Strange heavenly bodies which sometimes appear with long tails are comets. This comets mostly orbits round the sun, following peculiar paths and changing their shape on the way. The universe is indeed misterous!!
A comet consists of a nucleus, coma and tail, but these parts do not always co-exist. Their existence depends on the comet’s distance from the sun. Appearing as a hazy spot when it is far away from the central body of our planetary system, a comet begins to shine when it is within 300 million kilometers to the sun, causing the dust and gases to vaporize from a misty veil called coma for its resemblance to human hair. With coma, the nucleus constitutes a part usually referred to as head, which is sometime wrapped up in a hydrogen cloud.
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As the comet approaches the sun, solar radiation pressure and solar wind become so strong that they threw all the gases and particles attached to the comet’s head backwards to form one or more trains of light generally known as its tail. The nearer a comet is to the sun, the more powerful the radiation pressure and solar wind are, and the longer the tail. During this time the comet looks like a bloom. 
Measured along with its tail. A comet is very big, through its nucleus usually has a diameter between a few hundred meters and a few dozen kilometer controlling the bulk of comet mass, the nucleus is compose of rocks, dust, ice and frozen gases. The coma change, however, in size, with an average diameter of tens of thousands of kilometers. The biggest coma observed so far dwarfs the sun, covering a space as broad as 1.8 million kilometers.
Of the total of over 1,500 comets identified by the world’s scientists. Hally’s comet is the best known Edmond.
Halley, British astronomer, affirmed by calculations that the comets observed in 1682, 1607 and 1531 were in fact the same one repapering. Named after its discovered, the comet can be seen every 76 years.
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