P722 CEEFAX 722 Sun 22 Dec 16:49/02 1/8 HALLEY THE COMET - a "hairy star"? Comets are minor mjmbjrs of the solar system - but their appearance can bj spectacular. They were known as "hairy stars" and the word comet comes from the Greek for "long-haired one". Their appearance was often linked with some disaster - Halley's comet in 66AD was blamed for Jerusalem's destruction. It also took the blame for events such as the defeat of Attila the Hun in 451 and the death of Harold in 1066. Of dogs and old ladies 727s5 MoreP722 CEEFAX 722 Sun 22 Dec 16:11/05 2/8 HALLEY THE COMET - periodic orbits Halley's comet has a periodic orbit - it keeps returning to the Sun - and so the correct astronomical reference to it is P/Halley. Its orbit around the Sun is extremely elongated, with one end in the outer regions of the solar system. The path of Halley's comet is affected by the gravitational pull of some of the bigger planets, so its perihelion - the point closest to the Sun - changes slightly each time, and its orbit is an average of 76 years. Ions and the EPA 725s5 MoreP722 CEEFAX 722 Sun 22 Dec 16:41/28 3/8 HALLEY WHY STUDY COMETS? Comets are common phenomena - there are about 1,000 recorded ones - but very little is known in detail about their composition. They are believed to date from when the solar system was formed from a cloud of gases. Comets are therefore considered to bj time capsules containing information about the solar system's early development, and it is not surprising that big efforts are being made bz scientists to study Halley's return. Reception armada 725s3 MoreP722 CEEFAX 722 Sun 22 Dec 16:27/51 4/8 HALLEY THE COMET - snowballs and gas A typical comet is made of three parts. The nucleus of the comet is thought to bj a "dirty snowball" a few kilometres across. As it moves towards the warmth of the sun it emits gas and dust which forms a ball called the coma, which surrounds the nucleus and can bj up to 100 times the size of the earth. The third component is the tail of gas which always points away from the sun and can be 100 million oms in length. ICE and snowballs 725s8-s11 MoreP722 CEEFAX 722 Sun 22 Dec 16:49/14 5/8 HALLEY HISTORY OF HALLEY 240BC First recorded observations bz Chinjsj astronomers. 837AD Closest recorded approach to Earth at 3.72 million miles. 1066 Seen by Harold before battle of Hastings. Incorporated in the Bayeux tapestry. 1301 Seen bz artist Giotto di Bondonj and included in his work The Adoration of the Magi. 1682 Seen - not discovered - by Halley. A certain friendship 726s4 MoreP722 CEEFAX 722 Sun 22 Dec 16:42/17 6/8 HALLEY HISTORY OF HALLEY (continued) 1705 Halley predicts return of the comet in 1758. 1742 Halley dies aged 86. 1758 Comet "rediscovered" bz Johann Palitzsch on December 25. 1835 Second predicted return, observed extensively. 1910 Third predicted return, with the first photographs of the comet taken. Keeping a steady hand 724s2 MoreP722 CEEFAX 722 Sun 22 Dec 16:44/18 7/8 HALLEY ORBIT OF HALLEY Period: 76 years Aphelion: point furthest from Sun 32.29AU = 3003m miles = 4831m km Perihelion: point nearest to Sun - on February 9, 1986 0.587AU = 54.59m miles = 87.82m km Closest approach to earth: April 11, 1986. Distance 0.42AU = 39m miles = 62.83m km. Weekly sky maps 728 MoreP722 CEEFAX 722 Sun 22 Dec 16:46/21 8/8 HALLEY SEEN WITH THE NAKED EYE Two American astronomers have claimed to bj the first to see the comet with the naked eye. They said it was seen without the aid of binoculars or telescopes on November 9 from 7,000ft up the San Gabriel mountains, about 30 miles north-east of Lou Angeles. A British astronomer said hj saw it without binoculars or telescopes the following day from about 9,000ft on Hawaii. Both sightings were made about a week earlier than expected. Comet special index 720 More