What Do We Know About A Comet?
The appearance of a comet was considered very inauspicious. People trembled with fear. The comets were believed to be evil omens that for told wars, calamities and death. Now we have a reasonably good idea about the comets. All the answers about them still we don’t have. The first appearance of a comet is marked by a tiny point of light. In actual it may be thousands of kilometers in diameter. The point of light is the nucleus or “The head” of the comet. Scientists believe that a comet is made of a great swarm of a bit of solid matter, combined with gases. The origin of this matter is still a shrouded mystery.
The approach of a comet to the Sun is marked with the usual appearance of a tail behind it. The tail consists of fine particles of matter along with very thin gases. The fine particles are shot off from the nucleus of the comet when it comes under Sun’s influence. The nucleus of the comet is surrounded by “The coma” the third portion of the comet. It is a glowing cloud of matter and assumes a diameter of even 240,000 kilometers, or even more.
The tails of the comet are very different in size and shape; some are short and stubby, others are long and slender. These a usually 8,000,000 kilometers in length and may sometimes even be 160,000,000 kilometers in length. There are some comets with no tail at all.
The growth of the tail indicates a gain in speed and is a result of the comet nearing the Sun, moving with the head leading. A strange thing happens, when the comet goes away from the Sun its tail leads and the head follows. This is due to the fact that the pressure of light from the Sun drives off the very small particles from the comet’s head to form its tail, always in a direction away from the Sun.
When the comet goes away from the Sun its tail must lead. During this journey, its speed slows down and then disappears from sight. These may remain out of sight for years but most of them reappear eventually. These make trip after trip around the Sun but take a long time to complete a single revolution. Halley’s comet takes about 75 years to complete its trip around the Sun. the astronomers have listed about 1,000 comets but there are many more in our solar system which remains unseen.
