Key Concepts:

1. What causes the phases of the Moon?
2. Why do solar and lunar eclipses occur? and why not every month?

Phases of the Moon

• Moon radiates by reflecting sunlight


• Moon phases depend on relative positions of the Sun, the Moon, and the Earth

• Moon rocks and roll!


• Quiz 4a: It's elementary, Mr. Watson.


• Dark Side of the Moon really means "far side" (as opposed to the "near side").


• What's a blue moon?

Eclipse

• Lunar Eclipse: Sun --> Earth --> Moon ("Shadow of the Earth")
• umbra and penumbra (also see APOD image)


• total, partial, and penumbra lunar eclipse




• Solar Eclipse: Sun --> Moon --> Earth ("Shadow of the Moon")
• total, partial, and annular solar eclipse




• Why eclipse does not happen every month?



• Quiz 4b: How lucky are we?
• Moon's orbit tipped by about 5 degrees with respect to Earth's orbital plane
• Eclipse "season": Moon orbit crosses Earth orbital plane only twice a year
• Moon's diameter only about 1/4 of the Earth diameter
• Moon's distance only about 1/100 of the distance to the Sun





• Eclipse can involve other solar system bodies as well (e.g. Venus)

Reading assignment for next lecture: Units 11 & 12