The appearance of a comet has long been considered an important sign. The comet does not fly instantly, it remains visible on the arch for a long time, crossing it with its tail.
The word "comet" is of Greek origin, the Greeks called this beautiful phenomenon "hairy star." Probably due to the tail of the comet. Almost all of them have a tail, larger or smaller, which appears during the flight of this celestial body near the Sun. But what is a comet, and where does its tail come from?
Features of comets
A comet is a celestial body that moves in its own orbit - a strict periodicity of such phenomena is associated with this. The orbits of comets have a very elongated elliptical shape. They are not only in the solar system, they revolve around other stars too. They do not have strict geometric shapes, they can be a block of ice, a kind of cosmic iceberg that rushes through the expanses of the universe. The composition, as a rule, frozen gases, solid particles. At low temperatures in space, the gas becomes a solid, it is frozen in the comet's nucleus and remains so for hundreds, thousands, millions of years.
The observed form of a celestial body strongly depends on how far from its star it is.
When it is far away, it has similarities with the iceberg itself. It can be shrouded in fog, or resemble a small asteroid. But as soon as the comet begins its approach to the luminary, a completely different process begins. It heats up and the evaporation process begins. First, numerous pores are activated on its surface, through which gases thawed from heat begin to escape. The pores are becoming wider, real geysers are breaking out of them, the comet comes to life.
And then the whole nucleus begins to emit streams of gases that form the comet's tail. Sometimes it just becomes huge. Then, when this celestial body again moves farther away from the luminary, receives less light energy, the tail contracts, the emission of gases gradually stops. The comet again turns into a nondescript asteroid, rushing through the cosmic expanses, no different from other similar objects. Until it is again near a heat source. This is her life cycle.
Interesting fact: Each comet has its own period, during which it passes a full circle in its orbit. There are those who return to the luminary every three years or more, but there are others who have been fulfilling their circle for hundreds of years.
Characteristics of comets, their composition
As already mentioned, a comet consists of frozen gas and dust particles. As for its direct structure, it is worth noting that it consists of a nucleus, coma and tail. In any case, the comet remains cold, even under sunlight.And the glow of her tail is nothing more than ionized gases, as well as the reflection of the rays of the sun. The most massive, basic constituent component is precisely the core, in which all the gases forming the coma and tail can be in a dormant state for years. The core is always present, a coma or mantle - also almost always. But the tail of the comet is a variable concept that appears from time to time.
It is difficult for astronomers to study the nucleus of a comet - it is shrouded in a gas-dust mantle almost constantly, this makes it difficult to inspect even through the best telescope. Someone believes that it is extremely solid, like an iceberg. Other scientists say that this is a porous structure like a sponge that breaks even in the hands. There is no consensus, but there is an assumption that comets are both such and such. After all, nature is diverse.
The nucleus of the comet is the heaviest, but also the most inconspicuous. In those moments when this celestial body "spreads its tail", it is not visible at all. But at precisely such a moment, the comet becomes visible, it can be admired, sometimes with the naked eye. The tail is a gas and dust cloud that travels away from the Sun, as it is blown away by the solar wind. It will not be possible to trace the trajectory of the celestial body along it; it does not extend in this direction. But the tail has a bright glow, which can be seen over great distances, because the comet is used to identifying precisely by it.
Difference of Asteroid Comets
Externally, a comet can be confused with an asteroid, but there are significant differences between these celestial bodies.An asteroid is an extremely solid object, it is made of stone, not of ice. And as a rule, it is larger than a comet. He may even have his own companions. The asteroid’s orbit is more rounded, it never has a tail, because it has nothing to vaporize. A comet is a much rarer phenomenon, millions of asteroids are known, and comets a few more than three thousand. Despite the fact that it is still very far from exploring the entire cosmos, it turns out that a comet is a rare phenomenon, not a frequent visitor.
Thus, a comet is a small-sized celestial body, which is formed mainly from a gas-dust mixture. Approaching the star, it thaws, gas fountains forming the tail burst from under its bark. Leaving the illuminated territory, the comet again “hibernates”. Due to the abundant evaporation of the comet, they are not eternal; over time, they completely exhaust themselves.
