ASTR 207 Study Guide - Quiz Guide: Sidereal Year, Observable Universe, Analemma

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Stars in the milky way: 100 billion. Galaxies in the observable universe: ~100 billion (within a factor of. To the nearest star: 4 light years (alpha centauri) To the nearest galaxy: 2. 5 million light years (andromeda) From sun to outermost planet: 30 au (neptune) From sun to centre of milky way: 27 000 light years. From sun to asteroid belt: 3. 2 au. Milky way: 100 000 light years (across) Sun: 2. 0 x 10^30 kg: sidereal day - 23h56m07s. Earth completes one rotation on its axis: solar day - 24h. Sun makes one circuit around the sky: sidereal month - 27. 3 days. Moon completes one cycle of lunar phases (1/12 longer than a sidereal month: sidereal year - 365. 26 days. Earth completes one orbit around the sun: tropical year - 365. 24 days. Counted from one summer solstice to the next: planetary periods - can be measured relative to apparent position of.

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