Lecture05 - Lecture #5: Earth, Moon, & Sky II The Main...

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1 Astro 102/104 1 • Lunar Phases and Motions. Lunar Phases and Motions. • Tides. Tides. • Eclipses. Eclipses. Astro 102/104 2 The Main Point The Moon’s size and orbit lead to many interesting phenomena: changing phases, tides, and eclipses. Astro 102/104 3 Phases and Motions of the Moon • The Moon orbits the Earth in an inclined (~5°) and slightly elliptical (0.055) orbit about 60 Earth radii away. • The Moon's appearance in the sky (its phase ) changes considerably as it orbits the Earth. – The result of changing illumination by the Sun. Astro 102/104 4
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2 Astro 102/104 5 • The sidereal period is measured wrt the background stars. • The Moon's sidereal orbital period is 27.3 days. • But because of the Earth's motion around the Sun, it takes ~29.5 days (a lunar month or synodic month ) for the Moon's phases to repeat. Sidereal and Synodic Periods Astro 102/104 6 Is the Moon Spinning? •Yes! • But then why do we see the same features all the time? • Try the following experiment to prove it to yourself: Without spin With spin Astro 102/104 7 Day and Night on the Moon • The Moon is in synchronous rotation with the Earth: – Spin period = Orbital period. – One lunar "day" = One lunar month.
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This note was uploaded on 03/04/2008 for the course ASTRO 1102 taught by Professor Squyres,s/margot,j during the Spring '07 term at Cornell.

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Lecture05 - Lecture #5: Earth, Moon, & Sky II The Main...

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