There was a time when people considered comets’ appearance as signs of great natural disasters, epidemics, great war, or death.
Humans have a better idea today about comets, although many questions about the stars that even scientists cannot adequately answer. When the comet appears, it is only seen as a bright dot, although it may be several thousand miles in diameter. This bright spot is the head of the comet (nucleus). Scientists believe that the “head” is not necessarily the most solid mass of rock, but can be the solid, sticking matter, hive-like hole and mixed with gas. Where that mass of matter comes from is still a secret.
Comets, when far from the sun, have no tails. But as it gets closer to the sun, a force called solar radiation pressure is applied to the comet’s head and forms a tail. When a comet approaches the sun, its tail is directed backward, but when it “comes out” from the sun, it turns back, meaning that the comet’s tail is always facing the sun. The tail consisted of very light gases and fine particles from the comet’s head that was repelled by solar radiation pressure. Surrounding the comet’s head is the third element of the comet called “coma” or “hair.” It’s a matter cloud, sometimes up to 150,000 miles in diameter, sometimes more.
Comet tails vary in shape and size; and Some are short and ruffled, Some are long and thin. Usually, this tail is 5 million miles long. There are comets with tails up to 100 million miles long. But a comet has no tail.
As the comet’s tail is longer, the comet accelerates, just because the closer it is to the sun, the more gravitational pull – thereby accelerating – and the tail is “blown” out harder. Why does the comet’s tail turn back towards the sun when out of the sun’s influence area? This is still only due to the repulsion of radiation pressure that pushes the tiny particles of the comet’s head back out into a new tail. In other words: going into the sun’s influence area, the comet’s head is ahead of the tail, but when out of the sun’s influence area, the tail goes first, at the same time the tail slowly shortens, the comet’s speed decreases, gradually until lost form.
The comet is out of our site for many years. But most comets return after a while. The comet orbits the sun, but the orbits are so large that it takes a long time to go that orbit. A comet Halley, for example, takes 75 years to make a full turn, meaning that it will take 75 years to see a comet again.
Astronomers have recorded nearly a thousand comets, but it will take a few hundred thousand years to meet all the faces again.