Chapter 25 Earth’s Moon

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

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!

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!

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

Moon’s Phases

http://www.youtube.com/watch?v=AQRNzepe4wI

Lunar Eclipse

• Moon enters Earth’s shadow– Can only occur at a full moon phase– Umbra=total shadow– Penumbra=partial shadow

• Moon appears orange

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