Due to the pressure of the solar wind, the tail always points away from the sun, forming a long tail.
As comets enter the solar system, the closer they get to the sun, the higher their temperature will be, and these icy substances will melt and evaporate. After the comet is heated, the internal pressure will gradually increase, and the gas inside will break through the watch case of the comet and be ejected. The cambered gas film will surround the comet's nucleus, and the closer it is to the sun, the brighter and bigger the glow will be. At this time, Huifa will be dragged out of the tail because of the high-speed flight of the comet.
The tail length is between10 million and10.50 million kilometers. The closer to the sun, the longer the tail.
? Common sense about comets: 1 Definition of Comet: Comet refers to a celestial body that moves around the sun when it enters the solar system. Its brightness and shape will change with the distance from the sun, showing a unique cloud-like appearance.
2. Structure of the comet: The comet is divided into three parts: the nucleus, the coma and the tail (some comets have "comet clouds").
(1) comet nucleus:
The nucleus is the most central, basic and main part of a comet. It is usually considered as a solid, consisting of stone, iron, dust, ammonia, methane and ice. The diameter of the comet nucleus is very small, ranging from several kilometers to more than ten kilometers, and the smallest is only a few hundred meters.
When a comet approaches the sun, it will be decomposed into a comet head and a comet tail under the action of solar radiation, which looks like a broom. So comets are commonly known as brooms.
(2) coma:
It is a planetary mist composed of gas and dust around the core. The radius can reach hundreds of thousands of kilometers, and the average density is less than one billionth of the earth's atmospheric density. Through spectrum and radio observation, it is found that the main components of coma gas are neutral molecules and atoms.
(3) Comet tail:
When the comet approaches the star, the comet material sublimates, forming a hazy coma and a tail composed of thin material flow around the ice core.
Comet tail began to appear when it approached the sun about 300 million kilometers, and gradually changed from small to large and long.
The length and width of the tail are quite different:
The length of the tail ranges from100000 to1500000 km, and some of them are surprisingly long and can span half the sky. For example, the tail of comet 1842 I is 320 million kilometers long and can extend from the sun to the orbit of Mars. The width of the tail is between 6000 and 8000 kilometers, with the widest reaching 24 million kilometers and the narrowest only 2000 kilometers.
According to the shape of the tail and the repulsion from the sun, the tail can be divided into two categories:
One is the "ionic tail", which consists of ionic gases, such as carbon monoxide, hydrogen, carbon dioxide, carbon, hydrogen groups and other ionized molecules. This kind of tail is straight, thin and long, so it is also called "gas tail" or I-tail.
The other is the "dust tail", which consists of dust and yellow, and is formed by repelling dust under the radiation pressure of solar photons.
In addition, there is another kind called "abnormal comet tail", which extends to the solar system in a fan or spike shape.
Generally speaking, a comet has more than two different types of tails.
(4) Comet clouds:
Some comets are surrounded by a huge cloud of hydrogen atoms outside the coma, which is called "comet cloud" or "hydrogen cloud"
The diameter can reach 1 10,000 ~ 1 10,000 km, but some comets have no comet clouds. According to the shape and composition characteristics of the coma head, it can be divided into "coma head", bulbous coma head and anchor coma head.
3. Volume and mass of comets: The mass and density of comets are very small. When it is far away from the sun, it is just an ice block frozen by water, ammonia and methane and a "dirty snowball" mixed with many solid dust particles.
(1) volume: A comet has no fixed volume, but it is very small when it is far from the sun. When approaching the sun, the coma becomes bigger and bigger, the tail becomes longer and the volume becomes very huge. The longest tail can reach more than 200 million kilometers.
(2) Mass: The mass of a comet is very small, and the average density of its nucleus is per cubic centimeter1g. The material in coma and tail is extremely thin, accounting for only 1% ~ 5% of the total mass, or even less.
4. Composition of Comet: Comet material is mainly composed of water, ammonia, methane, cyanide, nitrogen and carbon dioxide, while comet nucleus is composed of water, carbon dioxide (dry ice), ammonia and dust particles condensed into ice.
5. Operation law of comets: (1) The orbits of comets are mostly parabolas or hyperbolas, and a few are ellipses.
Comets with elliptical orbits can return to the sun regularly, and such comets are called periodic comets. A comet with a parabolic or hyperbolic orbit can only approach the sun once in its life, and once it leaves, it will never come back. This is called an aperiodic comet.
(2) Comet tails began to appear when it approached the sun about 300 million kilometers, and gradually changed from small to large and long. When the comet moves away from the sun after passing the perihelion (that is, the comet walks to the nearest point to the sun), the tail of the comet gradually becomes smaller until it disappears.
The tail of a comet is always away from the sun. When the comet approached the sun, it was dragged behind, and when the comet left the sun, it became the leader again. The tail is big, but the material is thin.