Why do comets have tails What is the tail of a comet

How exactly is a comet tail formed? In the 17th century, Newton put forward the mechanical theory, postulating that the shape of the comet tail is explained by the structure of matter, and that the comet tail is formed due to the repulsion of light, which causes the comet head to flow out of matter. Since then, scientists such as Olbers, Bessel, Pape, and Winnecke have studied the problem of solar repulsion and comets.

It was not until further development of theoretical physics that it was discovered that one of the effects of sunlight on comets was solar radiation pressure. It turns out that solar radiation (including visible light and other electromagnetic waves) shines on an object, and its direction of incidence creates a pressure; This pressure increases according to the intensity of the light and is proportional to the area of the object perpendicular to the light. This pressure is insignificant for an average-sized object.

A completely reflective object placed in sunlight outside the atmosphere has an area of 1 square meter with a radiation pressure of grams; For objects that completely absorb light, this figure is halved, which shows the weakness of this force. But for extremely small objects such as dust particles, gas molecules, etc., the radiation pressure is particularly obvious, and it is stronger than the gravitational pull of the sun, another force of action. The gravitational pull of the sun is the opposite of the repulsive force of sunlight, but both forces are inversely proportional to the square of the distance.

For objects in general, the gravitational pull of the sun prevails. But for very fine particles, why does the sun's repulsion outweigh the sun's attraction? To illustrate this, we can use the analogy of an object falling:

The greater the surface area, the greater the resistance, and the slower the fall. The effect of radiation pressure on tiny particles is similar, because the smaller the plasmid, the greater the surface area for its weight. For example, suppose a square object has a volume of 1 cubic centimeter, a mass of 1 gram, and a surface area of 6 square centimeters. If you cut it and divide it into two identical cuboids, then the mass of each is grams, and the surface area of each cuboid is 4 square centimeters, and the sum of the surface area of the two cuboids is 8 square centimeters, which is larger than the original relative amount of the overall surface area, so the relative mass of the surface area of the tiny particles is very large, and the accompanying repulsion force is extremely significant

As long as the diameter of the particle is equal to 1 micron, the repulsive force of the sun and the gravitational force are equalized. If the particle is smaller, the repulsion force of the sun is greater than the gravitational force. Therefore, the solar radiation pressure becomes a force to repel the comet. Since the discovery of the repulsive effect of solar radiation on comets, many scientists have used the solar radiation pressure to explain the tail of the comet, but unfortunately the results are not satisfactory, and they cannot explain why the acceleration of the tail is so high.

The problem was caused by the appearance of the comet Morechouse's Comet in 1980, which ejected material at a speed of 30 kilometers per second, which cannot be explained by solar radiation pressure. It wasn't until the discovery of the solar wind that a reasonable answer was found.

The heat melts the frozen material and fires it away from the sun, making it look like a tail.

In addition, comets do not have tails when they are far away from hot stars, because they are frozen ......

If you throw a fireball down from the roof, you see if there's a tail, and that's because the object is moving too fast.

The comet dome is quietly divided into three parts: "comet head", "comet hair" and "comet tail". The core of the comet's head is the core of the comet's devastated comet, which is made of icy matter because it was born in a cold place. When the comet approaches the Sun, the material of the comet nucleus sublimates and forms a hazy mass around the comet nucleus in the head, called a comet.

The comet's volatile matter is dragged into a tail of a thin stream of matter, shaped like a broom, which is called a comet tail.

The tail of a comet is solar radiation and solar wind.

For most of the time of its orbit, the comet does not have a comet tail, only when it reaches a distance of about 2 astronomical units (about 300 million kilometers) from the sun, under the action of the solar wind and the pressure from the sun, the gas and particulate dust thrown from the comet head extend outward to form the comet tail.

Comet tails come in a variety of shapes and can be summarized into three types, namely I-type, type, and type. Type I tail is mainly formed by a gas composed of charged particle ions, and the tail is relatively straight and thin, with a slight bluish tinge.

Type and type comet tail are composed of dust, pale yellow, wider than type I, and more curved, the less curved is called the type comet tail, and the more curved degree is the type comet tail.

Because there are both gas and dust in the comet's tail, it is not uncommon for a comet to have both a gas comet tail and a dust comet tail when it is closer to the sun and more active. This was the case in February 1986 when Halley's Comet passed perihelion in its orbit, when its morphology developed more colorfully.

Sometimes, the tail of the comet of a handful of comets' gas and dust develops into a continuous piece, like a large broom hanging upside down in the sky. A notable example of this is the Comet West, discovered in 1975 and past perihelion in 1976.

The two large comets with the most tails were the two large comets that appeared in 1825 and 1744, with the former being observed in Australia with five comets and the latter being seen by a Swiss astronomer with six tails rising from the horizon. On the third comet of 1903, photographed by the Greenwich Observatory in the United Kingdom, nine comet tails can be clearly distinguished.

Although there are doubts about the reliability of the nine-tailed comet message, one thing is certain, that is, comets often have more than two comet tails, and faint comet tails that are not discernible to the naked eye can often be found on the comet**.

This is due to the fact that when close to the Sun, comets release gas and dust under the action of the Sun.

As the comet gets closer to the Sun, the solar radiation is strong enough to sublimate water vapor, carbon dioxide, methane, ammonia and carbon monoxide, which are the five most important gaseous substances that the comet sublimates. Among them, the friendly carbon in the oxygen is the most easily ionized to form carbon monoxide ions. The ion comet tail is mainly carbon monoxide ions, which emits blue wavelengths of light, so the wild friend is blue.

Dust is released from the comet with the sublimated material, and when the dust reflects sunlight, it creates a very weak force called "radiation pressure" that pushes the tiny dust away from the sun. This creates a dust comet tail. And because the dust comet tail can reflect all wavelengths of light, it is brighter than the ion comet tail.

Comet tails begin to appear about 300 million kilometers (2 AU) from the Sun when the comet is close to the Sun, and gradually change from small to large to long. When the comet passes perihelion (i.e., the comet walks to the closest point to the Sun) and moves away from the Sun, the tail of the comet gradually decreases until it is gone.

The direction of the comet's tail is generally extended away from the Sun, and when the comet approaches the Sun, the comet's tail drags behind, and when the comet moves away from the Sun, the comet's tail becomes the leader. Comet tails are large in size but thin in substance.

The length and width of the comet's tail are also very different, generally the comet's tail is between 10 million and 100 million kilometers long, and some are surprisingly long, and can cross half the sky, such as the comet tail of 1842 is up to 100 million kilometers, which can stretch from the sun to the orbit of Mars. Generally, the width of the comet's tail is between 6,000 and 8,000 kilometers, with a maximum width of 24 million kilometers and a narrowest of only 2,000 kilometers.

Because the comet is a cloud-like celestial body, the solar wind and gravitational pull will cause the gas and dust on the comet to extend into a shiny tail during its movement, so it looks like it is dragging a tail. Comets are shaped like brooms and are popularly known as broom stars. More than 1,700 comets have been found orbiting the Sun, and the famous Halley's Comet orbits the Sun for 76 years.

Effect of comet tail formation:

1.The initial momentum obtained when the gas and associated dust evaporate from the nucleus of the comet.

2.The radiant pressure of sunlight pushes dust away from the sun.

3.The solar wind blows charged particles and dust away from the sun.

4.Gravitational attraction towards the sun.

The orbit of a comet is mostly parabolic or hyperbola, a few are elliptical, it does not have a fixed volume, and when it is far from the sun, the volume is small; As it approaches the Sun, the comet grows larger and larger, and its tail becomes longer and larger, reaching a maximum length of more than 200 million kilometers.

The comet mass is very small, the comet material is mainly composed of water, ammonia, methane, cyanide, nitrogen, carbon dioxide, etc., while the comet nucleus is composed of a mixture of water, carbon dioxide (dry ice), ammonia, and dust particles that have condensed into ice. The average density of the nucleus of the comet is 1 gram per cubic centimeter. The material of the comet hair and tail is extremely thin, and its mass is only 1% to 5% of the total quality difference, or even less.

A comet is a small, small, cloudy object that orbits the Sun in an oblate elongated orbit (very few in a near-circular orbit).

There are three types of orbits of comets: elliptical, parabolic, and hyperbola. Comets with elliptical orbits are also called periodic comets, and the other two orbits are called non-periodic comets. Periodic comets, in turn, are divided into short-period comets and long-period comets.

Generally, comets consist of a comet head and tail. The head of the comet consists of two parts, the nucleus and the coma, and some also have the comet cloud. Not all comets have structures such as a nucleus, a comet, a tail, etc.

In ancient China, the shape of comets has been very studied, and there are 29 comet maps painted on the silk book unearthed from the ancient tomb of the Western Han Dynasty in Mawangdui, Changsha. In the Jin book "Astronomical Chronicles", it is clearly stated that comets do not emit light, but are seen by us because they reflect the sun's light, and the direction of the comet's tail is facing away from the sun. Comets are huge, but their masses are pitifully small, and even large comets are less than 1/10,000th the mass of Earth.

Since the comet is composed of various impurities and dust that are frozen, when it is far from the sun, it is just a small speck in the shape of a cloud; And when it is close to the sun, due to the evaporation, vaporization, expansion, and eruption of the condensed solid, it produces a comet tail. The tail of the comet is extremely large, and can be hundreds of millions of kilometers long. It comes in a variety of shapes, some with more than one, and generally always extends in the direction of the opposite sun, and the closer it is to the sun, the longer the comet's tail becomes.