A comet is one of the celestial bodies in outer space. It consists mainly of ice, frozen gases and particles of dust. On its passage around the sun, it develops a tail of glowing gases and this tail could extend for millions of miles. When it becomes visible, it can stay in view for a few days or a few months. Once it sweeps around the sun, it takes a different path and goes back to wherever it came from. Some comets return on a regular basis, some only rarely and some are only seen one time.
There are three parts to a comet – the nucleus, the head and the tail. The nucleus is the main body of the comet that can range in size from less than a mile to up to 60 miles in diameter. This is the part that contains the frozen materials and dust particles. The head and tail are huge and have very little mass. The head forms when the comet gets nearer to the sun, which then heats the frozen substances and vaporizes them. The gases, containing bits of dust, then fly off in all directions. This is the largest part of the comet and could range from 10,000 miles to over 1,000,000 miles in diameter.
As the gases fly off in the various directions, they come in contact with solar wind. This wind causes a long stream of gases to flow out from the head, creating the tail of the comet. The tail does not follow the comet, but instead it points away from the sun. The tail can be very short, in which case it is curves, or it could be more than 100 million miles long.
The radiation of the sun causes the comet to light up. The radiance is increased by the presence of the dust particles that reflect the sunlight. The head and tail of a comet become larger and brighter as it draws closer to the sun. Comets are affected by the gravitational pull of the sun and the planets. They are visible only when they are close to the sun and then, only at sunrise or sunset.
Comets are one of the celestial bodies that have been known for centuries, even as far back as prehistoric times. For the people of these times, they were seen omens of disaster. The most famous of all comets, Halleys Comet, was depicted in Chinese art as far back as 240 B.C. and it is detailed in the Bayeux Tapestry, commemorating the Norman Conquest of Britain in 1066. This comet appears every 76 years. It was last seen in 1986, so it will not appear again until 2062.