What is the classification of celestial bodies in constellations?

All objects in the universe are celestial bodies, such as comets, which are composed of frozen impurities and dust. Astronomers vividly call it a "dirty snowball". When it runs near the sun, under the action of sunlight and heat, the dirty snow, solidified gas and ice on the outer layer of the "dirty snowball" quickly evaporate, gasify, expand and erupt. At this time, the volume of the comet expanded rapidly and was obviously divided into two parts: the head and the tail of the comet. The brightest part in the center of the comet's head is the nucleus, which is the main body of the "dirty snowball"; The substance vaporized and erupted on the surface of the nucleus is wrapped around the nucleus, forming a coma. The coma is also covered with a thin layer of hydrogen cloud, called comet cloud. The tail dragging behind the coma head is the coma tail, which is formed because the gas, dust and other substances in the coma head are pushed out by the strong radiation pressure of the sun and the solar wind. So the tail always turns its back on the sun, and the closer it is to the sun, the longer it is.

Asteroids are celestial bodies orbiting the sun, but they are too small to be called planets. Asteroids can be as big as ceres, with a diameter of about 1000 km, or as small as pebbles. There are 16 asteroids with a diameter of more than 240 kilometers. They are located in space from Earth's orbit to Saturn's orbit. Most asteroids are concentrated in the asteroid belt between the orbits of Mars and Jupiter. Some asteroids' orbits intersect with the Earth's orbit, and some asteroids have collided with the Earth.

Asteroids are remnants of the solar system. One guess is that they are the remains of a planet that was destroyed in a huge collision a long time ago. However, these asteroids are more like matter that never formed a single planet. In fact, if all the asteroids are added together to form a single celestial body, its diameter is less than 1500 km-smaller than the radius of the moon.

Because asteroids are materials of the early solar system, scientists are very interested in their composition. When the space probe passed through the asteroid belt, it was found that the asteroid belt was actually very empty and the asteroids were far apart. The asteroid data obtained before 199 1 year were only observed on the ground. 199 1 In June, Galileo Jupiter visited asteroid 95 1 Gaspula, thus obtaining the first high-resolution asteroid photo. 1In August, 993, Galileo flew over the asteroid 243 Ida, becoming the second asteroid visited by a spaceship. Gaspra and Ida asteroids are both rich in metals and belong to S-type asteroids.

We have learned a lot about asteroids by analyzing the space junk falling on the earth's surface. Those asteroids that collide with the earth are called meteoroids. When a meteoroid intrudes into our atmosphere at high speed, its surface vaporizes due to the high temperature generated by friction with air, and gives off strong light, which is a meteor. If a meteoroid does not burn completely and falls to the ground, it is called a meteorite. Hey? Through the analysis of all meteorites, 92.8% of them are silica (rocks), 5.7% are iron and nickel, and the rest are a mixture of these three substances. Meteorites with high stone content are called meteorites, and meteorites with high iron content are called meteorites. Because meteorites are very similar to earth rocks, it is difficult to distinguish them.

1On June 27th, 997, the near-earth probe passed by the 253 Mathilde asteroid. This opportunity enabled scientists to observe this carbon-rich C-type asteroid for the first time. This visit is the only one, because the near-earth detector is not specially used to check it. NEAR was used to investigate the Eros asteroid in 1999+ 10.

Astronomers have made ground observations on many asteroids. Some famous asteroids are Toutais, Castalia, Vesta and Geographos. For asteroids Toutatis, Castalia and Geographos, astronomers study them by radio observation on the ground when they are close to the sun. Vesta asteroid discovered by Hubble Space Telescope.

The discovery of asteroids is closely related to the proposition of Titius-Bode law. According to this law, there should be a planet 2.8 astronomical units away from the sun. 180 1 On New Year's Day, Piacci really discovered the first asteroid ceres there. In the following years, Venus, Venus and Vesta with orbits similar to Ceres were discovered one after another. With the introduction of astrophotography and the use of flash comparator, the annual discovery rate of asteroids has been greatly improved. By 1940, there are 1564 asteroids permanently numbered. Among them, German astronomers Cohen and Hansen have made great contributions because they are good at orbit calculation, while Wolff and Reinmus have made many discoveries in their observations.

The naming right of asteroids belongs to the discoverer. In the early days, I liked to use the name of the goddess, and later changed it to the abbreviation of people's names, places, flowers and even institutions. Some asteroid groups and asteroids are particularly famous, such as Toroyan Group, Apollo Group, Icarus, eros, Kildargo and so on. According to the statistical analysis of orbital elements, the number of asteroids with orbital inclination of about 5 degrees and eccentricity of about 0. 17 is the largest. According to the average heliocentric distance of asteroids, the Kirkwood gap is the most famous distribution feature. There is a statistical relationship between the number n of asteroids and the average magnitude m of solar eclipse, logN=0.39m-3.3, and the statistical formula logd (km) =3.7-0.2g between the diameter d of asteroids and the absolute magnitude g. The distribution of the number of asteroids with the diameter is discontinuous around the diameter of 30 km.

There are many satellites, and only Io 1 is introduced here. Io was discovered by Galileo and Marius in 16 10.

Unlike satellites in the outer solar system, Io and Europa are similar in composition to terrestrial planets and are mainly composed of hot silicate rocks. Galileo's recent data show that Io has an iron core (possibly mixed with iron sulfide) with a radius of at least 900 kilometers.

The surface of Io is different from other stars in the solar system, which surprised Voyager scientists at first contact. They believe that Earth-like stars should be covered with craters of all sizes left by the impact, and then the age of the planet's crust can be estimated by the "craters" left in the unit area. But in fact, there are only a handful of craters on Io's surface. In this way, the surface is very young.

Besides craters, Voyager 1 has discovered hundreds of craters, some of which are still active! Feather ejecta are as high as 300 kilometers. These amazing photos were sent back by Galileo (below) and Voyager (right). This may be the most important discovery in Voyager's mission, and it is also the first time to actually prove the heat and activity inside the Earth-like star. These substances seem to be ejected from the crater in the form of sulfur or sulfur dioxide. The volcano erupted quite quickly, but in the four months after the arrival of Voyager 1 and Voyager 2, some activities stopped and others started again. The deposits around the nozzle also changed obviously.

According to recent photos taken from NASA's infrared telescope equipment in Mauna Kea Mountain, Hawaii, Io has a huge new volcanic eruption (right). The new situation in La Patra has been seen by Hubble telescope. Photographs from Galileo also show some changes in its surface since Voyager came into contact with it. These observations prove that Io's surface is indeed quite active.

Io has amazing terrain: there are craters thousands of meters deep, fiery sulfur lakes (lower right), obvious non-volcanic mountains (left), and hundreds of kilometers of viscous liquid (some form of sulfur? ), and some craters. The colors of sulfur and its compounds make Io's surface colorful.

The analysis of Voyager's photos convinced scientists that the lava flow on Io's surface was mostly composed of hot sulfur compounds. However, subsequent research based on the surface shows that the temperature there is too high and there will be no liquid sulfur. At present, there is a theory that Io's lava flow is composed of hot silicate rocks. Recent observations by Hubble telescope show that those substances may be rich in sodium, or that substances in different places there have different compositions.

The hottest temperature on Io's surface can reach 1500 Kelvin, although its average temperature is only about 130 Kelvin. These hot spots are the main reason why Io loses heat.

The energy needed for all its activities may come from tidal force, which interacts with Europa, Ganymede and Jupiter. The dynamic relationship between these three satellites is fixed. The period of revolution of Io is twice that of Europa, and the latter is twice that of Ganymede. Although Io, like the moon, the satellite of the earth, only faces its main star with a fixed side, it is a little unstable because of the role of Europa and Ganymede. It makes Io twist and bend, about 100 meters long (100 spring tide! ) and generates energy in the cycle of restoring distortion. The moon is not heated by the earth in this way because it lacks another star to disturb it. )

Io also cuts Jupiter's magnetic field lines to generate electricity. For tidal power generation, the energy generated is not much, but the current power is still 1 MW. It also stripped off some Io material, which produced strong convex radiation around Jupiter. The particles separated from the convex surface partially create Jupiter's huge magnetosphere.

Recent data from Galileo show that Io may have its own magnetic field, just like Ganymede.

Io's atmosphere is very thin and consists of sulfur dioxide and other gases.

Unlike other satellites discovered by Galileo, Io has almost no water. This may be because Jupiter was too hot at the beginning of the evolution of the solar system, which made the volatile substances near Io evaporate, but it was not hot enough to squeeze out all the water.

star

Looking at the night sky from the earth, the universe is a world of stars.

The distribution of stars in the universe is uneven. From the day they were born, they gathered in groups and reflected each other, forming binary stars, clusters and galaxies. ...

A star is a burning planet. Generally speaking, the volume and mass of stars are relatively large. It is only because it is too far away from the earth that the starlight appears so weak.

Ancient astronomers thought that the position of a star in the starry sky was fixed, so they named it "Star", which means "Eternal Star". But today we know that they have been moving at high speed. For example, the sun takes the whole solar system around the center of the Milky Way. But other stars are too far away from us, and it is difficult for us to detect the changes in their positions.

The ability of stars to shine is strong and weak. Astronomy is expressed by "luminosity". The so-called "luminosity" refers to the energy radiated by the surface of a star in the form of light. There are also high and low temperatures on the surface of stars. Generally speaking, the lower the surface temperature of a star, the redder its light; The higher the temperature, the bluer the light. The higher the surface temperature, the larger the surface area and the greater the luminosity. Scientists can extract a lot of useful information from the color and luminosity of stars.

Historically, astronomer hertzsprung and philosopher Russell first put forward the relationship between star classification and color and luminosity, established a star evolution relationship named "Herzog-Roto", and revealed the secret of star evolution. In "Herro-Roto", from the high-temperature strong light area at the upper left to the low-temperature weak light area at the lower right, it is a narrow star-intensive area, and our sun is also in it; This sequence is called the main sequence, and more than 90% stars are concentrated in the main sequence. Above the main sequence area are the giant star and Supergiant star area; On the lower left is the white dwarf region.

Stars are born from interstellar dust in space (scientists call it "nebula" or "interstellar cloud").

The "youth" of a star is the longest golden stage in his life-the main sequence stage, which accounts for 90% of his life. During this period, the stars emit light and heat with almost constant luminosity, illuminating the surrounding space.

Then the star will become turbulent and become a red giant; Then, the red giant will complete all tasks in the explosion, throwing most of the matter back into space, leaving behind debris, perhaps white dwarfs, perhaps neutron stars, or even black holes. ...

In this way, the star came out of the nebula and returned to the nebula, completing its brilliant life.

Gorgeous stars are always the most beautiful scenery in the night sky.

Nebulae are remnants of the explosion of stars.

Solar System The solar system is a celestial system consisting of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors. The solar system is a celestial system composed of the sun, planets and their satellites, asteroids, comets, meteors and interplanetary matter, and the sun is the center of the solar system. In the huge solar system family, the mass of the sun accounts for 99.8% of the total mass of the solar system, and the proportion of nine planets and tens of thousands of asteroids is very small. They have been running around the sun along their own orbits for ages, and at the same time, the sun has generously and selflessly contributed its own light and heat, warming every member of the solar system and promoting their continuous development and evolution.

In this family, the planet closest to the sun is Mercury, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Only five stars can be seen by the naked eye. The names of these five stars are different in different countries. There was a theory of five elements in ancient China, so the five elements of gold, wood, water, fire and earth were used to name Venus, Jupiter, Mercury, Mars and Saturn respectively. This is not because there is water on Mercury and trees on Jupiter. On the other hand, Europe calls Roman mythical figures by their names. The three distant planets discovered in modern times are called by the names of the gods of the sky, the ocean and the earth according to the tradition of naming mythical figures in the west, and are correspondingly translated into Uranus, Neptune and Pluto in Chinese.

The nine planets and the sun are the sun, Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury and Pluto in descending order. According to the standards of mass, size, chemical composition and distance from the sun, it can be roughly divided into three categories: terrestrial planets; Giant planets (Jupiter and Saturn); The distant planets Uranus, Neptune and Pluto. When they rotate, they have the characteristics of * * * plane, same direction and approximate circle. There are hundreds of thousands of asteroids of different sizes and shapes between Mars and Jupiter. Astronomy calls this area the asteroid belt. In addition, the solar system also includes many comets and countless whispers-meteors.

Galaxy system

The star system in which the solar system is located includes120 billion stars, a large number of star clusters and nebulae, and various types of interstellar gas and dust. Its total mass is 654.38+04 billion times that of the sun. Most stars in the Milky Way are concentrated in a oblate sphere, which is shaped like a discus. The protruding part in the middle of the oblate sphere is called the "nuclear sphere" with a radius of about 7000 light years. The center of the core ball is called "silver core" and the periphery is called "silver disk". There is a bigger sphere outside the silver disk, where there are fewer stars and less density. It is called "Silver Halo" with a diameter of 70,000 light years. The Milky Way is a spiral galaxy with a spiral structure, that is, it has a silver center and two spiral arms, which are 4500 light years apart. The rotation speed and period of each part of it are different because the distance from the silver center is different. The sun is about 23,000 light years away from the galactic center, and it orbits the galactic center at a speed of 250 km/s with a period of about 250 million years.

universe

The day when the energy in all matter in the universe is exhausted is the day when the material universe dies. All matter in the universe is decomposed into a confinement field ("Yin") and an energy field ("Yang"), and temperature of the universe is the lowest at this time. The average energy density is the lowest; The universe expands to the maximum; Naked singularity black holes meet farthest; The potential energy of primitive gravity reaches its maximum. At this time, the universe is already dark, and the universe expands to the largest torus, which is covered with billions of dead galaxies and degenerates into naked singularity confinement fields or dark galaxies. This is the end of the physical universe.

meteor

When the meteor swarm meets the earth, the number of meteors increases significantly within a few hours to a few days, sometimes even like rain. This phenomenon is called meteor shower. Meteor trajectories observed during a meteor shower extend in the opposite direction and all meet at one point, which is called radiation point. Most meteor showers are named after the constellation where the radiant point is located or the bright stars nearby, such as "Leonid Meteor Shower". A few meteor showers are named after related comets, such as "comet Bila meteor shower". When a meteor shower occurs, the frequency of meteors is usually ten to dozens per hour, but in a few cases it can reach thousands per hour. This phenomenon is called star rain. Meteor shower is a periodic phenomenon, and its appearance date is basically fixed. However, due to the uneven distribution of meteoroids in orbit, the number of meteors in a meteor shower varies from year to year. For example, the Leonid meteor shower is generally small in scale, and there will be different degrees of star rain every 33 years.

meteor

Meteorites are "guests" from outside the earth. According to the different chemical composition of meteorites, they can be roughly divided into three types:

1. Iron meteorites, also called meteorites, are mainly composed of iron and nickel;

2. Stone iron meteorites, also known as stone iron, are relatively rare, of which iron, nickel and silicate account for about half;

3. Stone meteorites, also known as meteorites, are mainly composed of silicates, and the number of such meteorites is the largest.

Meteorites contain a lot of information about the formation and evolution of celestial bodies in the solar system, and their experimental analysis will help to explore the mystery of the evolution of the solar system. Meteorites are composed of chemical elements known on the earth, and water and various organic substances are found in some meteorites. This has become a basis for the hypothesis of the origin of life that "life on earth is the seed of life spread from meteorites to the earth". By measuring the isotopic contents of various elements in meteorites, we can calculate the age of meteorites, and then calculate the period when the solar system began to form. Meteorites may be fragments of asteroids, planets, large satellites or comets, which can carry the original information of these celestial bodies. The famous meteorites are China Jilin meteorite, China Xinjiang meteorite, American barringer meteorite, Australian murchison carbonaceous meteorite, etc.