How stars differ from planets: details and interesting points. Such amazing and beautiful planets

Good visibility on a clear night.

planets

Among the countless stars can be easily distinguished by their brilliance planets, which is translated from ancient Greek - wandering stars. These celestial bodies were so named by the ancient Greeks because from day to day they moved relative to the seemingly motionless stars and in the night sky seemed to be bright luminaries.

Planets of the Universe

As you know, the planets are not at all: they receive light from and move around it in orbits that are close to a circle in shape.

Comets

In very elongated orbits, after a certain period of time, distant guests of our solar system fly from interplanetary spaces - comets, or tailed stars(translated from Greek). The sudden appearance of a comet has always frightened the ignorant man.

They said that devastating bloody wars would begin, troubles, hunger, pestilence would go everywhere, and even the end of the world would come.

Much more often can be observed, especially at the end of summer, august star shower. In the old days, it was believed that every person has his own star in the sky, and when he dies, his star also fades, falls.
The stars certainly don't fall. These are fragments of celestial bodies and disintegrated comets: they heat up to several thousand degrees and begin to glow when they enter the earth's atmosphere.

meteorites

The hot air around the falling bodies also glows. In the event that they do not completely burn out, turning into a hot gas, they fall to the ground heavenly stones, as they used to be called, or meteorites. Sometimes they reach enormous sizes.

The meteorite, which fell in February 1947 in the area of ​​the Sikhote-Alin ridge with a rain of fragments, is believed to have weighed up to one hundred tons. At the site of its fall, I found many deep craters up to 30 meters in diameter. For two years, about 23 tons of meteorite fragments were collected in this area.

Famous Tunguska meteorite, which fell in the summer of 1908 in the remote taiga, near the small village of Vinovara near the river. Podkamennaya Tunguska (Krasnoyarsk Territory), has not yet been found, despite many years of searching. Scientists believe that it exploded on impact and completely disintegrated into tiny particles metal dust.

It was indeed discovered during the analysis of the soil in the area of ​​​​the explosion, which was heard for 1000 kilometers. The explosion column rose to a height of at least 20 kilometers and was visible for 750 kilometers in a circle. On a huge area - up to 60 kilometers in diameter - trees were felled, their tops in all directions from the explosion site.

Scientists believe that about 10 tons of meteorite material falls on Earth every day.

Usually, among the dimly twinkling stars, one can distinguish brighter ones - bluish-white, yellow, reddish. Most stars in a wide silver band - Milky Way, which, like a giant hoop, encircles the vault of heaven.

With his penetrating gaze, man penetrated the innermost depths of the universe and finally saw, through powerful telescopes, distant worlds like the Milky Way. It is not difficult to conclude from this what a modest place ours occupies in the universe - infinite in time and space, having neither beginning nor end.

Star - a hot self-luminous ball

On strict astronomical accounting - millions. The stars and planets of the Universe, as they say, are individually counted, entered into special lists, into a catalog, marked on special maps.
Each star - a hot self-luminous ball similar to our sun.

The stars are very far from us. To the nearest star, that's what it's called Proxima, i.e., in Latin, the nearest, - it would take a very, very long time to get even with the help of a rocket. The light from this star to Earth takes four years, according to astronomers.

The speed of light is very high, 300,000 kilometers per second! From this we can draw the following conclusion, if, say, Proxima will fade today, people will observe its last ray in the sky for four whole years.

One hundred and fifty million kilometers separating from, light travels in 8 minutes 18 seconds. How close to us is the Sun compared to its closest neighbor!

The size of the stars is very different. The giant star (from the constellation Cepheus) is 2300 times larger than the Sun, and the baby stars (the Kuiper star) are almost half the size of the Earth.

The temperature of the stars

different and temperature of the stars. The bluish-white stars are the hottest: their surface temperature is 30,000°; on yellow stars it is already cooler - 6000°, and on red stars 3000° and below. Our Sun is a rather weak star, yellow dwarf as astronomers call it.

The birth of the stars

Exploring the heavenly bodies, scientists have made many interesting conclusions about the birth of stars, about their development and chemical composition. The chemical composition of celestial bodies is studied by a special device - a spectroscope. It makes it possible to detect even negligibly small amounts of a substance by the characteristic colored lines of the spectrum.

Spectrum

Spectrum(from the Latin "spectrum") - visible, vision.
An idea of ​​the spectrum can be obtained from the rainbow after the rain. It attracts with subtle transitions from one color to another: from red - through orange, yellow, green, blue and blue - to purple.

You will never forget the place of each color in the spectrum if you remember this little fable:

Every hunter wants to know where the pheasant is sitting.

Here, the initial letter of the word stands for color.

When a ray of light passes through a trihedral glass prism and falls on a piece of paper or white wall, it also turns out a beautiful rainbow stripe. You will see the same colored stripe on the ceiling or wall if a ray of the sun falls on the edge face of the mirror or the light sparkles with color tints on the faceted balls and pendants of the theatrical chandelier.

Hot solid and liquid bodies, as well as gases under high pressure, form continuous spectra in the form of iridescent stripes, while rarefied gases give, when heated, not a continuous, but a linear spectrum; it consists of separate colored lines characteristic of each substance, separated by dark gaps.

The adaptation of the spectroscope to the telescope made it possible to obtain photographs of the spectra of very distant celestial bodies and draw the conclusion from this that not a single chemical element unknown on Earth has yet been found on them. The same results were given by the chemical analysis of meteorites. Spectral analysis distant stellar worlds and the chemical analysis of meteorites speak convincingly of unity of matter in the universe.

None of the large number of different models of origin and development solar system did not receive a transfer to the rank of a generally accepted theory.

According to Kant-Laplace hypothesis the system of planets around the Sun was formed as a result of the action of forces of attraction and repulsion between particles of scattered matter located in rotary motion around the sun.

First English physicist and astrophysicist J. H. Jeans(1877 - 1946) suggested that once the Sun collided with another star, as a result of which a jet of gas was torn out of it, which, thickening, turned into planets. Given the huge distance between the stars, such a collision seems incredible.

Of the modern hypotheses of the origin of the solar system, the most famous is the electromagnetic hypothesis of the Swedish astrophysicist H. Alfvena (1908 - 1995)and English F. Hoyle (1915 - 2001). According to this theory, the original gas cloud from which both the Sun and the planets were formed consisted of ionized gas subject to the influence of electromagnetic forces. After the Sun was formed from a huge gas cloud through concentration, small parts of this cloud remained at a very large distance from it. The gravitational force began to attract the remaining gas to the formed star - the Sun, but its magnetic field stopped the moving gas at various distances - just where the planets are. Gravitational and magnetic forces influenced the concentration and thickening of this gas. As a result, planets were formed. When the largest planets arose, the same process was repeated on a smaller scale, thus creating systems of satellites.

Also known is the hypothesis of the formation of the solar system from a cold gas and dust cloud surrounding the Sun, proposed by a Soviet scientist. O.Yu. Schmidt (1891 - 1956).

According to the currently accepted hypothesis, the formation of the solar system began about 4.6 billion years ago with the gravitational collapse of a small part of a giant interstellar gas and dust cloud. This initial cloud was probably light-years across and was the parent of several stars.

In the process of gravitational compression, the size of the gas and dust cloud decreased and, due to the law of conservation of angular momentum, the speed of rotation of the cloud increased. The center, where most of the mass had gathered, became hotter and hotter than the surrounding disk. Due to the rotation, the compression rates of the clouds differed parallel and perpendicular to the rotation axis, which led to the flattening of the cloud and the formation of a characteristic protoplanetary disk with a diameter of approximately 200 AU. and a hot, dense protostar at the center. The Sun is thought to have been a T Tauri star at this point in its evolution. The study of such stars shows that they are often accompanied by protoplanetary disks with masses of 0.001 - 0.1 solar masses, with the vast majority of the mass of the nebula concentrated directly in the star. The planets were formed by accretion from this disk (Fig. 27).

Within 50 million years, the pressure and density of hydrogen in the center of the protostar became large enough to start thermonuclear reactions. Temperature, reaction rate, pressure and density increased until hydrostatic equilibrium was reached, with thermal energy resisting the force of gravitational contraction. At this stage, the Sun has become a full-fledged main sequence star.

Fig. 27 Evolution of the Sun

The solar system will last until the Sun begins to evolve out of the main sequence of the Hertzsprung-Russell diagram, which shows the relationship between the brightness of stars and their surface temperatures. Hotter stars are more luminous.

The sun burns off its hydrogen fuel, and the energy released tends to be depleted, causing the sun to shrink. This increases the pressure in its bowels and heats the core, thus accelerating the burning of fuel. As a result, the Sun gets brighter by about ten percent every 1.1 billion years.

In about 5 to 6 billion years, the hydrogen in the Sun's core will be completely converted to helium, which will complete the main sequence phase. At this time, the outer layers of the Sun will expand by about 260 times - the Sun will become a red giant. Due to the tremendously increasing surface area, it will be much cooler than when it is on the main sequence (2600 K).

Ultimately, the outer layers of the Sun will be ejected by a powerful explosion into the surrounding space, forming planetary nebula, in the center of which only a small stellar core will remain - a white dwarf, an unusually dense object half the initial mass of the Sun, but the size of the Earth. This nebula will return some of the material that formed the Sun into the interstellar medium.

Theories of the origin of the solar system are hypothetical in nature, and it is impossible to unambiguously resolve the issue of their reliability at the present stage of the development of science. In all existing theories there are inconsistencies and ambiguities.

The lack of a generally accepted version of the origin of the planetary system has its own explanation. First of all, the uniqueness of the object of observation precludes the use comparative analysis and forces us to solve the difficult task of restoring history on the basis of knowledge of the current state of the solar system alone. For example, ideas about the evolution of stars from their birth to death have been obtained through the accumulation and statistical processing of observed data on state of the art many stars of different classes at different stages of development. It is not surprising that astronomy knows much more about the development of stars far from us than about the origin and development of our habitat - the solar system.

Thus, the solar system is a very complex natural formation, combining the diversity of its constituent elements with the highest stability of the system as a whole. With a huge number and variety of elements that make up the system, with the complex relationships that are established between them, the task of determining the mechanism of its formation turns out to be very difficult.

The solar system includes:

· Sun;

· 4 terrestrial planets: Mercury, Venus, Earth, Mars and their satellites;

the belt of minor planets - asteroids, which includes the planet - the dwarf Ceres;

· countless meteorite bodies moving both in swarms and singly.

4 giant planets: Jupiter, Saturn, Uranus, Neptune and their satellites;

hundreds of comets

· centaurs;

· trans-Neptunian objects: the Kuiper belt, which includes 4 dwarf planets: Pluto, Haumea, Makemake, Eris and the scattered disk;

· Remote areas, which include the Oort and Sedna clouds;

border areas.

Sun

The Sun belongs to the ordinary stars of our Galaxy and is a hot gas (plasma) ball of predominantly helium-hydrogen composition, which is diluted with an admixture (about 1%) of the remaining chemical elements, the ratio of which varies from the surface to the core. AT upper layers The sun contains about 90% hydrogen and 10% helium. The nucleus contains only 37% hydrogen. The ratio between hydrogen and helium over time changes in favor of helium, since thermonuclear reactions have been taking place on the Sun for 4.5 billion years, converting hydrogen nuclei into helium nuclei. Every second, about 600 million tons of hydrogen are converted into helium at a temperature of about 15 million 0 C. At the same time, 4.3 million tons are converted into radiant energy (Fig. 28).

All of us quite often hear that scientists have discovered something or someone on such and such a star or on some planet, or simply carried out research and ... and so on. But, few people think why the planets are called planets, and the stars are stars, and what important differences do they have, since one was separated from the other? At the same time, almost every one of us at least once in his life asked himself a rather stupid question: “Is the sun a star or a planet?” Also, almost every person will immediately answer this question that the Sun is, of course, a star, but far from everyone is able to explain why it is a star and not a planet.

A logical question arises: what is the difference between a star and a planet?

The difference between them is simply huge, although at first glance it is not very noticeable.

1. First and foremost, the stars are able to independently emit light and heat, unlike the planets, which are only able to reflect the rays of light falling on them from other luminaries, being essentially dark bodies.

2. Stars have much higher surface temperatures than any known on the planet. this moment planets. The average temperatures of their surfaces range from 2,000 to 40,000 degrees, not to mention the layers located closer to the center of the cosmic body, where temperatures may even reach millions of degrees.

Data from SDO, a device studying the Sun, for three years of work

3. Stars are much larger than even the largest planets in their mass.

4. All planets move in orbits relative to their luminaries, which, in turn, at the same moment remain completely motionless. This is similar to how our Earth revolves around the Sun. Thanks to this, it is possible to observe the different phases of the planets in the same way as the moon.

5. All the planets in their chemical composition are formed from both solid and light particles, in contrast to the stars predominantly consisting only of light elements.

6. Planets often have one or several satellites at once, but the stars never have such "neighbors". But at the same time, the absence of a satellite is, of course, still not a fact that this cosmic body is not a planet.

7. On the surfaces of absolutely all stars, nuclear or thermonuclear reactions are sure to occur, accompanied by explosions. In turn, these reactions are not observed on the surfaces of planets, well, if only in exceptional cases, and then only on nuclear planets and only very, very weak nuclear reactions.

You can definitely say...

Now we can absolutely say that the Sun is a typical star (the so-called G-type yellow dwarf). Because 8 planets revolve around it, forming the solar system with it; it independently emits light and heat - the average surface temperature is 5000-6000 K; consists predominantly of light elements such as hydrogen and helium - almost 99%, and only 1% are solids; thermonuclear reactions are constantly taking place on its surface; and with its size it exceeds several times any planet in the solar system.

Remember how in Chekhov's story "Kashtanka" the owner of the dog says to her: "Against a man, you are the same as a carpenter against a carpenter"? This is how the stars are in relation to the planets.

Stars

star in astronomy, a celestial body is called, in which thermonuclear reactions take place. These are massive glowing gas (plasma) balls. They are formed from a gas-dust environment (mainly from hydrogen and helium) as a result of gravitational compression. In the depths of stars there is a huge temperature - millions of kelvins, thermonuclear reactions of hydrogen conversion into helium occur (°С = K−273.15). On their surface - thousands of kelvins. Stars are called the main bodies of the universe, because they contain the bulk of the luminous matter in nature. Our Sun is a typical star of spectral class G with a temperature of 5000-6000 K. Spectral classes- classification of stars according to their radiation spectrum, primarily according to the temperature of the photosphere. There are 7 classes in total: O, B, A, F, G, K, M. Within the class, stars are divided into subclasses from 0 (hottest) to 9 (coldest). The sun has spectral type G2 and equivalent photosphere temperature 5780 K.
The star closest to the Sun is Proxima Centauri. It is located 4.2 light years (3.9 1013 km) from the center of the solar system.
When we look at the starry sky, then in clear weather naked eye in the sky we can see about 6000 stars, 3000 in each hemisphere. All stars visible from the Earth (including those visible in the most powerful telescopes) are in the local group of galaxies.

local group galaxies- a gravitationally bound group of galaxies, including galaxies Milky Way, the Andromeda Galaxy (M31) and the Triangulum Galaxy (M33) - it is shown in the picture above.
We will not go into detailed characteristics of the classification of stars, we will only say that the whole variety of types of stars is only a reflection of the quantitative characteristics of stars (such as mass and chemical composition) and the evolutionary stage at which the star is currently located.

Main sequence stars

This is the most numerous class of stars. Our Sun also belongs to it. This is the place in the diagram where the star is located most own life. Energy losses due to radiation are compensated for by the energy released during nuclear reactions. There are other types of stars.

brown dwarfs

This is a type of star in which nuclear reactions could never compensate for the energy lost to radiation. Their existence was predicted in the middle of the 20th century, based on ideas about the processes occurring during the formation of stars, and in 2004 a brown dwarf was first discovered. To date, a lot of stars of this type have been discovered. Their spectral type is M - T.

white dwarfs

white dwarfs are compact stars with masses comparable to the mass of the Sun, but with radii ~100 and, accordingly, luminosities ~10,000 times less than the solar one. They are deprived of their own sources of thermonuclear energy. White dwarfs begin their evolution as the exposed degenerate cores of red giants that have shed their shell - that is, as the central stars of young planetary nebulae. The temperatures of the photospheres of the cores of young planetary nebulae are extremely high. Large stars (7-10 times heavier than the Sun) at some point “burn” hydrogen, helium and carbon and turn into white dwarfs with an oxygen-rich core. The surface temperature of young white dwarfs - isotropic stellar cores after shell ejection is very high - more than 2105 K, however, it drops quite quickly due to neutrino cooling and radiation from the surface.

red giants

Red giants and supergiants- stars of late spectral types with high luminosity and extended shells. Stars in the course of their evolution can reach late spectral classes and high luminosities at two stages of their development: at the stage of star formation and late stages of evolution. The stage at which young stars are observed as red giants depends on their mass - this stage lasts from ~ 103 to ~ 108 years. At this time, the radiation of the star occurs due to the gravitational energy released during compression. With compression, the surface temperature of such stars increases, but, due to a decrease in the size and area of ​​the radiating surface, the luminosity decreases. Ultimately, a reaction starts in their nuclei thermonuclear fusion helium from hydrogen, and the young star enters the main sequence. At the later stages of stellar evolution, after the hydrogen burns out in their interiors, the stars descend from the main sequence and move into the region of red giants and supergiants. Both "young" and "old" red giants have similar characteristics due to the similarity of their internal structure - they all have a hot dense core and a very sparse and extended shell.

The sun is a red giant

The Sun is currently a middle-aged star, estimated to be about 4.57 billion years old. The Sun will remain on the Main Sequence for about 5 billion more years, gradually increasing its brightness by 10% every billion years, after which the hydrogen in the core will be depleted. After that, the temperature and density in the solar core will increase so much that helium combustion will begin, and helium will begin to turn into carbon. The size of the Sun will increase by about 200 times, that is, almost to the modern earth's orbit. Mercury and Venus will be engulfed by it and evaporate completely. The earth, if it does not share their fate, will be heated so much that there will be no chance of saving life. The oceans will evaporate long before the Sun transitions to the red giant stage, in about 1.1 billion years.
At the stage of a red giant, the Sun will be approximately 100 million years, after which it will turn into a planetary nebula, and then become a white dwarf.

variable stars

variable star- a star, the brightness of which changes with time as a result of physical processes occurring in its region. Strictly speaking, the brightness of any star changes with time to one degree or another. To classify a star as a variable, it is sufficient that the brightness of the star undergo a change at least once.
Variable stars are very different from each other. Changes in brightness may be periodic. The main observational characteristics are the period, the amplitude of the brightness changes, the shape of the light curve and the radial velocity curve.
Note: do not confuse the variability of stars with their twinkling, which occurs due to air vibrations earth's atmosphere. Stars do not twinkle when viewed from space.

Wolf-Rayet stars

Wolf-Rayet Stars- a class of stars that are characterized by very high temperature and luminosity; Wolf-Rayet stars differ from other hot stars by the presence in the spectrum of broad emission bands of hydrogen, helium, as well as oxygen, carbon, and nitrogen.

T Tauri stars (T Tauri, T Tauri stars, TTS)- a class of variable stars, named after its prototype T Taurus. They can usually be found near molecular clouds and identified by their variability. The main source of their energy is gravitational compression. The spectrum of T Tauri stars contains lithium, which is absent from the spectra of the Sun and other main sequence stars, as it is destroyed at temperatures above 2,500,000 K.

new stars

new called stars whose luminosity suddenly increases by a factor of ~103-106. All new stars are close binary systems consisting of a white dwarf and a companion star that is on the main sequence or has reached the stage of a red giant in the course of evolution. In such systems, the matter of the outer layers of the companion star flows onto the white dwarf. The composition of the gas falling on the white dwarf is typical of the outer layers of red giants and main sequence stars - more than 90% hydrogen. As hydrogen accumulates in the surface layer and the temperature rises, thermonuclear reactions begin to take place in the hydrogen-rich layer, this is facilitated by the penetration of carbon from the underlying layers of the white dwarf into the degenerate surface layer. Shortly after the flare, a new cycle and accumulation of the hydrogen layer begins, and after a while the flare is repeated. The interval between outbursts ranges from tens of years for repeated novae to thousands of years for classical novae.
New stars are used as distance indicators. Determining the distances of galaxies and clusters of galaxies using novae gives the same accuracy as when using Cepheids.

supernovae

supernovae- these are stars, the brightness of which during a flash increases by tens of magnitudes within a few days. At maximum brightness, a supernova is comparable in brightness to the entire galaxy in which it erupted, and can even exceed it. The term "supernovae" was used to refer to stars that flared up much stronger than the so-called "new stars". In fact, neither one nor the other are physically new: already existing stars flare up. But in several historical cases, those stars that were previously almost or completely invisible in the sky flared up, this phenomenon created the effect of the appearance of a new star.

Other types of stars

Hypernova This is a very large supernova. bright blue variables- very bright blue pulsating hypergiants. Ultra-bright X-ray sources- a celestial body with strong X-ray radiation. neutron stars- an astronomical object, which is one of the end products of the evolution of stars, consisting of a neutron core and a relatively thin (∼1 km) crust of degenerate matter containing heavy atomic nuclei. The mass of a neutron star is almost the same as that of the Sun, but the radius is about 10 km. Therefore, the average density of the matter of such a star is several times higher than the density of the atomic nucleus. It is believed that neutron stars are born during supernova explosions.

star systems

star systems can be single and multiple: double, triple, etc. If the system includes more than ten stars, then it is customary to call it star cluster. Double (multiple) stars are very common. According to some estimates, more than 70% of the stars in the galaxy are multiples.

double stars

, or dual system- two gravitationally bound stars circulating in closed orbits around a common center of mass. With the help of binary stars, it is possible to find out the masses of stars and build various dependencies. All black hole candidates are in binary systems.

star clusters

star cluster- a group of stars that have a common origin, position in space and direction of movement. Members of such groups are interconnected by mutual attraction. Most of the known clusters are in our galaxy.

globular clusters

globular cluster- a cluster of stars that has a spherical or slightly flattened shape. Their diameter ranges from 20 to 100 parsecs. These are some of the oldest objects in the universe. The typical age of globular clusters is over 10 billion years. Globular clusters are characterized by a high concentration of stars. There are more than 150 globular clusters in the Milky Way, most of which are concentrated towards the center of the galaxy.

open clusters

open cluster- the second class of star clusters. This is a star system, the components of which are located at a sufficiently large distance from each other. In this it differs from globular clusters, where the concentration of stars is relatively high. For this reason, open clusters are very difficult to detect and study. If stars at the same distance from the observer move in the same direction, there is reason to believe that they are part of an open cluster.
The most famous representatives of this class of clusters are Pleiades and Hyades located in the constellation Taurus.

star associations

Star associations- a rarefied cluster of young stars of high luminosity, which differs from other types of clusters in its size. Associations, like open clusters, are unstable. They slowly expand and their components move away from each other.

galaxies

Galaxy is a large collection of stars, interstellar gas and dust, dark matter (a form of matter that does not emit electromagnetic radiation and does not interact with it. This property of this form of matter makes it impossible to directly observe it. However, it is possible to detect the presence of dark matter from the gravitational effects it creates).

How are stars born?

At first, it is a cold rarefied cloud of interstellar gas, which is compressed under the influence of its own gravity. In this case, the gravitational energy is converted into heat. When the temperature in the core reaches several million Kelvin, nucleosynthesis reactions begin (the process of formation of nuclei of chemical elements heavier than hydrogen), and the compression stops. In this state, the star stays for most of its life, being on the main sequence of the Hertzsprung-Russell diagram, until the fuel reserves in its core run out. When all the hydrogen in the center of the star turns into helium, the thermonuclear combustion of hydrogen continues on the periphery of the helium core.
During this period, the structure of the star begins to noticeably change. Its luminosity grows, the outer layers expand, while the inner ones, on the contrary, shrink. And for the time being, the brightness of the star also decreases. The surface temperature decreases - the star becomes a red giant. In this state, the star spends much less time than on the main sequence. When the mass of its isothermal helium core becomes significant, it cannot support its own weight and begins to shrink; the temperature rising at the same time stimulates the thermonuclear conversion of helium into heavier elements.
The most massive stars live for a relatively short time - a few million years. The fact of the existence of such stars means that the processes of star formation did not end billions of years ago, but take place in the present era.
Stars, whose mass is many times greater than the mass of the Sun, have huge sizes, high luminosity and temperature for most of their lives. Due to their high temperature, they have a bluish color, and therefore they are called blue supergiants. Most blue supergiants are observed in the region of the Milky Way, i.e., near the plane of the Galaxy, where the concentration of gas and dust interstellar matter is especially high.
Near the plane of the Galaxy, young stars are unevenly distributed. They almost never meet alone. Most often, these stars form open clusters and more rarefied stellar groups of large sizes, called stellar associations, which include tens and sometimes hundreds of blue supergiants. The youngest of the star clusters and associations are less than 10 million years old. In almost all cases, these young formations are observed in regions of increased interstellar gas density. This indicates that the process of star formation is associated with interstellar gas.
An example of a star-forming region is the giant gas complex in the constellation Orion. It occupies almost the entire area of ​​this constellation in the sky and includes a large mass of neutral and molecular gas, dust, and a number of bright gaseous nebulae. The formation of stars in it continues at the present time.

planets

Planet(translated from ancient Greek as “wanderer”) is a celestial body orbiting a star or its remnants, massive enough to become rounded under the influence of its own gravity, but not massive enough to start a thermonuclear reaction, and managed to clear the vicinity of its orbit from planetesimals (a celestial body in orbit around a protostar, formed as a result of the gradual increment of smaller bodies, consisting of dust particles of a protoplanetary disk. Continuously attracting new material and accumulating mass, planetesimals form a larger body, while under the influence of gravity, the individual fragments that compose it begin to condense). There are enough articles about the planets of our solar system on our website in the section “About the planets of the solar system”: http://site/index.php/earth/glubini-vselennoy/15-o-planetah.

But there are planets outside the solar system, they are called exoplanets. Exoplanet or extrasolar planet- a planet orbiting a star outside the solar system. The planets are extremely small and dim compared to the stars, and the stars themselves are far from the Sun (the nearest one is at a distance of 4.22 light years). Therefore, for a long time the task of detecting planets near other stars was unsolvable, the first exoplanets were discovered in the late 1980s. Now such planets began to be discovered thanks to improved scientific methods. Currently, the existence of 843 exoplanets in 665 planetary systems has been reliably confirmed, of which 126 have more than one planet. The total number of exoplanets in the Milky Way galaxy, according to new data, is from 100 billion, of which ~ 5 to 20 billion are possibly "Earth-like". About 34 percent of sun-like stars have planets comparable to Earth in the habitable zone.
Planemo- this is a celestial body, whose mass allows it to fall into the range of definition of a planet, that is, its mass is greater than that of small bodies, but insufficient to start a thermonuclear reaction in the image and likeness of a brown dwarf or star.

So All planets revolve around stars. In the solar system, all the planets revolve in their orbits in the direction in which the sun rotates (counterclockwise when viewed from the north pole of the sun).
In addition to the fact that the planets revolve in their orbit around the star, they also rotate around their axis. The period of rotation of the planet around its axis is known as a day. Most of the planets in the solar system rotate on their axis in the same direction as they orbit the sun, counterclockwise when viewed from the north pole of the sun, except for Venus, which rotates clockwise, and Uranus, whose extreme axial tilt generates controversy, which pole is considered south and which north, and whether it rotates counterclockwise or clockwise. However, whatever opinion the parties hold, the rotation of Uranus is retrograde relative to its orbit.
One of the criteria that allows us to define a celestial body as a classical planet is orbital neighborhoods that are clean from other objects. A planet that has cleared its surroundings has accumulated enough mass to collect or, conversely, disperse all the planetesimals in its orbit. That is, the planet orbits its star in isolation (except for its satellites and Trojans), as opposed to sharing its orbit with many objects of similar size. This criterion for planetary status was proposed by the IAU in August 2006. This criterion deprives such bodies of the solar system as Pluto, Eris and Ceres of the status of a classical planet, classifying them as dwarf planets. Despite the fact that this criterion applies so far only to the planets of the solar system, a number of young star systems that are at the stage of a protoplanetary disk have signs of “clean orbits” for protoplanets.