On a clear dark night, especially in mid-August, November and December, you can see how “shooting stars” trace the sky - these are meteors, an interesting natural phenomenon known to man from time immemorial.

Meteors, especially in recent years, have attracted the close attention of astronomical science. They have already told a lot about our solar system and about the Earth itself, in particular about the earth's atmosphere.

Moreover, meteors, figuratively speaking, returned the debt, reimbursed the funds spent on their study, making a contribution to the solution of some practical problems of science and technology.

The study of meteors is being actively developed in a number of countries, and our short story is devoted to some of these studies. Let's start with a clarification of terms.

An object moving in interplanetary space and having dimensions, as they say, “larger than molecular, but less than asteroidal,” is called a meteoroid, or meteoroid. Invading the earth's atmosphere, a meteoroid (meteoroid) heats up, glows brightly and ceases to exist, turning into dust and vapor.

The light phenomenon caused by the combustion of a meteoroid is called a meteor. If the meteoroid has a relatively large mass and if its speed is relatively low, then sometimes a part of the meteoroid, without having had time to completely evaporate in the atmosphere, falls to the Earth's surface.

This fallen part is called a meteorite. Extremely bright meteors, which look like a fireball with a tail or a burning firebrand, are called fireballs. Bright fireballs are sometimes visible even during the day.

Why study meteors

Meteors have been observed and studied for centuries, but only in the last three or four decades have the nature, physical properties, characteristics of orbits and the origin of those cosmic bodies that are sources of meteorites become clearly understood. The interest of researchers in meteor phenomena is associated with several groups of scientific problems.

First of all, the study of the trajectory of meteors, the processes of luminescence and ionization of the matter of meteoroids, is important for clarifying their physical nature, and they, meteor bodies, after all, are “trial portions” of matter that arrived at the Earth from distant regions of the solar system.

Further, the study of a number of physical phenomena accompanying the flight of a meteor body provides rich material for studying the physical and dynamic processes occurring in the so-called meteor zone of our atmosphere, that is, at altitudes of 60-120 km. This is where meteors are mostly observed.

Moreover, for these layers of the atmosphere, meteors, perhaps, remain the most effective "research tool", even against the background of the current scope of research using spacecraft.

Direct methods for studying the upper layers of the earth's atmosphere using artificial Earth satellites and high-altitude rockets began to be widely used many years ago, since the International Geophysical Year.

However, artificial satellites provide information about the atmosphere at altitudes above 130 km; at lower altitudes, satellites simply burn up in the dense layers of the atmosphere. As for rocket measurements, they are carried out only over fixed points on the globe and are of a short-term nature.

Meteor bodies are full-fledged inhabitants of the solar system, they circulate in geocentric orbits, which usually have the shape of an ellipse.

Estimating how the total number of meteoroids is distributed among groups with different masses, velocities, directions, one can not only study the entire complex of small bodies of the solar system, but also create a basis for constructing a theory of the origin and evolution of meteoric matter.

AT recent times interest in meteors has also increased in connection with the intensive study of near-Earth space. An important practical task was the assessment of the so-called meteor hazard on various space paths.

This, of course, is only a private issue, space and meteor research have a lot of common ground, and the study of meteor particles has firmly entered the space programs. So, for example, with the help of satellites, space probes and geophysical rockets, valuable information was obtained about the smallest meteoroids moving in interplanetary space.

Here is just one figure: the sensors installed on spacecraft make it possible to register impacts of meteoroids, the dimensions of which are measured in thousandths of a millimeter (!).

How meteors are observed

On a clear moonless night, meteors up to the 5th and even 6th magnitude can be seen - they have the same brightness as the faintest stars visible to the naked eye. But mostly, slightly brighter meteors, brighter than 4th magnitude, are visible to the naked eye; about 10 such meteors can be seen on average within an hour.

In total, there are about 90 million meteors in the Earth's atmosphere per day, which could be seen at night. The total number of meteoroids of various sizes that invade the earth's atmosphere per day is in the hundreds of billions.

In meteor astronomy, it has been agreed to divide meteors into two types. Meteors that are observed every night and move in a variety of directions are called random, or sporadic. Another type is periodic, or streaming, meteors, they appear at the same time of the year and from a certain small area of ​​​​the starry sky - the radiant. The word is - radiant - in this case means "radiating area."

Meteor bodies that give rise to sporadic meteors move in space independently of each other along the most diverse orbits, and periodic ones along almost parallel paths, which just emanate from the radiant.

Meteor showers are named after the constellations in which their radiants are located. For example, the Leonids are a meteor shower with a radiant in the constellation Leo, the Perseids are in the constellation Perseus, the Orionids are in the constellation of Orion, and so on.

Knowing the exact position of the radiant, the moment and speed of the meteor, it is possible to calculate the elements of the meteoroid's orbit, that is, to find out the nature of its movement in interplanetary space.

Visual observations made it possible to obtain important information about the daily and seasonal changes in the total number of meteors, and about the distribution of radiants over the celestial sphere. But mainly photographic, radar, and, in recent years, electron-optical and television methods of observation are used to study meteors.

The systematic photographic recording of meteors began about forty years ago; the so-called meteor patrols are used for this purpose. A meteor patrol is a system of several photographic units, and each unit usually consists of 4-6 wide-angle photographic cameras, installed so that all of them together cover the maximum possible area of ​​the sky.

Observing a meteor from two points 30-50 km apart, it is easy to determine its height, trajectory in the atmosphere and radiant from photographs against the background of stars.

If an obturator, that is, a rotating shutter, is placed in front of the cameras of one of the patrol units, then the speed of the meteoroid can also be determined - instead of a continuous trace, a dotted line will appear on the film, and the length of the strokes will be exactly proportional to the speed of the meteoroid.

If prisms or diffraction gratings are placed in front of the camera lenses of another unit, then the spectrum of a meteor will appear on the plate, just as the spectrum of a sunbeam that has passed through a prism appears on a white wall. And from the spectra of the meteor, you can determine the chemical composition of the meteoroid.

One of the important advantages of radar methods is the ability to observe meteors in any weather and around the clock. In addition, radar makes it possible to register very faint meteors up to 12-15 magnitude, generated by meteoroids with a mass of millionths of a gram or even less.

The radar “detects” not the meteor body itself, but its trace: when moving in the atmosphere, the evaporated atoms of the meteoroid collide with air molecules, are excited and turn into ions, that is, mobile charged particles.

Ionized meteor trails are formed, having a length of several tens of kilometers and initial radii of the order of a meter; these are a kind of hanging (of course, not for long!) atmospheric conductors, or more precisely semiconductors - in them one can count from 106 to 1016 free electrons or ions per centimeter of track length.

Such a concentration of free charges is quite enough to reflect radio waves of the meter range from them, as from a conducting body. Due to diffusion and other phenomena, the ionized trail rapidly expands, its electron concentration falls, and under the influence of winds in the upper atmosphere, the trail dissipates.

This makes it possible to use radar to study the speed and direction of air currents, for example, to study the global circulation of the upper atmosphere.

In recent years, observations of very bright fireballs, which are sometimes accompanied by meteorites, have been increasingly observed. Fireball observation networks with "all-sky" cameras are organized in several countries.

They do control the entire sky, but they only register very bright meteors. Such networks include 15-20 points located at a distance of 150-200 kilometers, they cover large areas, since the invasion of the earth's atmosphere by a large meteoroid is a relatively rare phenomenon.

And here's what's interesting: of the photographed several hundred bright fireballs, only three were accompanied by a meteorite fall, although the speeds of large meteoroids were not very large. This means that the above-ground explosion of the Tunguska meteorite in 1908 is a typical phenomenon.

Structure and chemical composition of meteoroids

The intrusion of a meteoroid into the earth's atmosphere is accompanied by complex processes of its destruction - melting, evaporation, dispersion and crushing. Atoms of meteor matter upon collision with air molecules are ionized and excited: the glow of a meteor is mainly associated with the radiation of excited atoms and ions, they move at the speeds of the meteoric body itself and have a kinetic energy from several tens to hundreds of electron volts.

Photographic observations of meteors using the method of instantaneous exposure (about 0.0005 sec.), developed and implemented for the first time in the world in Dushanbe and Odessa, clearly showed various types of fragmentation of meteoroids in the earth's atmosphere.

Such fragmentation can be explained both by the complex nature of the processes of destruction of meteoroids in the atmosphere, and by the loose structure of meteoroids and their low density. The density of meteor bodies of cometary origin is especially low.

The spectra of meteors mainly show bright emission lines. Among them, lines of neutral atoms of iron, sodium, manganese, calcium, chromium, nitrogen, oxygen, aluminum, and silicon, as well as lines of ionized atoms of magnesium, silicon, calcium, and iron, were found. Like meteorites, meteoroids can be divided into two large groups - iron and stone, and there are much more stone meteoroids than iron ones.

Meteor matter in interplanetary space

An analysis of the orbits of sporadic meteoroids shows that the meteoric matter is concentrated mainly in the ecliptic plane (the plane in which the orbits of the planets lie) and moves around the Sun in the same direction as the planets themselves. This is an important conclusion, it proves the common origin of all the bodies of the solar system, including such small ones as meteoroids.

The observed speed of meteoroids relative to the Earth is in the range of 11-72 km/sec. But the speed of the Earth in its orbit is 30 km/sec, which means that the speed of meteoroids relative to the Sun does not exceed 42 km/sec. That is, it is less than the parabolic velocity required to exit the solar system.

Hence the conclusion - meteoroids do not come to us from interstellar space, they belong to the solar system and move around the Sun in closed elliptical orbits. Based on photographic and radar observations, the orbits of several tens of thousands of meteoroids have already been determined.

Along with the gravitational attraction of the Sun and planets, the movement of meteoroids, especially small ones, is significantly influenced by forces caused by the influence of the electromagnetic and corpuscular radiation of the Sun.

So, in particular, under the influence of light pressure, the smallest meteor particles smaller than 0.001 mm in size are pushed out of the solar system. In addition, the motion of small particles is also significantly affected by the decelerating effect of radiation pressure (the Poynting-Robertson effect), and because of this, the orbits of the particles are gradually "shrinking", they are getting closer and closer to the Sun.

The lifetime of meteoroids in the inner regions of the solar system is short, and, therefore, the reserves of meteoric matter must somehow be constantly replenished.

There are three main sources of such replenishment:

1) the decay of cometary nuclei;

2) fragmentation of asteroids (recall, these are small planets moving mainly between the orbits of Mars and Jupiter) as a result of their mutual collisions;

3) the influx of very small meteoroids from the distant environs of the solar system, where, probably, there are remnants of the substance from which the solar system was formed.

Meteorites are rocks that fall from the sky. Most of them are from the era of the formation of the solar system, but some of them come to us from the moon and even from Mars.

Between the planets is a surprisingly large amount of space debris. Most often this is the residual material formed during the formation of the planets, but some of it is of relatively recent origin, such as the dusty tails left by comets. Astronomers use three similar words to refer to this material: meteoroid, meteor, and meteorite.

A meteor body is a piece of stone or an accumulation of sting in outer space. The surface of the Earth is constantly bombarded by celestial bodies of various sizes: from dust particles to stones weighing several kilograms. These bodies break into the atmosphere at a speed of 60,000 km / h or more. As a result of friction against the air, objects become hot and flash with a fiery red sung. A meteor is a visible trail in the sky left by an erupting object as it enters the atmosphere. These trails are also called shooting stars. A meteor body that reaches the earth's surface is called a meteorite. Often, meteorites are given names but to the place where they fell.

Making its annual journey around the Sun, the Earth sweeps away about 1000 tons of space rock and ache on its way. Much of this material rotates in the solar system in the form of a stream that occurs when a comet rushes through the solar system, leaving behind a tail of rock debris. When the Earth passes through such a note, meteor showers are seen in the sky. From grains of dust burning in the atmosphere, in the sky flare-1 from bright lines that seem to come from one point. The occurrence of meteor showers can be fairly accurately predicted, since the Earth crosses meteor showers at more or less the same time each year.

Stones that safely reach the Earth, flying in flames through the entire atmosphere, are not so common. A rough estimate of the annual amount of such material falling on the Earth's surface is 200 swamps, and almost all of this is in the form of very fine grains of dust. Only about 20 new meteorites are found each year. The radioactivity of meteorites shows that they formed 4.6 billion years ago as part of the solar system. Because they are samples of the primordial material of the early solar system, meteorites are very valuable to planetary scientists.

There are three main types of meteorites: those composed mainly of iron; then stone-iron, and finally stone, which may contain only a small amount of metal. Iron meteorites are the easiest to recognize because they are very dense and strong. Stony meteorites are of great interest because they have never been very hot (except for their brief fall through the atmosphere). This means that they have not changed much since their formation. Therefore, their chemical composition is similar to that of the early solar system.

So far, not a single case of death from meteorites has been recorded, although there have been cases of close danger. One meteorite fell on August 31, 1991 less than 4 meters from two boys. This happened in the state of Indiana (USA). From the impact of this meteorite, a crater 4 cm deep and 9 cm in diameter was formed. In the same year, another meteorite swept very close to a man working in his garden in England. On October 13, 1992, a large meteorite crashed an empty car in the state of New York (USA).

Large meteorites leave significant craters. The best-preserved crater is in Arizona, as the dry desert climate has protected it from erosion since its formation about 50,000 years ago. This, however, is just one of 140 meteorite craters on Earth, many of which are much larger. The age of one of the largest craters in Quebec (Kapala) is 200 million years old, its diameter is 100 km.

Currently, the main source of meteorites for scientific analysis is the ice sheet of Antarctica. There are already thousands of them. Having lain in the depths of snow and ice for up to a million years, they were exposed and were found on the surface of the mainland and in those places where strong winds tore off ice caps. The dry rocky deserts of Western Australia and Namibia are also important sources of ancient meteorites.

Comets

Large comets with tails stretching far across the sky have been observed since ancient times. Comets were once thought to be atmospheric phenomena. The movement of comets across the sky was first explained by Halley (1705), who found that their orbits are very elongated. He determined the orbits of 24 bright comets, and it turned out that the comets of 1531, 1607 and 1682. have very similar orbits. From this, Halley concluded that this is the same comet that moves around the Sun in a very elongated ellipse with a period of about 76 years. Halley predicted that in 1758 it should reappear, and in December 1758 it was indeed discovered. Halley himself did not live to see this time and could not see how brilliantly his prediction was confirmed. This comet (one of the brightest) was named after him (Fig. 4.11). Halley's comet last appeared in our sky in 1986.

Rice. 4.11. Comet Halley (Georgia, USA).

The search for comets was carried out first visually, and then from photographs, but the discoveries of comets during visual observations are often made even now. Comets are named after the names of the people who discovered them.

To date, about 1000 comets have been registered in the catalogs and the elements of their orbits have been determined. Most comets move in very elongated ellipses, almost parabolas. Comets with an elliptical orbit are called periodical , and if their period of revolution is less than 200 years, then short period, if more, then long-term.

Of the periodic comets, about 80% of their orbits are inclined by less than 45° to the plane of the ecliptic. Only Halley's comet has an orbit with an inclination greater than 90° and therefore moves in the opposite direction. The rest move in a straight line.

Among the short-period comets, the “Jupiter family” stands out - a large group of comets, the aphelia of which are at the same distance from the Sun as the orbit of Jupiter. It is assumed that the Jupiter family was formed as a result of the capture of comets by the planet, which previously moved along more elongated orbits.

The orbits of periodic comets are subject to very noticeable changes. Sometimes a comet passes near the Earth several times, and then, by the attraction of the giant planets, it is thrown into a more distant orbit and becomes unobservable. In other cases, on the contrary, a comet that has never been observed before becomes visible due to the fact that it passed near Jupiter or Saturn and changed its orbit dramatically. In addition to such abrupt changes, known only for a limited number of objects, the orbits of all comets experience gradual changes.

In the structure of a comet, the following constituent elements are distinguished: the nucleus, the head and the tail.

Core comets are a small solid icy body, including refractory particles and organic compounds. Almost the entire mass of a comet is concentrated in the nucleus. Up to 80% of the comet's nucleus consists of water ice, as well as frozen carbon dioxide, carbon monoxide, methane, ammonia and metal particles interspersed in them. The cores range in size from a few hundred meters to several hundred kilometers.

As the comet approaches the Sun within a few AU, the ice begins to evaporate. In this case, the evaporating gas entrains dust particles. The comet forms head , the diameter of which can reach sizes 10 4 -10 6 km. Under the action of light pressure, the trajectories of molecules and dust particles deviate and go in the direction opposite to the Sun, forming tail . The tails of bright comets stretch for hundreds of millions of kilometers. Sometimes there is a so-called anti-tail directed towards the Sun. This is a large dust leaving in the plane of the orbit.

Each return of a comet to the Sun does not pass without a trace. The brightness of short-period comets decreases with time. The nucleus of a comet loses about 1/1000 of its mass. Therefore, for example, the lifetime of Halley's comet is estimated at 20 thousand years. But comets can exist even smaller. They can die in collisions with planets, meteorite bodies. In some cases, the process of destruction of comets was observed almost directly.

The question of the origin of comets has not yet been studied enough. According to the hypothesis of the Dutch scientist Oort, the solar system is surrounded by a giant cloud of cometary nuclei, extending up to 1 ps(Oort cloud). Under the influence of stellar perturbations, the orbits of some nuclei change, and as a result, comets appear near the Sun. Some of the short-period comets may come from the Kuiper belt.

Meteora(Fig. 4.12) are observed in the form of short-term flashes that sweep across the sky and disappear, sometimes leaving a narrow luminous trail for several seconds. Often in everyday life they are called shooting stars. For a long time, astronomers were not at all interested in meteors, considering them to be an atmospheric phenomenon such as lightning. Only at the very end of the XVIII century. as a result of observations of the same meteors from different points, their heights and speeds were determined for the first time. It turned out that meteors are cosmic bodies that come into the earth's atmosphere from the outside with speeds from several km/s up to several dozen km/s and burn in it at a height of about 80 km.

The frequency of meteors and their distribution across the sky is not always uniform. Systematically observed meteor showers, whose meteors over a certain period of time (several nights) appear approximately in the same region of the sky. If their traces continue backwards, then they will intersect near one point, called radiant meteor shower. Many meteor showers are periodic, repeat year after year, and are named after the constellations in which their radiants lie. Thus, the meteor shower, which operates annually from about July 20 to August 20, is called the Perseids, since its radiant lies in the constellation Perseus. The Lyrid (mid-April) and Leonid (mid-November) meteor showers are named after the constellations Lyra and Leo, respectively.

Rice. 4.12. Photo of a meteor. The Pleiades star cluster is visible on the left side.

The activity of meteor showers varies from year to year. There are years in which the number of meteors belonging to the stream is very small, and in other years (repeating, as a rule, with a certain period) it is so abundant that the phenomenon itself is called star rain. The last stellar showers were observed in August 1961 (Perseids) and in November 1966 (Leonids). The changing activity of meteor showers is explained by the fact that meteor particles in the streams are unevenly scattered along an elliptical orbit that crosses the earth's.

Meteors that do not belong to streams are called sporadic. The statistical distribution of the orbits of sporadic meteors has not been studied exactly, but there is reason to believe that it is similar to the distribution of the orbits of periodic comets. As for meteor showers, many of them have orbits close to those of known comets. Cases are known when a comet disappeared, but the meteor shower associated with it remained (Biela's comet). All this makes us think that meteor showers result from the destruction of comets.

During the day, about 10 8 meteors brighter than 5 m flare up in the Earth's atmosphere. Bright meteors are observed less often, weak ones more often. Very bright meteors fireballs may be observed during the day. Fireballs are sometimes accompanied by loss meteorites. The appearance of a fireball may be accompanied by a more or less strong shock wave, sound phenomena and the formation of a smoke tail.

The spectra of meteors consist of emission lines. When a meteor particle slows down in the atmosphere, it heats up, begins to evaporate, and a cloud of hot gases forms around it. It is mainly metal lines that glow: very often, for example, H and K lines of ionized calcium and iron lines are observed. Apparently, the chemical composition of meteor particles is similar to the composition of stone and iron meteorites, but the mechanical structure of meteoroids should be completely different.

meteorites, "heavenly stones" have been known to mankind for a very long time. Apparently, the appearance of the first iron tools, which played a huge role in the evolution of prehistoric cultures, is associated with the use of meteoric iron. Large meteorites sometimes served as an object of worship among ancient peoples. Official science recognized their celestial origin only at the beginning of the 19th century.

With the exception of lunar rock samples brought to Earth, meteorites are so far the only cosmic bodies that can be studied in terrestrial laboratories. It is clear that the collection and study of meteorites is of great scientific importance.

Meteorites are divided into three large groups according to their chemical composition and structure: stone(aerolites), iron-stone(siderolites) and iron(siderites). The question of the relative abundance of different types of meteorites is not entirely clear, since iron meteorites are easier to find than stony ones, and, in addition, stony meteorites are more easily destroyed when passing through the atmosphere. Most researchers believe that stony meteorites predominate in outer space (80-90% of the total), although more iron meteorites have been collected than stony ones.

Since fireballs are a rare phenomenon, the orbits of meteorite bodies have to be determined from inaccurate testimonies of random eyewitnesses, and therefore there are no reliable data on the orbits of fallen meteorites. According to the radiants of the fireballs accompanied by the fallout of meteorites, it can be concluded that most of them moved in the forward direction, and their orbits are characterized by a small inclination.

When a meteorite body enters the dense layers of the atmosphere, its surface heats up so much that the substance of the surface layer begins to melt and evaporate. Air jets blow off large drops of molten substance from the surface of iron meteorites, and traces of this blowing off remain in the form of characteristic recesses. Stony meteorites often break up, and then a whole rain of fragments of various sizes falls to the surface of the Earth. Iron meteorites are stronger, but they also sometimes break into separate pieces. One of the largest iron meteorites, the Sikhote-Alin, which fell on February 12, 1947, was found in the form of a large number of individual fragments. The total weight of the collected fragments reached 23 t, and, of course, not all fragments were found. The largest known meteorite, Goba (Southwest Africa), is a block weighing 60 t.

Large meteorites, hitting the Earth, burrow to a considerable depth. However, the cosmic velocity is usually extinguished in the atmosphere at a certain height and, having slowed down, the meteorite falls according to the laws of free fall. What happens if an even larger mass collides with the Earth, for example 10 5 -10 8 t? Such a giant meteorite would have passed through the atmosphere almost unhindered, when it fell, a strong explosion would have occurred and a funnel (crater) would have formed. If such catastrophic phenomena have ever occurred, then we should find meteorite craters on the earth's surface. Such craters do exist. The largest of them is the Arizona crater (Fig. 4.13), the funnel of which has a diameter of 1200 m and a depth of about 200 m. Its age, according to a rough estimate, is about 5000 years. Recently, a number of more ancient and destroyed meteorite craters have been discovered.

Rice. 4.13. Arizona meteorite crater.

The chemical composition of meteorites has been well studied. Iron meteorites contain on average 91% iron, 8.5% nickel, and 0.6% cobalt; stony meteorites - 36% oxygen, 26% iron, 18% silicon and 14% magnesium. Stony meteorites are close to the earth's crust in terms of oxygen and silicon content, but they contain much more metals. The content of radioactive elements in meteorites is less than in the earth's crust, and in iron it is less than in stone. The age of meteorites can be determined from the relative content of radioactive elements and their decay products. For different samples, it turns out to be different and usually ranges from several hundred million to several billion years.

Since ancient times, there has been a belief that if you make a wish while looking at a shooting star, it will surely come true. Have you thought about the nature of the phenomenon of shooting stars? In this lesson, we will discover what is star rain, meteorites and meteors.

Theme: Universe

Lesson: Meteors and meteorites

Phenomena observed in the form of short-term flashes that occur during the combustion in the earth's atmosphere of small meteor objects (for example, fragments of comets or asteroids). Meteors streak across the sky, sometimes leaving behind them a narrow glowing trail for a few seconds before disappearing. In everyday life they are often called shooting stars. For a long time, meteors were considered a common atmospheric phenomenon such as lightning. Only at the very end of the 18th century, thanks to the observations of the same meteors from different points, were their heights and speeds determined for the first time. It turned out that meteors are cosmic bodies that come into the Earth's atmosphere from outside at speeds from 11 km/sec to 72 km/sec, and burn up in it at an altitude of about 80 km. Astronomers began to seriously engage in the study of meteors only in the 20th century.

The distribution across the sky and the frequency of occurrence of meteors are often not uniform. So-called meteor showers occur systematically, the meteors of which appear in approximately the same part of the sky over a certain period of time (usually several nights). Such streams are assigned the names of constellations. For example, the meteor shower that occurs every year from about July 20 to August 20 is called the Perseids. The Lyrid (mid-April) and Leonid (mid-November) meteor showers take their names from the constellations Lyra and Leo, respectively. In different years, meteor showers show different activity. The change in the activity of meteor showers is explained by the uneven distribution of meteor particles in the streams along an elliptical orbit crossing the Earth.

Rice. 2. Perseid meteor shower ()

Meteors that do not belong to streams are called sporadic. In the Earth's atmosphere, on average, about 108 meteors brighter than 5 magnitude flare up during the day. Bright meteors occur less often, weak ones more often. Fireballs(very bright meteors) can be seen even during the day. Sometimes fireballs are accompanied by meteorites. Often, the appearance of a fireball is accompanied by a rather powerful shock wave, sound phenomena, as well as the formation of a smoke tail. The origin and physical structure of the large bodies observed as fireballs is probably quite different from the particles that cause meteor phenomena.

Distinguish between meteors and meteorites. A meteor is not the object itself (that is, a meteoroid), but a phenomenon, that is, its luminous trail. This phenomenon will be called a meteor, regardless of whether the meteoric body flies out of the atmosphere into outer space, whether it burns up in it or falls to Earth in the form of a meteorite.

Physical meteorology is the science that studies the passage of a meteorite through the layers of the atmosphere.

Meteor astronomy is the science that studies the origin and evolution of meteorites.

Meteor geophysics is the science that studies the effect of meteors on the Earth's atmosphere.

- a body of cosmic origin that fell on the surface of a large celestial object.

According to their chemical composition and structure, meteorites are divided into three large groups: stone, or aerolites, stony-iron, or siderolites, and iron - siderites. Most researchers agree that stony meteorites predominate in outer space (80-90% of the total), although more iron meteorites have been collected than stony meteorites. The relative abundance of different types of meteorites is difficult to determine, since iron meteorites are easier to find than stone ones. In addition, stony meteorites usually break apart as they pass through the atmosphere. When a meteorite enters the dense layers of the atmosphere, its surface heats up so much that it begins to melt and evaporate. Air jets blow off large drops of molten substance from iron meteorites, while traces of this blowing remain, and they can be observed in the form of characteristic depressions. Stony meteorites often break up, scattering a whole rain of fragments of various sizes onto the Earth's surface. Iron meteorites are more durable, but they also sometimes break into separate pieces. One of the largest iron meteorites, which fell on February 12, 1947 in the Sikhote-Alin region, was found in the form of a large number of individual fragments, the total weight of which is 23 tons, while, of course, not all fragments were found. The largest known meteorite, Goba (in South West Africa), is a block weighing 60 tons.

Rice. 3. Goba - the largest meteorite found ()

Large meteorites, when they hit the Earth, burrow to a considerable depth. At the same time, in the Earth's atmosphere at a certain height, the cosmic velocity of the meteorite is usually extinguished, after which, having slowed down, it falls according to the laws of free fall. What happens when a large meteorite, for example, weighing 105-108 tons, collides with the Earth? Such a gigantic object would pass through the atmosphere almost unhindered, and when it fell, a strong explosion would occur with the formation of a funnel (crater). If such catastrophic events ever occurred, we would have to find meteorite craters on the surface of the Earth. Such craters do exist. So, the funnel of the largest, Arizona, crater has a diameter of 1200 m and a depth of about 200 m. According to a rough estimate, its age is about 5 thousand years. Not so long ago, several more ancient and destroyed meteorite craters were discovered.

Rice. 4. Arizona meteorite crater ()

Shock crater(meteorite crater) - a depression on the surface of a cosmic body, the result of the fall of another smaller body.

Most often, a meteor shower of great intensity (with a zenith hour number of up to a thousand meteors per hour) is called a stellar or meteor shower.

Rice. 5. Star rain ()

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1. Melchakov L.F., Skatnik M.N. Natural history: textbook. for 3.5 cells. avg. school - 8th ed. - M.: Enlightenment, 1992. - p. 165, tasks and question. 3.

2. How are meteorite showers named?

3. How is a meteorite different from a meteor?

4. * Imagine that you have discovered a meteorite and want to write a magazine article about it. What would this article look like?