Motion of the Stars

Purpose: To demonstrate how latitude determines which stars are viewable in the sky

Key Concepts: The apparent rise and set motion of the stars is a result of Earth's rotation. To demonstrate visible stars differ at from different latitudes.

Prior knowledge for this lesson: Students should have some familiarity with geography, lines of latitude, with a globe, and cardinal directions.

Material:
Home planetarium
Laser pointer
List of bright stars and well-known constellations
Slide projector, PowerPoint
Slides of:
World map with latitude
Earth with equator and axis
Earth/globe

Glossary:
Circumpolar - revolution around the pole star
Constellation - grouping of stars that form a pattern marking a certain area in the night sky
Equator - invisible line at 0 degrees latitude that divides the Earth into the north and south hemispheres
Hemisphere - half of a circle
Horizon - lowest point of the sky, where the sky meets the earth
Latitude - an imaginary line joining points on the Earth's surface that are all of equal distance north or south of the equator.
Polestar - Polaris, North Star, star that appears not to move because it is aligned with the Earth's axis
Rotate - to spin on an axis
Revolve - to move on a path around an object
Zenith - the sky just overhead

Room preparations: Label the cardinal directions on the walls so that you can refer to them when you are telling students where to look. Designate the bottom of the window or molding on the walls as the horizon. This lesson will require a darkened room to project the stars on the wall and slides.

Procedure:
1. Show on globe that Earth revolves around and invisible axis (point to the north and south pole and spinning the globe) and the Earth's axis points towards the North Star (Use laser pointer and point to the north star).
2. Explain that the equator divides the Earth into north and south hemispheres and that lines of latitude tell your position on Earth; how far north and how far south you are from the equator.
3. Explain that the stars are always present but the Sun's light obscures the stars in the day. Explain that as the Earth spins, it gives the illusion that the Sun and stars appear to rise in the east and set in the west (Demonstrate using the planetarium how stars appear to revolve around the room).
4. Explain to that not all stars are visible from all locations that the stars visible in the northern hemisphere are too low in the sky to be viewed from the southern hemisphere and vice-versa. Using the North Star, demonstrate where it would appear if we were looking at it from the north pole (90 degrees N), from Chicago (42 degrees N), from the equator (0 degrees) and from South Africa (30 degrees S) noting the corresponding latitudes.
5. Go back to the North Pole position with the North Star at the zenith. Explain and demonstrate that someone watching the stars from the North Pole will never see any stars rise from or set below the horizon. The stars appear to rotate around the North Star.
6. Go to the Chicago position and explain and demonstrate that from Chicago, some stars set and stars still appear to revolve around the North Star however, there are some (Big Dipper, Cassiopeia etc.) that never appear to set.
7. Go to the Equator position and explain and demonstrate that all stars appear to rise and set and instead of stars appearing to revolve around the North Star; they now appear to revolve around you.
8. Go to the South Africa position and explain and demonstrate that most of the stars that were visible in the northern hemisphere are no longer visible from this location. Point out that from this position, stars appear to revolve around the Southern Cross?

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