Motions1

# Motions1 - Precession is SLOW (about 26,000 years) to go...

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Motions The motion of the stars is really motion of the Earth. We observe three basic motions when we observe the night sky: a very long term drift of the north celestial pole . .....  from wobble in Earth's  rotation daily motions . ........  from Earth rotating (spinning) on it's axis yearly motions . .......  from Earth revolving (orbiting) around the Sun We will examine each of these motions in more detail. Motions: precession (This is out of order - taken from Chapter 5 p. 174-175 or 2nd ed. Ch. 4 p. 148) Earth wobbles as it spins - much like a top does. (The precession (wobble) is caused by the Sun and Moon's gravities acting on the  bulge of the Earth and by the conservation of angular momentum. We will talk more  about these concepts later.) One result of precession is that we will have a different "North Star" in the future.

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Unformatted text preview: Precession is SLOW (about 26,000 years) to go around once. Motions: daily motion arise from the rotation (spin) of Earth causes the rising and setting each day of the Sun, Moon and stars If nothing else moved . ....... then motions are simple. The sun would rise at the same time every day ! But . .... Earth is also moving around the Sun. => it takes a little more than one full rotation of Earth for Sun to rise again. So how long is a day ? • sunrise to sunrise ? . .................. = "solar day" • one rotation of the Earth (with respect to the stars) ? . ....................... = "siderial day" "siderial" = with respect to the stars Average solar day is about 4 minutes longer than the siderial day....
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## This note was uploaded on 03/09/2012 for the course AST 1002 taught by Professor Emilyhoward during the Spring '10 term at Broward College.

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Motions1 - Precession is SLOW (about 26,000 years) to go...

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