Motion of the Moon
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Transcript of Motion of the Moon
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Motion of the Moon
Lecture 5
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3-1 Why we see the Moon go through phases
3-2 Why we always see the same side of the Moon
3-3 The differences between lunar and solar eclipses
3-4 Why not all lunar eclipses are total eclipses
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lunar phases = different appearances of the Moon
What is causing the phase of the Moon?
Common mis-conception = shadow of the Earth
Phase of the Moon
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On its way to Jupiter, the Galileo spacecraft took a picture of Earth + Moon. In this image, Earth and Moon showed the same phase.
if the shadow of the Earth was causing the phase of the Moon, why the Earth also showed the same phase?
Image taken by Galileo spacecraft in 1992
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Why the Moon goes through phases
relationship b/w lunar phases and Moon’s positions in its orbit
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Have you ever noticed that, on a clear dark night, you can not only see the bright-side of the Moon but also the dark-side of the Moon?
What is this?
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Because the Earth shines the un-illuminated side of the Moon known as Earthshine.
Earthshine
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Moon’s synchronous rotation
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Moon’s synchronous rotation
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sidereal month : time takes the Moon to complete one full orbit of Earth w.r.t. distant stars (27.32 days)
synodic month : time takes the Moon to complete one cycle of phases (29.53 days)
Sidereal and Synodic Months
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When Sun, Earth, and Moon are all aligned to a straight line, an eclipse happens.
Earth-Moon-Sun solar eclipse Moon blocks the Sun
(always new Moon)
Moon-Earth-Sun lunar eclipse Shadow of Earth blocks the Moon
(always full Moon)
Why aren’t there lunar/solar eclipses every synodic months?
Eclipses
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Due to the changing apparent sizes of the Sun and Moon, we see different types of eclipses (especially solar eclipses). these changing angular diameters are due to elliptical orbits of the Earth and Moon.
Sun’s angular diameter : 31.’6—32.’7Moon’s angular diameter : 29.’3—34.’1
Different eclipses
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Conditions for Eclipses
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Total Lunar Eclipse Nine photographs over 3 hours during the total lunar eclipse of Jan 20, 2000. Lunar eclipses can be seen nearly all across the world (why?)
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Three types of lunar eclipses
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In summary…
Important ConceptsMoon’s phase and time if its
visibilities relative to the SunSynchronous rotation of the MoonMechanism of eclipse
Important Termslunar phasesidereal monthsynodic monthEarthshineline of nodesumbra and penumbra
Chapter/sections covered in this lecture : sections 3-1 through 3-4