1. CONSTELLATIONS

2. WHAT are they? When we look into the night sky, it appears that everything is attached to the “dome” of the sky.

3. Astronomers call the sphere that appears to circle the earth the celestial sphere.

4. Eudoxes, 400BC The earth was viewed as surrounded by an orbiting crystal sphere, in which were carried the stars, sun, moon.

5. Crystal sphere model, ca. 300BC

6. Stars-- Were all seen as the same distance away, on the same sphere.

7. constellations • Are patterns early “astronomers” saw in the night sky.

8. Useful? • In earlier historic periods, constellations helped people find key stars, which were used in navigation.

9. Ursa Major

10. In modern astronomy… • Constellations define an area of the celestial sphere

11. Ursa Major’s area

12. Useful? • In this way we can refer to an object’s (planet, comet, satellite) position as being “in” a constellation.

13. e.g., “mercury is in ursa major”