HALLEY'S COMET

Halley's Comet is arguably the most famous comet. It is a "periodic" comet and returns to Earth's vicinity about every 75 years, making it possible for a human to see it twice in his or her lifetime. The last time it was here was in 1986, and it is projected to return in 2061.

The comet is named after English astronomer Edmond Halley, who examined reports of a comet approaching Earth in 1531, 1607 and 1682. He concluded that these three comets were actually the same comet returning over and over again, and predicted the comet would come again in 1758.

Edmond Halley published "A Synopsis of the Astronomy of Comets" in 1705, cataloging what he had found from searching historical records of 24 comets appearing near Earth between 1337 and 1698. Three of those observations appeared to be very similar in terms of orbit and other parameters, leading Halley to propose that one comet might be visiting Earth again and again.

The comet appeared in 1531, 1607 and 1682. Halley suggested the same comet could return to Earth in 1758. Halley did not live long enough to see its return – he died in 1742 – but his discovery inspired others to name the comet after him.

On each successive journey to the inner solar system, astronomers on Earth turned their telescopes skyward to watch Halley's approach.

Discovery of Halley's Recurrence

FACTS ABOUT HALLEY'S COMET

Halley's Comet is named after the astronomer Edmund Halley (1656 - 1742). Although the comet is named afer him, he didn't actually discover it. Instead, he believed that a comet that he observed in 1682 could be the same comet that had been observed in 1607 and 1531. He believed that comets actually orbit the Sun just like planets and that the comet he had seen would return in about 76 years later if it was to follow the same pattern. It returned in 1758 as he predicted. Although he had died by the time this happened, the comet became known as Halley's Comet.

Halley's Comet takes 75 to 76 years to complete an orbit around the Sun. Comets travel in elliptical orbits, usually going from a great distance away from the Sun (hundreds of millions of miles) to relatively close (just a few million miles) to it. As the get closer Sun, they begin glowing is the Sun burns off its particles. This makes them visible from Earth, and every 75 to 76 years, as Halley's Comet approaches the Sun, it becomes visible in the night sky, looking a bit like a smudged star.

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.

Halley's Comet's most recent appearance was in 1986 when it was photographed close-up by Europe's Giotti space craft and Russia's Vega 1 and Vega 2 space crafts. Its next appearance will be in 2061.

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