In ancient times, the appearance of a bright comet in the sky plunged people fear. Ignorance of the phenomena of nature made them in the eyes of people harbinger of terrible events such as war and epidemics. The appearance of a comet seems only a rare event, as most of them are visible only in the medium and large telescopes. Known previously added are now numerous comets that were previously unseen due to insufficient funds optical observations. Currently, every year there are several open. The total number of them is estimated at several million or billion.

In ancient times, the appearance of a bright comet in the sky plunged people fear

Most comets can be decomposed into three parts: the core, the surrounding skin and (not always available) tail. Starlike nucleus forms an important component part; although it has a small size but contains a basic weight of the comet.

Under the influence of solar radiation of the gaseous component of the comet partially leaves the nucleus and forms a shell and tail. While the core has a diameter of up to 1000 km presumably, shell diameter can reach tens and hundreds of thousands of kilometers. Tail length is often up to several million kilometers, is only formed when the comet will approach enough to the Sun; it thus strongly repelled by the sun.

On the likely structure of the comet can be obtained from spectroscopic observations. According to these data, the kernel is a cloud of meteorites, ice particles and gas. Shell is a cloud of gas mixed with meteoric dust; tail is the formation of gas, which is likely, the pressure of radiation and corpuscular radiation of the sun swept out of the core and shell.

The orbits of comets are in most cases, highly elongated ellipses. Comets with time of revolution around the Sun is not more than 200 years are called comets short period (Encke comet, Halley). If the time interval between the moments of comets appear longer, they are called comets with a long period. Some comets discovered parabolic or hyperbolic orbits. It is open curves. Such comets are not returned to the starting point and not become visible again. But there are many reasons to believe that the orbits of these comets still elliptical but greatly extended.

The name of each comet usually receives the name of the discoverer or the calculator of its orbit. In addition, each comet is digital or letter designation from which you can learn in what year and what the account this year it was open.

Time comet lives of about a million years. Just over time, the sun evaporates the particles of the gaseous shell and tail. Gradually, it destroys the kernel.