<p>The Moon - Notes What is the Moon? •A natural satellite of a planet •One of more than 96 moons in our Solar System •The only moon of the planet Earth</p><p>Where is the moon? •About 384,000 km (240,000 miles) from Earth •3,468 km (2,155 miles) in diameter (about ¼ the size of Earth)</p><p>Theories of how the moon formed. •“Born” 4-5 billion years ago •Formed from impact of Mars-sized “planetesimal” on Earth •Debris from both objects melted together to form the Moon</p><p>Structure and composition of the moon •Crust - average thickness of about 70 kilometers (O, Si, Mg, Ca, Fe, Al) •Mantle- iron rich silicate minerals •Core - radius is between 300 and 425 kilometers (Fe, Ni, S)</p><p>Environment on the moon •No atmosphere •No liquid water •Extreme temperatures –Daytime = 130C (265°F) –Nighttime = -190C (-310 F) 1/6 Earth’s gravity</p><p>Lunar Features Highlands •Mountains up to 7500 m (25,000 ft) tall •Rilles (trenchlike valleys)</p><p>Craters •Up to 2500 km (1,553 miles) across •Most formed by meteorite impact on the Moon •Some formed by volcanic action inside the Moon •Rays form around impact craters </p><p>Maria (plural of Mare) •Originally thought to be “seas” by early astronomers •Darkest parts of lunar landscape The Moon - Notes •Filled by lava after crash of huge meteorites on lunar surface 3-4 billion years ago Mostly basalt rock</p><p>Movement of the moon •Revolution – Moon orbits the Earth every 27 1/3 days (sidereal month) •Synodic month, from new moon to new moon 29 ½ days •The moon rises in the east and sets in the west •The moon rises and sets 50 minutes later each day •Rotation – Moon turns on its axis every 27 days •Same side of Moon always faces Earth Terminator – boundary between the light part and the dark part of the moon’s disc limb – edge of the visible surface of the moon as viewed from Earth</p><p>Far side of the moon •First seen by Luna 3 Russian space probe in 1959 •Surface features different from near side –More craters –Very few maria –Thicker crust</p><p>Near side of the moon - Many well studied features including the crater Tycho and the Sea of Tranquility (Where the first moon landing was planned) - Thinner crust - More maria than far side</p><p>Orbit of the moon vs. orbit of the Earth - “Wobble” to the moons orbit compared to the Earth’s orbit. - The moon is not always at the same angle to Earth when it is between the Earth and the Sun - This is why eclipses do not happen every month</p><p>What is a lunar eclipse? •Moon moves into Earth’s shadow – this shadow darkens the Moon –Umbra –Penumbra •About 2-3 per year •Last up to 4 hours</p><p>What is a solar eclipse? •Moon moves between Earth and Sun The Moon - Notes •Moon casts a shadow on part of the Earth •Total eclipses rare – only once every 360 years from one location!</p>