Before the seventeenth century, comets were considered portents-warning shots fired at asinful Earth from the right hand of an avenging God. However, in the post-Newtonian era, whentheir paths were understood to intersect that of the Earth, they were considered actual agents ofdestruction. Experts have described comets as the carriers of both life-seeds to the early Earthand horrific missiles that will one day snuff out life as we know it. At one time or another,people have blamed comets for war and held responsible for the deaths of men, the birth of goodwine, the London fire of 1666, severely cold weather, etc . . . If one central theme runsthroughout history of comets, it must be the public concern they have commanded.
Comets are ancient objects, formed in the outer reaches of the Solar System from the iceof gases such as methane, water vapor, and ammonia, combined with dust from primitive rockcompounds. Sometimes comets are described as “dirty snowballs” because they are icy lumps,or wandering icebergs. Comets are relatively tiny- just a few miles across on average. Theirnuclei are very different from glowing balls of light, with multimillion-mile-long tails. This isone reason comets occasionally visit the inner Solar System.
Astronomers divide comets into long-period types with orbits of more than 200 years andshort-period types with orbits of less than 200 years (as cited in Branley 1988 p. 43). All cometsbegin their journey as long- period types. Gravitational fields of planets then capture long-period comets. Comets can have orbits at any angle because they can come from any region.
Once comets are captured, they fall into line with the movement of planets, staying close to theecliptic, orbiting the sun in the same direction as the planets. One exception is Halley’s Comet.
It is a short-period comet with an orbital period of about seventy-six years- known as retrogradeorbits (as cited in Branley 1988 p. 44). Retrograde orbits are simply clockwise orbital motion, asseen from the north pole of a planet. Most Solar System orbits are counter clockwise.
Like people, comets group too. When several comets with different periods travel innearly the same orbit, experts say that they are members of a comet group. One well-knowngroup includes the spectacular Sun-grazing comet, Ikeya-Seki, of 1965, and seven others havingperiods of nearly a thousand years. Brian G. Marsden, an American astronomer, has concludedthat a 1965 comet and the even brighter comet of 1882 split from a parent comet, possibly theone of 1106 (as cited in Yeomans 1991 p. 184).
One interesting contribution of the comet is the solar effect. The process starts by acomet approaching the sun. Once the comet approaches the sun, solar heat sublimates, orevaporates, the ices. This causes the comet to brighten enormously. Sometimes this develops abrilliant tail, extending millions of kilometers into space. Even as the comet recedes again, theWhat are these spectacular comet tails composed of? Comet tails are made up of simpleionized molecules, including carbon monoxide and dioxide. By action of solar wind, moleculesare blown away, forming a thin stream of hot gases continuously ejected from the solar corona.
In case you do not know the meaning of a solar corona, it is the outermost atmosphere of theSun. Amazingly, the thin streams of high gases move at a speed of approximately 400kilometers (250 miles) per second (as cited in Yeomans 1991 p. 185). In addition, a cometfrequently also displays smaller, curved tails composed of fine dust particles blown from thecoma by the pressure of solar radiation.
Yet, as a comet recedes from the Sun, the loss of gas and other dust particles decrease inquantity, which contribute to the disappearance of the tail. Some comets with small orbitscontain tails so short that they are practically invisible. However, the tail of at least one comethas indeed exceeded approximately 320 million kilometers (200 million miles) in length (as citedin Yeornans 1991 p. 183). Surprisingly, of some 1400 comets on record, fewer than half the tailswere visible to the naked eye, and fewer than 10 percent were conspicuous (as cited in YeornansInterestingly, amateur astronomer Yuji Hayukutake from Hawaii, discovered CometHayukutake. This discovery was on January 30, 1996 (as cited in rosat-goc-comet) However,mid -march is at its most visible in the northern hemisphere. This surprise comet has turned outto be the closest and most spectacular of the century. This comet was the brightest comet tocome near the earth in more than twenty years. Comet Hayukutake gave astronomers a wealth ofNot only did Comet Hayukutake bring new discovery with images, but it also renewedinterest in observational astronomy when it passed the Earth in early 1996. The comet improvedperceptions of the constellation it transversed. The appearance of Comet Hayukutake in March of1996, inspired the same sense of wonder in those who observed it as the ancients who first sawcomets in the sky. Many ancient astronomers have linked comets to dragons breathing fire intothe atmosphere, and viewers can readily see this while observing these celestial spheres (as cited in Vogt1993 p. 25). Both amateur and professional astronomers relayed heavily on enthusiastic reports of their observations on Comet Hayukutake when it appeared for several days in March of 1996.
The comet provided clear observations of its gas jets, fans and rare disconnection event as itmoved towards the sun. (as cited in rosat-goc-comet).
Did you know Comet Hayukutake, a I O-mile-wide block of space dust and ice, passedwithin 9.3 million miles of Earth on March 25, 1996? (as cited in encarta 1994). Although theHubble telescope provided many excellent pictures of the comet, amateur astronomers haveaided in tracking the comet. For those of us who were too busy to see this spectacular object,NASA’S web page provided a graphic picture of the comet, so we too, could get a glimpse ofthis spectacular sight of Comet Hayukutake.
When astronomers observed Comet Hayukutake on March 27, 1996, they made the firstever extreme ultra violet (EUV) image of a comet (as cited in rosat-goc-comet). Interestingly,this observation of Comet Hayukutake was simultaneous with the X-ray measurements madefrom the US, provided High Resolution Imager, reported in April.
Why are these first ever X-ray/EUV images of a comet so remarkable? These imagesprovided great, and quite unexpected-brightness. Many astronomers discovered large changes inbrightness over a few hours. This very important discovery showed that previous unsuspected”high energy” processes must have been taking place in the comet. High energy was probablydue to the influence of the Sun’s radiation and solar wind.
Astronomers who pointed the German X-ray Roentgen Satellite at Comet Hayukutakewere surprised by a brilliant X-ray emission, especially since no X-ray had ever before beendetected from a comet (as cited in rosat-goc-comet). One theory is that solar X-rays interacting with water molecules in the comet produced the emission. On the other hand, some researchersbelieved that some X-rays were generated through the interaction between the Sun’s solar windand the comet itself. According to astronomer Michael Di Santi and his colleagues, theyidentified methane and ethane in Comet Hayukutake as it passed Earth in March of 1996 (ascited in rosat-goc-comet). Neither compound had ever been confirmed in comets, but themethane surprised many. This compound was not believed to have been part of the materialFor many, this comet was by far the most interesting thing to have witnessed. A mandescribes viewing Comet Hayukutake the night before its closest approach to Earth with anumber of amateur astronomers atop Mount TamalpaisJust north of San Francisco, California.
Many were impressed with Comet Hayukutake. However, the sight was not charming for all.
Comets have been given the title “great” throughout history for being aw-inspiring, for spurringinterest in astronomy and for their high visibility during perigee, the point at which is closestfrom the object to the earth. According to urban citizens. Comet Hayukutake did not producesuch an effect on people since its appearance was obscured by light pollution in the cities.
According to all astronomers, the range of phenomena attributed to comets areextraordinary. Some of it true, much of it nonsense. But all of it adds to their considerablemystique and perhaps explains the universal interest shown in these, the solar systems’ smallestbodies. Comets are currently thought to be the building blocks of the major planets and sourcesfor some of Earth’s water, volatiles, and organic molecules. Commentary impacts on Earth havedeposited some of the biogenic material from which primitive life may have ultimately formed (as cited inYeomans, 1991 p. 228).
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