1. Chapter 25 Earth’s Moon

2. 25.1 Origin & Properties of the Moon
4 theories of origin:
1) Earth and moon formed simultaneously
2) Fission: Earth spun so fast that a chunk spun off into orbit
3) Capture: moon formed elsewhere and was caught by Earth’s gravity

3. Origin of the Moon
4) Impact Theory – planet sized object collided with Earth and debris settled into orbit, pulled together and formed the moon
** This is the currently accepted theory!

5. Features of the Moon
Maria: large, dark areas formed from early lava flows
Terrae (highlands): older, lighter areas of the moon with more craters
Impact Craters: formed from meteorites
Weathered and eroded by micrometeorites
No atmosphere!

6. 25.2 The moon’s motions Orbits the Earth in 27 1/3 days
Orbit shape is elliptical
Perigee=nearest to Earth
Apogee=farthest from Earth
We see the same side of the moon because the Moon’s orbit around Earth takes just as long as one rotation on its axis!
Orbital period = rotational period

7. Moon’s Phases

8. Lunar Eclipse Moon enters Earth’s shadow
Can only occur at a full moon phase
Umbra=total shadow
Penumbra=partial shadow
Moon appears orange

9. Solar Eclipse Occurs when moon comes between the sun and Earth
Occurs only at the new moon phase
Total time = 7.5 min
Moon is dark, but sun’s corona is visible around the moon making a gold ring