A

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

altitude: The height of something above the ground.

ancestors: The people from whom one is decended.

antennae: A wire or set of wires that transmits or receives radio signals.

asteroids: A rocky space object which can be from a few hundred feet to several hundred km wide. Most asteroids in our solar system orbit the Sun in a belt between Mars and Jupiter.

astronomer: An expert in the study of the Sun, Moon, stars, planets, and other space bodies.

atmosphere: The gas that surrounds a planet or star.

atom: Very small particles that all matter visible is made of. Atoms combine with each other to form molecules. Atoms are made of protons, neutrons and electrons.

B

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

Brahe, Tycho (1546-1601): Tycho Brahe (a.k.a Tyge Ottesen) was a Danish astronomer whose accurate astronomical observations of Mars in the last quarter of the 16th century formed the basis for Johannes Kepler's laws of planetary motion.

C

celestial: Of or pertaining to the heavens.

comets: Frozen masses of gas and dust which have a definite orbit through the solar system.

Congress: The branch of the United States government that makes laws.

Copernicus, Nicolaus (1473-1543): Nicolaus Copernicus was a Polish astronomer who advanced the theory that the Earth and other planets revolve around the Sun (the "heliocentric" theory). This was highly controversial at the time, since the prevailing Ptolemaic model held that

cosmos: Having to do with the study of the history, structure, and changes in the universe.

D

data: of information such as facts, statistics, or measurements that can be collected and studied.

deploy: To be made ready to use.

detector: A sensor; the component of an instrument that converts a radiation signal (collected, for instance, by a telescope), into a quantity which is measured by another part of the instrument (usually, electronic equipment).

deuterium: A heavy isotope of hydrogen having one proton and one neutron in the nucleus.

diffraction grating: A substrate with closely spaced rulings (reflecting surface or a transmission grid). Light hitting a grating is dispersed into a spectrum (as, in the optical part of the spectrum, the colors of a rainbow.)

E

electromagnetic: Of or pertaining to magnetism produced by or associated with electricity.

electron: The negatively charged part of an atom, of a size about 1/1800 of the proton (the postive charge-carrying componet of an atom).

elements: A substance which cannot be broken down by ordinary chemical means into simpler components.

emit: To produce light, or more generally, electromagnetic radiation.

energy: Usable heat or power; in physics, it is the capacity of a physical system to perform work.

Extra-Terrestrial: Originating from or existing outside the Earth.

F

fleet: A large group of vehicles, planes or ships owned by the same organization.

G

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 the Moon and

gravity: A mutual physical force attracting two bodies.

gyroscopes: A spinning wheel set in a movable frame.

H

helium: The second lightest and second most abundant element. The neutral helium atom consists of a nucleus of two protons and two neutrons surrounded by two electrons. Helium was first discovered in our Sun. Roughly 25% of the mass of our Sun is helium.

Herschel, Sir William (1738-1822): William Herschel was 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, and cataloged stars and

horizon: The line where the earth and the sky appear to meet.

Hubble, Edwin P (1889-1953).: Edwin Hubble was an 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

Hubble Space Telescope (HST): A large telescope placed in orbit above Earth in 1990 that takes pictures of objects in space. It was named for Edwin Hubble. Being above the atmosphere of Earth, it is capable of recording exquisite pictures.

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

I

infrared: Electromagnetic radiation with long wavelengths which is found in the invisible part of the spectrum, redward of the visible part. Human beings experience infrared waves as heat.

J

K

Kepler, Johannes (1571-1630): Johannes Kepler was aGerman astronomer and mathematician. Considered a founder of modern astronomy, he formulated the famous three laws of planetary motion. They comprise a a more exact and quantitative formulation of Copernicus's theory that

L

latitude: A measurement of distance, given in degrees north or south from the equator.

light: The common term for electromagnetic radiation, usually referring to that portion visible to the human eye. However, other bands of the e-m spectrum are also often referred to as different forms of light.

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.

Lippershey, Hans (1570-1619): Hans Lippershey was a German-Dutch eyeglass maker who was the first person to apply for a patent for a telescope.

longitude: A measurement of distance, given in degrees east or west of the prime meridian. The prime meridian is a line that runs through the Greenwich Observatory in London, England. On a map or globe, lines of longitude are drawn from the North Pole to the South Pole.

M

marginal: The very minimum to meet requirements.

matter: A word used for any kind of stuff which contains mass.

Melvill, Thomas (1726- 1753): Thomas Melvill was a Scottish physicist who was active in the field of spectroscopy.

micrometer: An instrument used with a telescope that measures very small distances or angles.

Milky Way: The galaxy to which the sun belongs.

N

narrow slit prism: A form of spectrograph in which the prism accepts light only from a narrow slit, to prohibit blurring of the image.

nebulae: A low density cloud of gas and dust in which a star is born. Also, a historical name for fuzzy patches in the sky, before the existence of galaxies was understood.

Newton, Isaac: Sir Isaac Newton (1643-1727) was 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.

O

observatory: A building that houses a telescope. More generally, a place with many telescopes, whether mounted in buildings or not.

orbit: The path of an object that is moving around a second object or point.

ozone: An almost colorless, gaseous form of oxygen with an odor similar to weak chlorine.

P

Parsons, William (1800-1867): William Parsons, 3rd Earl of Rosse was 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.

phenomenon: Something that can be observed that may be hard to understand.

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).

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.

Q

quasar: A distant luminous energy source which gives off vast amounts of radiation, including radio waves and X-rays. Thought to be powered by black holes and to reside at the center of most galaxies.

R

reflecting telescope: A telescope which collects light by means of a (ususally) concave mirror.

refracting telescope: A telescope which collects light by means of a lens or system of lenses. Also called “a refractor”.

refracts: 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.

Ritter, Johann (1776 - 1810): Johann Ritter is credited with discovering and investigating the ultraviolet region of the electromagnetic spectrum.

S

spectrograph: The image of the electromagnetic spectrum produced by a spectroscope.

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.

sub-nuclear particle: Particles smaller that make up protons and neutrons: quarks, for example.

supernova: The explosion of a dying, massive star results in a sharp increase (hours to days) in brightness followed by a gradual fading (over months). 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.

T

telescope: Any of various devices, sometimes made with an arrangement of lenses, mirrors, or both, used to detect and observe distant objects by their emission, transmission, reflection, or other interaction with invisible radiation.

titanium: A chemical element with symbol Ti and atomic number 22. It is a transition metal of low density and high strength.

U

ultraviolet: Electromagnetic radiation at wavelengths shorter than the violet end of visible light; the atmosphere of the Earth effectively blocks the transmission of most ultraviolet light.

V

W

wavelength: The distance between one peak or crest of a wave of light, heat, or other energy and the next peak or crest.

X

Y

Z

zenith: The point of the celestial sphere directly overhead, 90 degrees above the horizon, for any point on Earth; it is the point where a plumb line extended upward would intersect the celestial sphere.