Lecture 4
February 7, 2008
A View From the Earth
Key Concepts:
- What causes the phases of the Moon?
- Why do solar and lunar eclipses occur? and why not every month?
Phases of the Moon
Eclipse
- Lunar Eclipse: Sun --> Earth --> Moon ("Shadow of the Earth")
- Solar Eclipse: Sun --> Moon --> Earth ("Shadow of the Moon")
- 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