1. Miscellaneous announcements… Course web site is up to date with all handouts and Homework 1 solutions. Start planning your two observing projects. Questions on course policies?

2. Motions of the Stars 30 August 2006

3. Course Outline Naked-eye astronomy Crash course in physics Our solar system The stars Structure and history of the universe

4. Course Outline Naked-eye astronomy Crash course in physics Our solar system The stars Structure and history of the universe You are here

5. Today: How the stars appear to move through our sky each night (facing N, S, E, W) How this motion depends on your location on earth (and how to measure the earth’s size using the stars) A simple (but incorrect) model to explain this motion

6. Star trails in east

7. Star trails in west

8. Star trails in south

9. Star trails in north

10. Summary (for mid-northern latitudes) Most stars rise in east, set in west Rising stars head toward the south, setting stars come from the south In southern sky, stars move left to right In northern sky, stars make CCW circles around the north celestial pole Star patterns don’t change in size or shape

11. To remember all these facts… Pretend that the stars are all pasted on the inside of a giant rigid sphere, with us at the center. The sphere is spinning around, about once every 24 hours. The rotation axis points through us along a diagonal, up and to the north.

12. Star trails in north

13. 19 degrees 75 minutes / 19 degrees = 4 minutes per degree

14. Rate of motion A full circle is 360º Stars move 1º in approximately 4 minutes 15º in 60 minutes (one hour) 360º in 24 hours (approximately)

15. More precisely… Stars actually move about 361º in 24 hours 360º takes only 23 hours, 56 minutes Therefore eastern stars appear a bit higher each night; western stars appear lower (at any given time of night) But in 360 days (actually 365.24), these 1º offsets will add up to a full circle

16. For practice: www.skyviewcafe.com (linked from course web page)www.skyviewcafe.com Skychart III (free download) Low-tech “planisphere” (purchase or download and print)