupying some 3,200 square miles of southern New Mexico. First known as White Sands Proving Ground (renamed White Sands Missile Range in 1958), this installation was established on July 9, 1945, as the place to test rocket technology emerging from World War II.

White Sands, New Mexico: White Sands is located in southern New Mexico and is home to the largest gypsum dune field in the world. White Sands Missile Range began operations in 1945 and is located within the dune field.

Wide-Field Infrared Survey Telescope (WFIRST): The Wide-Field Infrared Survey Telescope (WFIRST) is a NASA observatory designed to perform wide-field imaging and slitless spectroscopic surveys of the near infrared (NIR) sky for the community.

Wilson, Robert (1914-2000): An American physicist and astronomer who, along with Arno Penzias, accidentally discovered cosmic microwave background radiation (CMB) while they were working as researchers at AT&T Bell Laboratories. CMB was the "smoking gun" in favor of the Big Bang Theory.

Woody, David: David Woody is the Assistant Director of the Owens Valley Radio Observatory (OVRO) of the California Institute of Technology. At OVRO he leads instrument development and has played a role in the development of the Owens Valley millimeter-wave array and the Combined Array for Research in Millimeter-Wave Astronomy (CARMA).

Woosley, Stanford (Stan): An astrophysicist at the University of California, Santa Cruz. He is also the director of the Center for Supernova Research at UCSC. A high-energy astrophysicist, his research focuses on astronomical phenomena such as supernovae and gamma-ray bursts. He is a co-investigator for the High Energy transient Explorer 2 (HETE-2) . He received the Bruno Rossi Prize in 2005.

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Yale University: Yale University is a private, research university located in New Haven, Connecticut. It was founded in 1701 and is the third oldest university in the United States. The undergraduate school is called Yale College.

Yerkes Observatory: Yerkes Observatory is a facility of the University of Chicago’s Department of Astronomy and Astrophysics. It was established by George Ellery Hale in 1896 and houses what is still the largest refracting telescope in the world (40 inches). The observatory is located near Lake Geneva in Williams Bay, Wisconsin.Yerkes Observatory is a facility of the University of Chicago’s Department of Astronomy and Astrophysics. It was established by George Ellery Hale in 1896 and houses what is still the largest refracting telescope in the world (40 inches). The observatory is located near Lake Geneva in Williams Bay, Wisconsin.

York, Donald: Donald G. York is an American astronomer at the University of Chicago. He has worked all his life on the gas and dust between the stars and between the galaxies, starting with the Copernicus UV satellite-spectrometer, but more recently with the Sloan Digital Sky Survey, of which he was the founding director.

York, Herbert (1921-2009): Herbert York was an American physicist best known for his outspoken opinions about arms control. He worked with the Manhattan Project, focusing on the electromagnetic separation of uranium 235, and later became director of the Lawrence Livermore Laboratory. In 2000, he received the Enrico Fermi award in recognition of his contributions to nuclear deterence.

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z: Also called redshift, z. is the ratio of the observed change in wavelength of light emitted by a moving object to the rest wavelength of the emitted light. This ratio is related to the velocity of the object. Objects at the furthest reaches of the known Universe have values of z = 5 or slightly greater.

Zwicky, Fritz (1898- 1974): Fritz Zwicky was a Swiss astronomer who spent his career at the California Institute of Technology. He made many contributions to astronomy including work on gravitational lenses and dark matter.