The Moon
The Moon shines by reflected sunlight. It is the second brightest heavenly body after the Sun and the only Solar System body to be visited by humans. On July 20, 1969, the Apollo 11 mission landed 2 humans on the Moon while a third (Michael Collins) waited in orbit in the command module Columbia. Neil Armstrong (1st) and Edwin "Buzz" Aldrin became the first people to walk on another world after their lunar module, Eagle, landed in the Sea of Tranquillity.
Our satellite, the Moon, is about 1/81 as massive as Earth and has 1/6 the Earth's gravity. If you weigh 54kg on Earth you will weigh only 9kg on the Moon. This is the reason why the Apollo astronauts were able to "walk" on the Moon by leaps and bounds. The Moon has no atmosphere because of its weak gravity; it is not strong enough to hold an atmosphere. There has been a recent discovery of ice at the North pole of the Moon.
When looking at the Moon with the unaided eye, two types of terrain can be noticed. The dark markings on the Moon are called mare, pronounced mar-eh, (maria -plural) meaning "sea" in Latin, and the lighter areas (the highlands) are regions that are heavily covered with craters.
Mare
Long ago, about the time that Galileo first pointed his telescope towards the Moon in 1610, some astronomers thought that the dark areas on the Moon were seas filled with water. We now know that this is not the case, however, the word "sea" or mare has been kept. The seas on the Moon are in fact relatively smooth areas caused by lava flows. This lava covered large regions of the Moon billions of years ago, covering and filling in many craters. The lava does not reflect light well and so appears dark to an observer on Earth.
Craters
The lighter colored regions on the Moon (also called the highlands) are covered with craters. Galileo first discovered these features when he pointed his telescope to the Moon. Craters are circular depressions caused by the impact of meteorites. Some craters on the Moon were caused by volcanoes, however, lunar craters caused by meteorites far outnumber those caused by volcanic activity. Craters on the Moon can vary in size from less than one metre in diameter up to 1,000 km in diameter.
References:
- Asimov, I.Guide to Earth and Space. New York: Random House, 1991.
- R.L. Bishop, ed.Observer's Handbook 1998. Toronto: University of Toronto Press, 1997.
- Enright, Leo. ed.The Beginner's Observing Guide. Toronto: Royal Astronomical society of Canada, 1996.
- Illingworth, V.The Facts on File Dictionary of Astronomy. New York: Facts on File Publications, 1985.
N.A.S.A. Photo Gallery of the moon
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