The comets are shapeless blocks only a few kilometers in size, consisting of ice mixed with dust particles. Therefore, sometimes they are simply called " lumps of dirty snow." Comets move in very elongated orbits, being mostly far from the Sun, where they remain invisible; LRI their approach to the Sun ice under the influence of solar heat begins to melt, evaporating and evaporating into interplanetary space together with other gases. As a result, many comets passing near the Sun, take a very unusual form.
Never miss an opportunity to observe a bright comet. During the year in a small Amateur telescope you can see only a few of them. Most comets, which periodically appear in the vicinity of the Sun, are quite weak objects. The exception is Halley's comet, which, with each return to the Sun (76 years later), appears to us as a very bright and impressive object. In fact, the brightest and most spectacular-looking comets appear in the sky unexpectedly; many of them, perhaps for the first time, are approaching the Sun. Those few weeks, during which time a comet goes around the Sun quickly, and then disappearing forever or perhaps for many millennia in the cosmic expanses, is the hottest time for astronomers komedchikov. In rare cases, especially if a comet approaches too close to the Sun, it can collapse into parts that are later observed as separate bodies.
Comets
The structure of the comet. The gas tail is always directed away from the Sun, the dust tail remains with the comet in orbit.
Comets look different. All observed misty gas shell-coma, which together with the nucleus forms the head of the comet. Even if the comet is in close proximity to the Sun, its head seems to be no more than a foggy spot. The most remarkable detail of most comets is the tail. It is most striking when the comet is in the vicinity of the perihelion of its orbit. Here, the heat flow from the Sun is particularly significant, under the influence of which gases and dust escape from the comet into space. Some comets have two tails: one is curved, consisting of dust particles; the other is straight, gas, stretched in the direction exactly opposite to the direction of the Sun. A number of comets had several (dusty) tails. The length of comet's tails can reach tens and hundreds of millions of kilometers; comets were observed, the tails of which stretched almost to half the sky. It is assumed that the dust lost by comets, falling into interplanetary space, gives rise to meteor bodies, which later, colliding at high speed with the earth's atmosphere, are found in the form of meteors. Dust from comet tails also join the interplanetary dust cloud that is scattering the sun's rays, gives rise to the phenomenon called the zodiacal light.
The nucleus of a comet is sometimes visible inside a coma in the form of a bright star-shaped object in which it is not possible to distinguish any details even in the largest telescopes. Sometimes the nucleus can be confused with different structural formations in a coma-type shell or ejections of matter from the nucleus of a comet.
The observation of comets
Any tools can be used to observe comets. Experience has shown that giant comet tails can be detected by naked eye observation, through binoculars and telescopes with a wide field of view. But to see the complex structure of a comet near its nucleus, telescopes with large apertures and large magnification are needed. Sketches of comets can be done when observing in any tools, their technique is the same as when sketching planets. Along with the sketches is to try to photograph the comet. Photos help not only to determine the exact position of the head of the comet, but also to get an image of its tail, as well as to see subtle details that due to their low brightness can not be seen in other ways. For the observation of comets requires light-aperture lenses with a wide field of view, for photographing the fine details of the coma is better to use telescopes or long-focus cameras. When photographing comets, the telescope (or camera) must be equipped with a guide system that would monitor the comet in view of its own motion among the stars; in this case, the images of stars in the pictures will be in the form of dashes. When using short-focus lenses, you can guide directly through the stars.
Many experienced Amateur astronomers attempt to detect comets. Such observations require a great deal of patience, a good knowledge of the sky, especially the location on the sky of clusters of stars and galaxies, sometimes very similar in appearance to the comet. Such observations use large binoculars with a wide field of view or short-focus telescopes; comets are usually searched in the vicinity of the Sun, where they can get, while remaining invisible when moving in an elongated orbit.