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Earth Moon Sun! Earth! ecliptic Mercury! Mars! plane! Moon s orbit is only slightly tilted out of ecliptic plane! Earth – Sun Distance = 1 Astronomical Unit (AU)! Venus! Looking down onto (north) inner Solar System — all planets orbit Sun counterclockwise (not to scale)! horizon! How does being in the ecliptic affect where we see the planets in the sky from the ground, on Earth?! This is the whole Solar System:! ecliptic saturn! mars! venus! horizon! Sun! Sun, planets look as if they re in a gentle arc — the ecliptic! 25,000 AU = 5 light-MONTHS! 40 AU = 5.5 light-hrs! Oort Cloud! Polaris — 330 l-yr — 1 billion times farther from Earth than the Sun Sun, planets, Kuiper belt! North spin axis! South spin axis! orbits of comets in Oort Cloud are like bees swarming around a hive! to Polaris spin axis! North! equator! equator — defined as being at right angles to the spin axis! South! Earth 23" °! earth's precession causes the exact location of the equinoxes to move a little each year Earth Moon Sun! MOVIE: Precession ecliptic plane! Moon s orbit is only slightly tilted out of ecliptic plane! Earth – Sun Distance = 1 Astronomical Unit (AU)! earth np earth moon sunlight moon sunlight np We see different parts of the moon illuminated over the course of the month. This phenomenon is referred to as sunlight the Phases of the Moon. Why do we see the Moon in phases? Beause it moves between us and the Sun. Everything that moves between us and the Sun we will see in phases.