ASTR 101 Lecture Notes - Lecture 3: Apparent Retrograde Motion, Lunar Phase, Ecliptic
30 Oct 2017
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Why do we see phases of the moon?--> lunar phases are the consequence of the moon"s 27. 3 day orbit around earth. Phases of the moon: half of moon is illuminated by sun and half is dark, we see a changing combination of the bright and dark faces as moon orbits. We only see one side of the moon: synchronous rotation: the moon rotates exactly once with each orbit, that is why only one side is visible from earth. When either passes through the others shadow we have an eclipse: moon passes entirely through umbra (total lunar eclipse, part of the moon passes through umbra (partial lunar eclipse, moon passes through the penumbra (penumbral lunar eclipse) When can eclipses occur: solar eclipses can occur only at new moon, solar eclipses can be total, partial or annular (ring around) Two conditions for a solar eclipse: must be a full moon ( for lunar) or new moon (for solar eclipse)
