The motion of the Moon ANNOUNCEMENTS Assign 1

The motion of the Moon ANNOUNCEMENTS Assign. #1 distributed Friday Sep. 15. Due in your lab section slot, by 5 PM Sep 23. Office hours Mon, Thurs, and Friday this week. See Web page. Lab 1 will be due between Sep. 25 - 28.

The Moon, Our Constant Companion Our goals for learning: • Why do we see phases of the Moon? • What conditions are necessary for an eclipse? • Why were eclipses difficult for ancient peoples to predict ? Note: the Chpt. 2 Moon tutorial on masteringastronomy. com is useful!

Animations Ecliptic Plane Orbit of Moon

Why do we see the same face? Rotation period = orbital period What do you see if you're standing on the Moon looking at Earth?

Animations Causes of lunar phases

Lunar Motion Phases of the Moon’s 29. 5 day cycle • new • Crescent • first quarter (is that synodic or sidereal? ? ? ) Waxing • gibbous • full • gibbous • last quarter • crescent Waning

The lunar phases Notice that the size seems to change. Why? Notice that it 'wobbles' a bit. Why?

The lunar phases Notice that the size seems to change. Why? Moon is not at a constant distance. Notice that it 'wobbles' a bit. Why? Because the orbital speed is not exactly constant Called 'librations'

Why do we see phases? Half the Moon illuminated by Sun and half dark We see some combination of the bright and dark faces

Preliminaries: Local Solar time Interactive applet at mastering astronomy. com

Phases of the Moon. An example: the waxing crescent From the publisher's web site.

Rising/setting times of the Moon Depending on the phase of the Moon it always rises and sets at the same (rough) local solar time. This is due to simple geometry of the illumination by the Sun. See Fig 2. 21 of Cosmic Perspective. NOTE: The times above neglect the Earth's tilt!

Animations Phases of the Moon Rise/set time vs phase Handout given in class

Q: You see a quarter moon rising after drinking in the Pit. What time is it? A) 9 PM B) Midnight C) 3 AM D) 6 AM Bonus : First or Third quarter?

Eclipses : Puzzles for ancient astronomers/astrologers The Earth & Moon cast shadows. When either passes through the other’s shadow, we have an eclipse. Why don’t we have an eclipse every full & new Eclipses Moon? twice a month?

The Moon's orbit is inclined. Moon not necessarily in the ecliptic when it comes `into line' with the Sun

Animations Moon's orbit tilt Eclipse Seasons. . . How rare eclipses

Eclipse Predictions Eclipses recur in the approx. 18 yr, 11 1/3 day saros cycle But even then, eclipse location and type (e. g. , partial, total) may vary. Why?

Lunar Eclipses (way out of scale) From the publisher's web site.

Lunar Eclipse Sequence Is time going L to R or R to L ? ? ?

Lunar eclipse geometry

Solar eclipse geometries Total Partial Annular

Does time go from right to left or left to right here? Time-lapse photo taken in northern Europe

Solar Eclipses Animation