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astronomycomets (Comets ** )

Astronomy — Comets


  • There might be as many as 100 billion comets in our Solar System
  • Comets travel in odd orbits, and they are made up of frozen gases and metallic stony grit.
  • A tail of a comet is caused when the comet’s nucleus enters the inner solar system and the Sun’s radiation begins to vaporize the ices, releasing gas and dust.  The presence of the sunlight and solar wind pushes the gases away from the Sun.
  • Comet Swift-Tuttle won’t smash into Earth when it returns in 2126.  Orbital calculations have narrowed its next perihelion to July 11, 2126.  This makes the prospect of an Earth-comet collision very unlikely.
  • In 1996, Comet Hyakutake was discovered.  This article appeared in the Chicago Tribune in March of that year: “Considering how far out in space they are, it is remarkable how easily comets can burn astronomers.  Comet Kohoutek, billed by stargazers as the Comet of the Century, turned out to be an embarrassing dud.  Halley’s, also dubbed the Comet of the Century after its glorious 1910 display, was shy and diminutive in its 1986 return.  And so it is with a delicate balance of restraint and downright giddiness that astronomers are watching the 90,000 mph approach of Comet Hyakutake, already visible in the night sky and growing rapidly in size and brightness.  Over the next week, the potential superstar comet might grow into one of the brightest comets of the century, its candlepower cranked so high that it can be seen even during the day.  Or it might not.  Predicting a comet’s brightness is an exceedingly tricky thing, dependent on a little science, a little guesswork and several variables.  One important variable is already known: Comet Hyakutake will pass extraordinarily close to Earth this weekend.  But another remains a mystery: What exactly is this 10-mile-wide chunk of ice, dust and rock made of, and most important, how dirty is it?  When in the presence of children and laymen, astronomers describe comets as ‘dirty snowballs’. Thousands of these were formed in the deep freeze at the farthest reaches of the solar system near the time of their births.  Some of these city-sized ice chunks occasionally get knocked into a new orbit, which brings them hurtling closer to the Sun, and incidentally, past Earth.  As these cosmic icebergs pass the Sun, they begin to melt, typically losing the outer yard or so of material on each pass.  It is that stuff, which can grow into a hug cloud of dust and gas, that creates the visible comet.  So how big will the Hyakutake show be?  One astronomer predicts that it will be conspicuous and spectacular.  Astronomers expect Hyakutake to hang in the sky in coming weeks like a bright blob, something like the ghost of a full moon.  Unlike meteors, the shooting stars that come from natural space junk falling though the atmosphere, visible comets can hang around for weeks.  By April, as it nears the Sun, the outer yard of the comet will continue to melt and be swept back by solar winds, which might create a marvelous tail.  Or again, it might not.  Astronomers suspect that Comet Hyakutake has made many orbits around the Sun.  Hubble space telescope photos show that as the comet cruises by the Sun and is warmed by solar energy, jets of rapidly expanding gas and dust are erupting with great force through holes in a crust on the comet’s surface.  Comets that have made many trips near the Sun develop a rigid envelope of debris and refrozen ice.  As the comet returns to the  vicinity of the Sun, material under this crust erupts, forming geysers of material.  If this was the first rip around the Sun for Hyakutake there wouldn’t be a crust of rubble formed.  Hyakutake is thought to circle the Sun in an elliptical orbit about every 10,000 years.  If it has been in that orbit since the formation of the Solar System some 4.5 billion years ago, this comet could have make thousands of trips around the Sun.  The comet will pass within 21 million miles of the Sun and be blotted from view by solar glare.  Halley, the best known comet, orbits the Sun and moves within Earth’s view every 76 years.
  • More information on Comet Hyakutake:  “On January 30, 1996, a Japanese photoengraver and amateur ‘comet hunter’, Yuki Hyakutake, scanned his binoculars across a patch of sky over his village and spotted the comet that would bear his name.  It soon became clear that Hyakutake’s comet had the potential to burst out of the arcane world of astronomers.  Of the thousands of comets that have been recorded in history, only 32 have passed closer to Earth than will Hyakutake when it is closest (9.3 million miles).  Even then, though, it will be 40 times farther away from Earth than is the moon.  It will be the closest bright comet since 1556.  Although its proximity teases the possibility of a great sky show, it does not ensure it.  Astronomers have been wrong before.  In 1937, Finsler’s Comet was all the rage, but this newspaper headline summed up what happened: ‘Don’t Look Now, But That Comet Really Is There — Failure of Some To See It Explained”.  Then in 1957:  “Although visible in some places with the naked eye, the Arend-Roland Comet did not live up to the ballyhoo of being the most spectacular in nearly half a century.”  In 1965 came the heralded Comet Ikeya-Seki, though few saw it, and in 1970 it was Comet Bennett that fell short of expectations.  But it is Kohoutek that best shows how a comet’s tail can splash egg on the face of astronomers.  Like the fireball ti never became, Kohoutek roared into the public consciousness in 1973.  Lubos Kohoutek, the 35-year old Czech who discovered the comet, was the guest of honor aboard the Queen Elizabeth II when it set sail with the rich and famous to view the comet from the darkness of the ocean.  But everything turned terribly wrong.  The comet never showed, and the world got nothing more from its stargazing than a collective stiff neck.  When he disembarked form his voyage, Kohoutek meekly said, “I don’t know, I think I saw it,” then complained that he had been horribly seasick.  In the case of Comet Kohoutek, the scientists’ mistake can best be explained by saying that Kohoutek was no dirty snowball, but a very clean one.  It simply didn’t have enough dust on it to put on the show that comets are known for as they melt and cast off debris.  Despite the warnings implicit in Kohoutek’s unpleasant ocean voyage, Hyakutake has accepted an invitation from the Alerd Planetarium to come to Chicago at the height of his comet’s glory – or disgrace.”  This article appeared in the Salt Lake Tribune on Friday, March 22, 1996.

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