On November 8th 1656, Edmund Halley was born. Halley is perhaps most famous for a comet named after him - Halley's Comet. Here are ten facts about Halley's Comet.

FACT ONE Edmund Halley observed a comet that would later be named after him in 1682. He realised that its characteristics were similar to what were believed to be two other comets, one that was observed in 1531 and one that was observed in 1607. Noticing that length of time between each appearance was the same (between 75 and 76 years), he concluded that the three objects were actually the same and predicted that it would appear again in 1758. He was right, and Halley's Comet was visible again from December 25th 1758.

FACT TWO
Halley's Comet is classed as a short period comet, a classification given to any comet that takes less than 200 years to orbit the Sun. It is believed that it was once a long period comet, but at some point the gravity of one of the Gas Giants (Jupiter, Saturn, Uranus or Neptune) attracted the comet. It didn't collide with any of these planets, but instead was flung into the inner Solar System towards the Sun. After orbiting the Sun, it is flung back outwards before being drawn back. This is kind of like a sling shot effect.

FACT THREE
At its closest to the Sun, or its perihelion as scientists like to call it, Halley's Comet is most visible. This is because heat from the Sun causes the comet to burn off dust and gases, which light it up. Halley's Comet gets closer to the Sun than Venus does, but slightly further away than Mercury's orbit. At its most distant, it orbits as far away from the Sun as Pluto does.

FACT FOUR
Because Halley was able to predict the reappearance of his comet, scientists and researchers have been able to go through ancient astronomical records to find other observations of the comet. The oldest record of a comet which is likely to be Halley's Comet is from 240 BC by the Chinese in a chronicle called Records of the Grand Historian. 

FACT FIVE
Halley's Comet appeared in the Bayeux Tapestry, an embroidery depicting the events of the Norman invasion of England and the Battle of Hastings in 1066. As the comet seemed to appear from nowhere, people believed it to be an omen. The tapestry shows one of King Harold's attendants telling the King of the appearance of the "comet star" stating that it is a bad omen, possible a sign of God's wrath for King Harold unrightfully claiming the English throne. 

FACT SIX
It has sometimes been speculated that Halley's Comet is the Star of Bethlehem that the Wise Men saw around the time of the birth of Jesus. Records of Halley's Comet appearances suggest it was observed in 12 BC, but a record of another possible comet was made in 5 BC. This second object appeared in the same place for seventy days with no movement recorded, as if hovering over somewhere, quite possibly Bethlehem.

FACT SEVEN
Halley's Comet is darker than coal, and reflects only 4% of the sunlight it receives. It only shines brightly when it is close enough to the Sun for its dust and vapours to be burnt off.

FACT EIGHT
Halley's Comet is shaped like a peanut and is about 15 kilometres (9 miles) long, and 8 kilometres (5 miles) wide and thick.

FACT NINE
American writer Mark Twain was born on November 30th 1835, two weeks after an appearance of Halley's Comet's. In his biography, he stated that he was born with Halley's Comet, and is likely to die with it. Mark Twain died on April 21st 1910 - the day after Halley's Comet reappeared. 

FACT TEN
Of all the appearances of Halley's Comet, the most disappointing was its most recent in 1986. Fortunately, with the assistance of technology, two space probes were able to get a closer view of the comet. The Soviet Union sent Vega 1 and Vega 2 to visit Halley's Comet, and the European Space Agency sent Giotto. They recorded data and sent back images of the comet.

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