Motion of the Moon Lecture 5

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

lunar phases = different appearances of the Moon What is causing the phase of the Moon? What is causing the phase of the Moon? Common mis-conception = shadow of the Earth Common mis-conception = shadow of the Earth Phase of the Moon

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

Why the Moon goes through phases relationship b/w lunar phases and Moon’s positions in its orbit

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?

Because the Earth shines the un- illuminated side of the Moon  known as Earthshine. Earthshine

Moon’s synchronous rotation

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

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

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.’7 Moon’s angular diameter : 29.’3—34.’1 Different eclipses

Conditions for Eclipses

Total Lunar Eclipse Nine photographs over 3 hours during the total lunar eclipse of Jan 20, Nine photographs over 3 hours during the total lunar eclipse of Jan 20, Lunar eclipses can be seen nearly all across the world (why?) Lunar eclipses can be seen nearly all across the world (why?)

Three types of lunar eclipses

In summary… Important Concepts Moon’s phase and time if its visibilities relative to the Sun Synchronous rotation of the Moon Mechanism of eclipse Important Terms lunar phase sidereal month synodic month Earthshine line of nodes umbra and penumbra Chapter/sections covered in this lecture : sections 3-1 through 3-4