In the Middle Ages the emergence of comets caused superstitious horror in people. They saw an omen of a devil in comets, considered them premessengers of wars, epidemics and death. Today people know what is comets, and still a lot of things remain not clear and up to the end not studied.
Instruction
1. Scientists found out: comets are a component of the Solar system. "House" of long-period comets is the Oort cloud, korotkoperiodichesky – the Kuiper belt. The body of a comet consists of "tail" and "head" which is a luminescence source. Presumably the head (kernel) consists of strong breeds, ice and gases. A tail - from gas and dust. With approach to the Sun ice and gases of a kernel are warmed, the smallest particles break and all this mix will be transformed to a long loop. This loop carries the name "tail" of a comet. It can be various in a form and the size. Long, short, wide or narrow. It can be extended in a straight line, arc-shaped or fork. Comets which have no tail at all meet.
2. In process of approach of a comet to the Sun the loop grows and the speed of its movement increases. At the same time it flies the head forward. Moving away from the Sun it, on the contrary, flies a tail forward. Speed of the movement falls, the tail becomes less, gradually the comet stops being seen from Earth by a naked eye. Trajectories of the movement of these surprising celestial bodies are similar to orbits of planets. They rotate round its pivot-center, they have "year", a cycle time around the Sun. Some comets appear time in several decades, others once in several dozen millennia. The most known comet – Galley's comet. The period of its address is 75 years. I.e. once in 75 years it is visible from Earth. Astronomers observed it since 239, last time Galley's comet flew by in 1986 and will return only in the 2061st now.
3. It is necessary to consider that comets belong to the category of small space bodies. The asteroids facing them, gravitational fields of planets can influence their orbit. Thereof the probability of collision of comets with planets increases. One of such "accidents" was observed in 1994 in all telescopes of the world. The comet Shumakerov-Levi which broke up to 21 fragments in full operation crashed into Jupiter. This unprecedented case became history of astronomy as the first collision of two large celestial bodies for all history of observations. Similar collision with Earth would incur for itself catastrophic consequences for all live on the planet.