ASTA01H3 Lecture Notes - Lecture 2: Axial Tilt, Libration, Angular Diameter
Document Summary
Asta01- chapter 2 user"s guide to the sky: patterns and cycles. Lecture 03: more than 2100 years ago, astronomer hipparchus compared a few of his star positions with those made by other astronomers nearly two centuries before him. He realized that the celestial poles and equator were slowly moving relative to the stars. Later astronomers understood that this apparent motion is caused by a special of earth called precession. If you have ever played with a toy top or gyroscope, you may recall that the axis of such a rapidly spinning object sweeps around relatively slowly in a circle. The weight of the top tends to make it tip. This combines with its rapid rotation to make its axis sweep around slowly in precession motion: earth spins like a giant top, but it doesn"t spin upright relative to its orbit around the sun.
