Moon
Humans have been observing the Moon since ancient times in hopes of explaining the mysteries of its movements, topography, origin, and composition. Early records of lunar study date back to 2200 b.c., when the Mesopotamians observed lunar eclipses. By 500 b.c. the Chaldeans had developed a system of predicting eclipses, and Aristotle, the Greek philosopher, concluded that the Earth was ball-shaped based on his study of lunar eclipses circa 335 b.c. Other ancient discoveries include the observation by Anaxagoras, a Greek philosopher, that the Moon does not produce its own light but reflects sunlight, and Posidonius's explanation of the Moon's effect on the Earth's ocean tides.
The first attempt at figuring the distance between the Earth and the Moon was carried out by Aristarchus, a Greek astronomer, around 280 b.c., but the mathematical and technological advances of the Renaissance allowed for a more accurate and detailed study of the Moon. In 1609, Galileo Galilei, the Italian astronomer and physicist, made the first scientific observations of the Moon with a telescope. He discovered that the lunar surface is covered with craters and he observed large, dark areas that appeared to be bodies of liquid; hence, he named the dark patches maria, which is Latin for seas. The invention of the telescope also enabled Johann Hevelius (1611-1687), a Polish astronomer credited with being the founder of lunar topography, to chart 250 lunar formations in 1645.
The practice of bestowing the names of philosophers and scientists on lunar formations was started by Riccioli, an Italian astronomer, in 1651. Today, lunar craters still bear the names of Tycho Brahe, Nicholas Copernicus, Johannes Kepler, and Plato, among others.
In 1750 Tobias Mayer, a lunar topographer, discovered that slightly more than half of the Moon is visible from Earth due to the degree to which the moon is tilted on its axis. The Moon wobbles slightly, in the way that a ball suspended on the end of a string might slowly twist back and forth slightly. This phenomenon is called libration.
While Mayer and other early astronomers were able to explain the movements and topography of the Moon, it was not until the Space Age that accurate data on the physical characteristics of the Moon were available. This feat was accomplished by scientists from the United States and the former Soviet Union by sending manned and unmanned spacecraft to the Moon. The Soviets launched the first unmanned spacecraft to reach the Moon, the Luna 2, in 1959. Later that year, the Luna 3 took photographs of the far side of the Moon, allowing man to see that sight for the first time. Increasingly sophisticated missions followed, and in 1969 the United States' Apollo 11 astronauts became the first men to walk on the Moon. They collected rock and soil samples that were brought back to Earth to be analyzed.
The layer of soil on the Moon ranges from five to twenty feet deep and consists of rock fragments, pulverized rock, and tiny pieces of glass, which comprises approximately half of the soil content. Lunar rocks consist of two types: basalt, which is hardened lava, and breccia, which consists of soil and rock fragments that have been melted together. The minerals contained in the rocks include aluminum, calcium, iron, magnesium, and titanium. No new elements were found on the Moon, although certain elements that do not occur naturally on Earth were found. Using the rock and soil samples, scientists determined that the Moon is 4.6 billion years old--the same age as the Earth.
Modern technology has also allowed us to improve upon the discoveries of early scientists. Man has been trying since ancient times, with varying degrees of accuracy, to measure the distance between the Earth and the Moon; in 1970 the Lunokhod 1, a Soviet remote-controlled lunar vehicle, obtained a measurement that is no more than 30 centimeters off the mark. Also, it is now known that the maria are not bodies of liquid but basins filled with volcanic basalts. Evidence indicates the maria were filled by lava flowing up from the interior of the Moon. The general consensus in the scientific community is that lunar craters, which range in size from microscopic to 300 kilometers, were formed by meteorites that bombarded the Moon billions of years ago. This theory is supported by the fact that the Moon has virtually no atmosphere; it is not enveloped by layers of protective gases that can lessen or eliminate the impact of meteorites, and the absence of weathering processes prevents craters from being eroded and filled in over time as they are on Earth.
Since the Moon lacks an atmosphere, it is subject to extreme temperatures, as well as extreme fluctuations in temperature. The Lunokhod 1 recorded the Moon's temperature dropping from 138° C to-100° C during an eclipse. Another result of the lack of atmosphere is that there is no weather on the Moon--no clouds, wind, air, or rain.
Modern science has yet to explain the origin of the Moon. There is evidence to support the theory that the Moon was spun off from the Earth as Earth was forming and rapidly rotating in a molten state. However, the Earth and Moon may have formed simultaneously and orbited each other, or the Moon may have been blasted out of the molten Earth by a large impact during our planet's formative period.
There was renewed interest in exploration of the Moon in the 1990s. On January 25, 1994, the Clementine mission was launched, and on February 19 of that year the unmanned spacecraft settled into lunar orbit. Its primary mission was a detailed topographic survey of the entire Moon. After leaving lunar orbit on Mary 5, 1994, Clementine was scheduled to fly by the near-Earth asteroid Geographos, but a malfunction prevented this.
Four years later, on January 6, 1998, the Lunar Prospector spacecraft was launched. Lunar Prospector settled into a very tight lunar orbit, only 63 km (about 40 miles) above the lunar surface. It was armed with further mapping instruments, as well as experiments to examine the lunar magnetic field, gravitational field, and the nature of the lunar core. A stunning discovery made by the Lunar Prospector was the presence of large amounts of water ice in shadowed parts of craters near the lunar poles. Here, in the coldest reaches of our satellite, was a huge store of water, covering some 10,000 square kilometers in the south polar region, and perhaps twice that in the north polar region.
Clearly these missions of the 1990s were intended as scouting reports for conditions on the Moon, as precursors to further manned missions. The Moon is the obvious first place for a space outpost or colony, and the existence of water is a huge boost for the logistical problems of supporting humans for long periods of time in such an otherwise harsh environment. Two decades after the Apollo missions left their brief marks on the Moon, the stage is being set for more ambitious, longer-term occupation of the Earth's only natural satellite.
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