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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.
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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