1. Chapter 2: Patterns in the Sky – Motions of Earth

2. Looking around the sky: What are the Constellations?

3. Every culture has their own constellations So whose constellations do astronomers use?

4. 88 Official Constellations Andromeda Established by the IAU in 1922 with boundaries finalized in 1928

5. What you see at night depends on what time it is If it’s clear, go out tonight sometime and note the locations of the bright stars. Do the same thing two or three hours later to see how things have moved

6. What you see at night depends on what month you look Looking south in July Looking south in January

7. What you see at night depends on where you are Cerro Tololo Chile

8. Why does the sky change during the course of a night? The Earth rotates about its’ polar axis so the stars make circles around the celestial pole.

9. Why does the sky change over the course of a year? As we orbit the Sun, the direction opposite the Sun changes and we only see the stars that are on the opposite side of Earth from the Sun

10. Why does the sky change with your location? As you move away from the pole your horizon moves with you but the locations of the celestial poles and celestial equator remains the same

11. The Earth moves in two ways that affect what we see Orbital motion around the Sun causes seasonal changes in the constellations Rotational motion around the polar axis causes changes over the course of the night

12. The Celestial Sphere Model We know the universe doesn’t rotate around us but it can be useful to imagine that it does

13. The Celestial Sphere can be used to explain the daily motions and the changes due to location