AST 101 Lecture Notes - Lecture 4: Celestial Spheres

• School: Syracuse University
• Department: Astronomy
• Course: AST 101
• Professor: Walter Freeman

Document Summary

We can treat the stars as all rotating together, on an invisible sphere far away. We expect this to get the stars right (things that are really far away) and the planets and sun wrong (things that are closer) The axis of rotation ins the same as the earth"s, and it rotates once per day. Only half of the sphere is visible because earth is in the way. Remember, the celestial sphere"s apparent rotation is backwards from this. Stars/planets/sun rise in the east and set in the west. Set: falling out of visibility below the horizon. Circumpolar: rotating around a celestial pole without setting (i. e. polaris) The celestial sphere turns counterclockwise! (rising in east and setting in west) Over the course of one day, the earth doesn"t move very much. This means the celestial sphere model can show us how the sun moves each day.