Why do comets get smaller over time?
Down the ages, comets have been objects of fear. Unlike the planets and the stars, which kept an orderly and reliable place in the night skies, comets were streaks of light that came suddenly and in a few weeks disappeared.
Their ghostly appearance a fuzzy ball with a luminous tail resembled, some said, the head of a demented woman, shrieking a warning from above. The word comet comes in fact from the Greek kome, meaning ‘hair’. Without doubt, comets warned of bad news, some catastrophe in waiting. Inevitably, disaster came. Down the ages, prophets and soothsayers have always found something to support their predictions.
For many centuries, astronomers have tried to unravel the mystery of the vanishing comet. Some argued that once a comet had gone from sight it had gone for good. In 1705, Edmond Halley suggested that a comet he had seen in the sky in 1682 had appeared before. Studying the records, he found that comets were seen in 1456, 1531 and 1607. He argued that this was the same comet, coming back about every seventy six years. He predicted that the comet, which was subsequently named in his honour, would be seen again in 1758. On Christmas night, 1758, a German amateur astronomer spotted the comet, sixteen years after Halley’s death.
Astronomers explain that comets take an elliptical orbit round the Sun. The paths of some are comparatively short. Biela’s Comet, now extinct, was seen every six and three quarter years; others do not return for many centuries.
Comets are massive rocky balls bound together by frozen gases and ice. Each time they approach the Sun some of the gases are warmed and freed, and ice boils away. Sometimes, great chunks of rock fly off. In 1846, Biela’s Comet broke in two. The twin halves did a lap of honour in 1852, before bursting into fragments. For a time, the fragments put on their own fireworks show, peppering the Earth with meteors every November until finally, by the 1980s, the last remnants of Biela were no longer to be seen.
Halley’s Comet came back again in 1986, but the millions who saw it were generally disappointed, a sign perhaps that it, too, is growing smaller and may one day vanish from sight.
Their ghostly appearance a fuzzy ball with a luminous tail resembled, some said, the head of a demented woman, shrieking a warning from above. The word comet comes in fact from the Greek kome, meaning ‘hair’. Without doubt, comets warned of bad news, some catastrophe in waiting. Inevitably, disaster came. Down the ages, prophets and soothsayers have always found something to support their predictions.
For many centuries, astronomers have tried to unravel the mystery of the vanishing comet. Some argued that once a comet had gone from sight it had gone for good. In 1705, Edmond Halley suggested that a comet he had seen in the sky in 1682 had appeared before. Studying the records, he found that comets were seen in 1456, 1531 and 1607. He argued that this was the same comet, coming back about every seventy six years. He predicted that the comet, which was subsequently named in his honour, would be seen again in 1758. On Christmas night, 1758, a German amateur astronomer spotted the comet, sixteen years after Halley’s death.
Astronomers explain that comets take an elliptical orbit round the Sun. The paths of some are comparatively short. Biela’s Comet, now extinct, was seen every six and three quarter years; others do not return for many centuries.
Comets are massive rocky balls bound together by frozen gases and ice. Each time they approach the Sun some of the gases are warmed and freed, and ice boils away. Sometimes, great chunks of rock fly off. In 1846, Biela’s Comet broke in two. The twin halves did a lap of honour in 1852, before bursting into fragments. For a time, the fragments put on their own fireworks show, peppering the Earth with meteors every November until finally, by the 1980s, the last remnants of Biela were no longer to be seen.
Halley’s Comet came back again in 1986, but the millions who saw it were generally disappointed, a sign perhaps that it, too, is growing smaller and may one day vanish from sight.
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