Earth’s Moon is the most famiLiar and aLso the Largest sateLLite in reLation to its pLanet in the entire SoLar System. It is the first body in the SoLar System on which vehicLes from Earth Landed, and the onLy one to be expLored by humans.
|Distance from Earth:||406,711km (furthest, 1912) to 356,375km (closest, 1984), 384,403km (average)|
|Mass:||734,556,000,000 tonnes; a person weighing 65kg on Earth would weigh 10.79kg on the Moon|
|Rotation:||27 days 7 hours 43 minutes 11.5 seconds|
|Surface temperature:||-163’Cto +117’C|
|Largest crater:||South-Pole Aitken (far side) 2,100km diameter, 12km deep (largest in the Solar System)|
ONE AND ONLY
The only human remains on the Moon are those of geologist Eugene Shoemaker who was an expert on planetary collisions. His ashes were carried aboard NASA’s Lunar Prospector spacecraft, which was crashed into a crater on 31 July 1999.
Our Moon’s far side
The far side of our Moon always faces away from Earth, so it was unknown until October 1959, when the Soviet Luna 3 probe sent pictures back to Earth.
Titan is the largest of Saturn’s 34 moons. It is 5,150km in diameter— Larger than the planets’Mercury and Pluto. Dutch astronomer Christiaan Huygens discovered Titan in 1655. We still have no idea what its surface looks like because Titan has a dense atmosphere containing nitrogen, ethane and other gases which shroud its surface — not unlike that of Earth four billion years ago.
Information sent back by the space probe.Voyager 1 during 1980 and recent radio telescope observations suggest that Titan may have ethane “oceans” and “continents” of ice or other solid matter. Cassini, a space probe launched by NASA and the European Space Agency, arrived in Saturn’s orbit on 1 july 2004. On 14 January 2005 it launched the Huygens probe on to the surface of Titan and sent back scientific data.
Triton, discovered in 1846, is the only known large moon in the Solar System with a retrograde orbit. It revolves around its planet (Neptune) in the opposite direction to the planet’s rotation.
British astronomer Edmond Halley (1656—1742) was the first to prove that comets travel in orbits, making it possible to calculate when they wilt next be seen from Earth. He predicted that that the comet he saw in 1682 would return in 1759. It did and was named in his honour. The regular 76-year orbit of Halley’s comet means that we can find historical accounts of its appearances going back more than 2000 years. They were often believed to foretell, important events.
|Date closest to Sun||Observations|
|25 May 240 BC||Seen in China|
|10 October 12 BC||Believed to mark the death of Roman general Agrippa|
|28 June AD 451||Believed to mark the defeat of Attila the Hun|
|20 March 1066||William (later William the Conqueror) believed the comet was a sign of imminent victory over King Harold at the Battle of Hastings. The comet and battle feature in the B’eux Tapestry, made some years Later.|
|9 June 1456||The defeat of the Turkish army by Papal forces was thought to be linked to the comet.|
|15 September 1682||Observed by Edmond Halley, who predicted its return|
|13 March 1759||The comet’s first return, as predicted by Halley, proving his calculations correct|
|16 November 1835||The American author Mark Twain was born this year. He always believed that his fate was linked to that of the comet, and soon after it reappeared in 1910, he died.|
|10 April 1910||There was panic as many believed the world would come to an end.|
|9 February 1986||The Japanese Suisel probe, Soviet Vega 1 and Vega 2 and the European Space Agency’s Giotto space probes passed close to Halley’s comet. Astronomers concluded that the comet is made of dust held together by water and carbon dioxide ice.|
|28 July 2061||Next due to appear|
More than 20 comets return more regularly than Halley. .The most frequent visitor is Encke’s comet, named after the German astronomer Johann Franz Encke (1 791—1865). In 1818 he calculated the 3.3 year period of its orbit. The dosest a comet has ever come to Earth was more than 500 years ago. On 20 February 1491, the so-called comet of 1491 came within 1,406,220km of Earth.
Asteroids are sometimes called minor planets. They are lumps of rock orbiting the Sun, mostly in the asteroid belt between the orbits of Mars and Jupiter.
• The first and largest asteroid, Ceres, is 936km in diameter and was found on New Year’s Day 1801. Since then thousands have been found. Twelve of them are more than 250km wide and 26 are larger than 200km in diameter. As telescopes have improved, more and more small asteroids have been detected. There are probably about 100,000 asteroids larger than 1km in diameter. Some experts think there may be as many as 1.2 million.
• Vesta, the fourth asteroid to be discovered (in 1807), is the only one bright enough to be seen without a telescope.
• Astronomers believe that, on average, one asteroid larger than 0.4km strikes Earth every 50,000 years. Some 65 million years ago a 10km diameter asteroid crashing to Earth may have been responsible for wiping out the dinosaurs. It would have caused a catastrophic explosion, affecting the climate and chemical composition of the atmosphere and destroying the plants and animals on which the dinosaurs fed, As recently as 1991 a small asteroid came within 170,600km of Earth, the closest recorded near miss. On 30 Jan 2052 an asteroid is predicted to pass as close as 119,678km.
• Toutatis (asteroid 4,179) was discovered in 1989. It is named after the Celtic god Toutatis, whose name is used as an oath by the comic strip character Astérix the Gaul. Toutatis measures 4.6 by 2.4 by 1.9km. It passes Earth every four years and is one of the largest space objects to come so cLose to us. On 29 September 2004 Toutatis came within 1,555,818km of Earth. Its next visit will be on 9 November 2008, when it will come within 7,524,773km.