AST 1002 Lecture Notes - Lecture 1: Minute And Second Of Arc, Trade Union Confederation Of The Americas, Aswan
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Earth is a rocky sphere, 3rd rock from an average star: the sun. How many stars can you see with your naked eye: ~6000. 1 meter (m) = 1 yard (3. 3 feet, 40 inches) Speed of light: 3. 0*10^5 km/s=186,000 miles/s (cid:862)co(cid:374)stellatio(cid:374)s(cid:863): (cid:272)ha(cid:374)(cid:272)e alig(cid:374)(cid:373)e(cid:374)ts of stars. Useful for na(cid:448)igatio(cid:374), calendar, naming locations in the sky, mythology. Stars and planets look like points of light o(cid:374) the (cid:862)celestial phere(cid:863) Fixed patterns move across the sky because the earth rotates once per day. Stars appear to rotate around the north celestial pole. Each day the earth rotates the sun . 986 degrees. Sidereal day= 1 actual earth rotation relati(cid:448)e to dista(cid:374)t (cid:862)fi(cid:454)ed(cid:863) stars. Solar day: 1 earth rotation relative to sun. Different stars are visible at different times of year because of the earth rotating around the sun. As we orbit the sun, night occurs facing different directions. Long term changes: earth precesses like a top, making a full cycle every ~27,000.
