Miscellaneous announcements…• Get started on your first observing project.

• Anyone interested in the astrophotography project?

• No class Monday (happy Labor Day).

• First homework is due Wednesday.

The Stars from Different Latitudes

1 September 2006

Today:

• How the stars change as you move to different latitudes on earth

• Using the stars to measure the size of the earth

From other locations…

• Longitude (E-W location) doesn’t matter, except to determine time of day

• Latitude matters: For every 70 miles traveled north, northern stars get 1º higher, southern stars 1º lower

• So a 360º shift would presumably take 360 x 70 miles, or 25,000 miles: the earth’s circumference!

The Two-Sphere Universe

• The earth is a much smaller sphere at the center of the celestial sphere.

• As you move around on the earth, your horizon changes orientation so you see a different half of the celestial sphere.

• This model dates back to ancient Greece, 2500 years ago.