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.