Sometimes a strange star with a tail can be seen in the night sky. But this is far from a star. It's a comet. This phenomenon was observed by people in ancient times. Large tailed stars in ancient times were considered an atmospheric phenomenon. Often, the appearance of a comet was explained as a harbinger of great troubles, wars and misfortunes. The belonging of comets to atmospheric phenomena was denied by Brahe. He noted that the comet from 1577 occupies the same location when observed from different points, which proves its location farther than the Moon.
Halley, the famous astronomer of 1705, was able to explain the movement of comets. He found that comets move in parabolic orbits. He is credited with determining the orbits of 24 comets. In doing so, he determined that the comets of 1531, 1607 and 1682 have fairly similar orbits. This discovery helped him to conclude that this is the same comet, which with a period of 76 years approaches the Earth in a very elongated orbit. This one of the brightest comets was named after him.
At first, comets were discovered purely visually, but over time they began to open from photographs. In our time, a fairly large number of comets are visually revealed. Each new open comet is assigned the name of the person who discovered it, with the addition of the year of discovery and a serial number among the comets discovered in that year. A fairly small number of comets are periodic, that is, they appear regularly within the solar system. Most comets have such an elongated orbit that it is close to parabolas. The orbital period of such comets can be up to many millions of years. These comets are moving away from the Sun at interstellar distances and may never return back.
The orbits of periodic comets are less elongated, therefore, they have completely different characteristics. Of the forty periodic comets observed in the solar system, 35 have orbits that are inclined to the plane of the ecliptic by less than 45 degrees. Alone of all, Halley's comet has an orbit greater than 90s. This suggests that it is moving in the opposite direction. There is the so-called Jupiter family. These comets are short-period, that is, having periods from three to ten years.
There is an assumption that this family was formed as a result of the capture of comets by planets that previously moved in more elongated orbits. But depending on the relative position of the comet and Jupiter, the comet's orbit can both increase and decrease. The orbit of a periodic comet can undergo quite dramatic changes. In one case, a comet passing many times near the earth, perhaps, due to the attraction of giant planets, so change its orbit that as a result it becomes unobservable. In other cases, on the contrary, a comet that has never been observed before, becomes visible, due to a change in its orbit due to its passage near Jupiter or Saturn. But, orbital changes so dramatically are rare. Despite this, the orbits of comets are constantly changing. But, not only this is the reason for the disappearance of comets.
In addition, comets disintegrate rather quickly. An example of this was the comet Biela. It was opened in 1772. After that, it was observed three times, and in 1845, it turned out to be enlarged, and the next year, those observing it, were surprised to see instead of one, two comets very close to each other. When calculating, it was found that the comet split a year ago, but due to the fact that its components were projected one on top of the other, they did not notice this immediately. At the next observation of this comet, one part was noticeably smaller than the other, and a year later no one else observed it. Although, judging by the meteor shower passing strictly along the orbit of the former comet, it is safe to say that it collapsed.
Comet tail
is also quite an interesting object. It is always directed from the Sun. If the comet is at a considerable distance from the Sun, there is no one hundred tail at all. But the closer it gets to the Sun, the larger the tail becomes. Corpuscular streams and light pressure push the comet's tail away from the Sun. If condensations or clouds are noticeable in the tail, then it becomes possible to measure the speed of movement of the substance of which it is composed. There are times when the velocities of matter in the tail of a comet are simply enormous and exceed the gravity of the Sun by a hundred times. Although more often this value does not exceed several times.
For convenience, it is customary to subdivide cometary tails into three types:
- Type I are tails that have a repulsive force of ten to one hundred times the sun's gravity. Such tails are located almost exactly from the Sun;
- Type II - has a repulsive force slightly more than attraction. Such a tail is slightly curved;
- Type III - has a strongly curved tail, which suggests that the Sun's gravity is more repulsive.
It is not possible to establish the exact mass of comets due to the fact that it is too small to somehow influence the motion of the planets. Presumably the upper limit of the comet's mass is 10 (-4) from Earth. In fact, this value can be much less.
It can be concluded that the density of the substance of which the comet is composed is also rather low. The comet's nucleus is surrounded by a very rarefied gas environment. It itself is solid and is approximately one to thirty kilometers. It consists of volatile substances, but in a solid state. When approaching the Sun, ice sublimation occurs, as a result of which a tail visible to us appears.
