Everyone knows what the stars look like in the sky. Tiny, glowing lights. In ancient times, people could not come up with an explanation for this phenomenon. The stars were considered the eyes of the gods, the souls of deceased ancestors, guardians and protectors, protecting the peace of man in the darkness of the night. Then no one could have thought that the Sun is also a star.

What is a star

Many centuries passed before people understood what the stars were. Types of stars, their characteristics, ideas about the chemical and physical processes taking place there - this is a new area of ​​\u200b\u200bknowledge. Ancient astronomers could not even imagine that such a luminary was actually not a tiny light at all, but an unimaginable ball of hot gas in which reactions take place

thermonuclear fusion. There is a strange paradox in that dim starlight is the dazzling radiance of a nuclear reaction, and the cozy warmth of the sun is the monstrous heat of millions of kelvins.

All the stars that can be seen in the sky with the naked eye are in the galaxy Milky Way. The sun is also a part of this, and it is located on its outskirts. It is impossible to imagine what the night sky would look like if the Sun were at the center of the Milky Way. After all, the number of stars in this galaxy is more than 200 billion.

A bit about the history of astronomy

Ancient astronomers could also tell unusual and interesting things about the stars in the sky. Already the Sumerians singled out individual constellations and the zodiac circle, they were the first to calculate the division of the full angle by 360 0. They also created the lunar calendar and were able to synchronize it with the solar one. The Egyptians believed that the Earth is in but they knew that Mercury and Venus revolve around the Sun.

In China, astronomy as a science was already practiced at the end of the 3rd millennium BC. e., a

The first observatories appeared in the 12th century. BC e. They studied the moon and solar eclipses, while being able to understand their cause and even calculating the forecast dates, they observed meteor showers and comet trajectories.

The ancient Incas knew the differences between stars and planets. There is indirect evidence that they were aware of the Galileans and the visual blurring of the outlines of the disk of Venus, due to the presence of an atmosphere on the planet.

The ancient Greeks were able to prove the sphericity of the Earth, put forward an assumption about the heliocentricity of the system. They tried to calculate the diameter of the Sun, albeit erroneously. But the Greeks were the first to suggest in principle that the Sun more earth, before that everyone, relying on visual observations, believed otherwise. The Greek Hipparchus was the first to create a catalog of luminaries and single out different types stars. The classification of stars in this scientific work based on light intensity. Hipparchus singled out 6 classes of brightness, in total there were 850 luminaries in the catalog.

What did ancient astronomers pay attention to?

The original classification of stars was based on their brightness. After all, this criterion is the only one available to an astronomer armed only with a telescope. The brightest stars or those with unique visible properties even received their own names, and each nation has its own. So, Deneb, Rigel and Algol are Arabic names, Sirius is Latin, and Antares is Greek. The polar star in every nation has its own name. This is perhaps one of the most important in the "practical sense" of the stars. Its coordinates in the night sky are unchanged, despite the rotation of the earth. If the rest of the stars move across the sky, going from sunrise to sunset, then the North Star does not change its location. Therefore, it was she who was used by sailors and travelers as a reliable guide. By the way, contrary to popular belief, this is not the brightest star in the sky. The polar star does not stand out in any way - neither in size nor in intensity of luminescence. You can only find it if you know where to look. It is located at the very end of the "ladle handle" Ursa Minor.

What is the star classification based on?

Modern astronomers, answering the question of what types of stars are, are unlikely to mention the brightness of the glow or the location in the night sky. Unless in the order of a historical digression or in a lecture designed for an audience that is very far from astronomy.

The modern classification of stars is based on their spectral analysis. In this case, the mass, luminosity and radius of the celestial body are usually also indicated. All these indicators are given in relation to the Sun, that is, it is its characteristics that are taken as units of measurement.

The classification of stars is based on such a criterion as absolute magnitude. This is the apparent degree of brightness without the atmosphere, conventionally located at a distance of 10 parsecs from the point of observation.

In addition, the brightness variability and the size of the star are taken into account. The types of stars are currently determined by their spectral class and, in more detail, by their subclass. Astronomers Russell and Hertzsprung independently analyzed the relationship between luminosity, absolute temperature surface and spectral type of luminaries. They built a chart with the corresponding coordinate axes and found that the result was not at all chaotic. The luminaries on the graph were located in clearly distinguishable groups. The diagram allows, knowing the spectral type of a star, to determine its absolute magnitude with at least approximate accuracy.

How stars are born

This diagram provided clear evidence in favor of modern theory data evolution celestial bodies. The graph clearly shows that the most numerous class are those belonging to the so-called main sequence stars. The types of stars belonging to this segment are at the most common development point in the Universe at the moment. This is a stage in the development of the luminary, at which the energy expended on radiation is compensated by the energy received during thermonuclear reaction. The length of stay at this stage of development is determined by the mass of the celestial body and the percentage of elements heavier than helium.

The currently accepted theory of stellar evolution states that at the initial

stage of development, the luminary is a rarefied giant gas cloud. Under the influence of its own gravity, it shrinks, gradually turning into a ball. The stronger the compression, the more intense the gravitational energy is converted into heat. The gas heats up, and when the temperature reaches 15-20 million K, a thermonuclear reaction starts in the newborn star. After that, the process of gravitational contraction is suspended.

The main period of a star's life

At first, the reactions of the hydrogen cycle predominate in the bowels of the young luminary. This is the longest period of a star's life. The types of stars that are at this stage of development are presented in the most massive main sequence of the diagram described above. Over time, the hydrogen in the core of the star ends, turning into helium. After that, thermonuclear combustion is possible only at the periphery of the nucleus. The star becomes brighter, its outer layers expand significantly, and the temperature drops. The celestial body turns into a red giant. This period of a star's life

much shorter than the previous one. Her subsequent fate is little known. There are various assumptions, but reliable confirmation of them has not yet been received. The most common theory says that when there is too much helium, the stellar core, unable to withstand its own mass, shrinks. The temperature rises until the helium already enters into a thermonuclear reaction. Monstrous temperatures lead to another expansion, and the star turns into a red giant. Further fate luminaries, according to scientists, depends on its mass. But theories regarding this are just the result of computer simulations, not confirmed by observations.

cooling stars

Presumably, low-mass red giants will shrink, turning into dwarfs and gradually cooling down. Intermediate-mass stars can transform into, while in the center of such formation, the core devoid of external covers will continue to exist, gradually cooling down and turning into a white dwarf. If the central star emitted significant infrared radiation, conditions arise for the activation of a space maser in the expanding gaseous envelope of the planetary nebula.

Massive luminaries, shrinking, can reach such a level of pressure that electrons are literally pressed into atomic nuclei turning into neutrons. Because between

these particles do not have electrostatic repulsion forces, the star can shrink to a size of several kilometers. At the same time, its density will exceed the density of water by 100 million times. Such a star is called a neutron star and is, in fact, a huge atomic nucleus.

Supermassive stars continue to exist, sequentially synthesizing in the process of thermonuclear reactions from helium - carbon, then oxygen, from it - silicon and, finally, iron. At this stage of the thermonuclear reaction, a supernova explosion occurs. Supernovae, in turn, can turn into neutron stars or, if their mass is large enough, continue to collapse to a critical limit and form black holes.

Dimensions

The classification of stars by size can be realized in two ways. The physical size of a star can be determined by its radius. The unit of measurement in this case is the radius of the Sun. There are dwarfs, medium-sized stars, giants and supergiants. By the way, the Sun itself is just a dwarf. The radius of neutron stars can reach only a few kilometers. And in the supergiant, the entire orbit of the planet Mars will fit. The size of a star can also be understood as its mass. It is closely related to the diameter of the star. The larger the star, the lower its density, and vice versa, the smaller the star, the higher the density. This criterion is not viable so much. There are very few stars that would be 10 times larger or smaller than the Sun. Most of the luminaries fit into the interval from 60 to 0.03 solar masses. The density of the Sun, taken as the starting indicator, is 1.43 g/cm 3 . The density of white dwarfs reaches 10 12 g/cm 3 , while the density of rarefied supergiants can be millions of times less than that of the sun.

In the standard classification of stars, the mass distribution scheme is as follows. The small ones include luminaries with a mass of 0.08 to 0.5 solar. To moderate - from 0.5 to 8 solar masses, and to massive - from 8 or more.

Star classification . From blue to white

The classification of stars by color is actually based not on the visible glow of the body, but on spectral characteristics. The emission spectrum of an object is determined chemical composition stars, its temperature depends on it.

The most common is the Harvard classification, created in the early 20th century. According to the then accepted standards, the classification of stars by color involves the division into 7 types.

So, the stars with the highest temperature, from 30 to 60 thousand K, belong to class O luminaries. They blue color, the mass of such celestial bodies reaches 60 solar masses (cm), and the radius - 15 solar radii (sm). The lines of hydrogen and helium in their spectrum are rather weak. The luminosity of such celestial objects can reach 1 million 400 thousand solar luminosities (s. s.).

Class B stars include luminaries with a temperature of 10 to 30 thousand K. These are celestial bodies of white-blue color, their mass starts from 18 s. m., and the radius - from 7 s. m. The lowest luminosity of objects of this class is 20 thousand s. s., and the hydrogen lines in the spectrum are enhanced, reaching average values.

Class A stars have temperatures ranging from 7.5 to 10 thousand K, they white color. The minimum mass of such celestial bodies starts from 3.1 s. m., and the radius - from 2.1 s. R. The luminosity of objects is in the range from 80 to 20 thousand s. from. The hydrogen lines in the spectrum of these stars are strong, and metal lines appear.

Objects of class F are actually yellow-white, but they look white. Their temperature ranges from 6 to 7.5 thousand K, mass varies from 1.7 to 3.1 cm, radius - from 1.3 to 2.1 s. R. The luminosity of such stars varies from 6 to 80 s. from. The hydrogen lines in the spectrum weaken, the metal lines, on the contrary, increase.

Thus, all types of white stars fall within classes from A to F. Further, according to the classification, yellow and orange luminaries follow.

Yellow, orange and red stars

Types of stars are distributed in color from blue to red, as the temperature decreases and the size and luminosity of the object decreases.

Class G stars, which include the Sun, reach temperatures from 5 to 6 thousand K, they yellow color. The mass of such objects is from 1.1 to 1.7 s. m., radius - from 1.1 to 1.3 s. R. Luminosity - from 1.2 to 6 s. from. The spectral lines of helium and metals are intense, the lines of hydrogen are getting weaker.

Luminaries belonging to class K have a temperature of 3.5 to 5 thousand K. They look yellow-orange, but the true color of these stars is orange. The radius of these objects is in the range from 0.9 to 1.1 s. r., weight - from 0.8 to 1.1 s. m. The brightness ranges from 0.4 to 1.2 s. from. Hydrogen lines are almost imperceptible, metal lines are very strong.

The coldest and smallest stars are of class M. Their temperature is only 2.5 - 3.5 thousand K and they seem to be red, although in reality these objects are orange-red. The mass of stars is in the range from 0.3 to 0.8 s. m., radius - from 0.4 to 0.9 s. R. Luminosity - only 0.04 - 0.4 s. from. These are dying stars. Only recently discovered brown dwarfs are colder than them. A separate class M-T was allocated for them.

The stars that we observe vary both in color and brightness. The brightness of a star depends on both its mass and its distance. And the color of the glow depends on the temperature on its surface. The coldest stars are red. And the hottest ones are a bluish tint. White and blue stars- the hottest, their temperature is higher than the temperature of the Sun. Our star the Sun belongs to the class of yellow stars.

How many stars are in the sky?
It is practically impossible to calculate even at least approximately the number of stars in the part of the Universe known to us. Scientists can only say that in our Galaxy, which is called the "Milky Way", there may be about 150 billion stars. But there are other galaxies too! But much more precisely, people know the number of stars that can be seen from the surface of the Earth with the naked eye. There are about 4.5 thousand such stars.

How are stars born?
If the stars are lit, does anyone need it? In the boundless outer space there are always molecules of the simplest substance in the universe - hydrogen. Somewhere there is less hydrogen, somewhere more. Under the action of forces of mutual attraction, hydrogen molecules are attracted to each other. These processes of attraction can last for a very long time - millions and even billions of years. But sooner or later, hydrogen molecules are attracted so close to each other that a gas cloud is formed. With further attraction, the temperature in the center of such a cloud begins to rise. Millions more years will pass, and the temperature in the gas cloud can rise so much that the reaction of thermonuclear fusion will begin - hydrogen will begin to turn into helium and a new star will appear in the sky. Any star is a hot ball of gas.

The lifespan of stars varies greatly. Scientists have found that the greater the mass of a newborn star, the shorter its lifespan. The lifetime of a star can range from hundreds of millions of years to billions of years.

Light year
A light year is the distance that a ray of light travels in a year at a speed of 300,000 kilometers per second. And there are 31536000 seconds in a year! So, from the star closest to us called Proxima Centauri, a beam of light flies for more than four years (4.22 light years)! This star is 270 thousand times farther from us than the Sun. And the rest of the stars are much further away - tens, hundreds, thousands and even millions of light years from us. This is why stars appear so small to us. And even in the most powerful telescope, unlike the planets, they are always visible as points.

What is a "constellation"?
Since ancient times, people have looked at the stars and seen in the bizarre figures that form groups of bright stars, images of animals and mythical heroes. Such figures in the sky began to be called constellations. And, although in the sky the stars included by people in a particular constellation are visually next to each other, in outer space these stars can be at a considerable distance from each other. The most famous constellations are Ursa Major and Ursa Minor. The fact is that in the constellation Ursa Minor enters the North Star, which is indicated by North Pole our planet Earth. And knowing how to find the North Star in the sky, any traveler and navigator will be able to determine where the north is and navigate the terrain.

supernovae
Some stars at the end of their lives suddenly begin to glow thousands and millions of times brighter than usual, and throw huge masses of matter into the surrounding space. It is customary to say that a supernova explosion occurs. The glow of a supernova gradually fades, and in the end, only a luminous cloud remains in the place of such a star. A similar supernova explosion was observed by ancient astronomers of the Near and Far East July 4, 1054. The decay of this supernova lasted 21 months. Now in the place of this star is the Crab Nebula, known to many astronomy lovers.

Summing up this section, we note that

v. Types of stars

The main spectral classification of stars:

brown dwarfs

Brown dwarfs are a type of star in which nuclear reactions could never compensate for energy losses due to radiation. For a long time brown dwarfs were hypothetical objects. Their existence was predicted in the middle of the 20th century, based on ideas about the processes occurring during the formation of stars. However, in 2004, a brown dwarf was first discovered. To date, a lot of stars of this type have been discovered. Their spectral class is M - T. In theory, one more class is distinguished - denoted by Y.

white dwarfs

Shortly after a helium flash, carbon and oxygen "light up"; each of these events causes a strong rearrangement of the star and its rapid movement along the Hertzsprung-Russell diagram. The size of the star's atmosphere increases even more, and it begins to intensively lose gas in the form of expanding stellar wind streams. The fate of the central part of the star depends entirely on its initial mass: the core of the star can end its evolution as white dwarf(low-mass stars), if its mass in the later stages of evolution exceeds the Chandrasekhar limit - as neutron star(pulsar), but if the mass exceeds the limit of Oppenheimer - Volkov - how black hole. In the last two cases, the completion of the evolution of stars is accompanied by catastrophic events - supernova explosions.
The vast majority of stars, including the Sun, end their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a factor of a hundred and the density becomes a million times higher than that of water, the star is called a white dwarf. It is deprived of sources of energy and, gradually cooling down, becomes dark and invisible.

red giants

Red giants and supergiants are stars with a rather low effective temperature (3000 - 5000 K), but with a huge luminosity. Typical absolute magnitude of such objects? 3m-0m(I and III class luminosity). Their spectrum is characterized by the presence of molecular absorption bands, and the emission maximum falls on the infrared range.

variable stars

A variable star is a star whose brightness has changed at least once in the entire history of its observation. There are many reasons for variability and they can be associated not only with internal processes: if the star is double and the line of sight lies or is at a slight angle to the field of view, then one star, passing through the disk of the star, will outshine it, and the brightness can also change if the light from the star passes through a strong gravitational field. However, in most cases, variability is associated with unstable internal processes. IN latest version The general catalog of variable stars has the following division:
Eruptive variable stars- these are stars that change their brightness due to violent processes and flares in their chromospheres and coronas. The change in luminosity is usually due to changes in the envelope or loss of mass in the form of a stellar wind of varying intensity and/or interaction with the interstellar medium.
Pulsating Variable Stars are stars showing periodic expansion and contraction of their surface layers. Pulsations can be radial or non-radial. Radial pulsations of a star leave its shape spherical, while non-radial pulsations cause the star's shape to deviate from spherical, and adjacent zones of the star can be in opposite phases.
Rotating variable stars- these are stars, in which the distribution of brightness over the surface is non-uniform and / or they have a non-ellipsoidal shape, as a result of which, when the stars rotate, the observer fixes their variability. Non-uniformity in surface brightness can be caused by the presence of spots or temperature or chemical inhomogeneities caused by magnetic fields, whose axes do not coincide with the axis of rotation of the star.
Cataclysmic (explosive and nova-like) variable stars. The variability of these stars is caused by explosions, which are caused by explosive processes in their surface layers (novae) or deep in their depths (supernovae).
Eclipsing binary systems.
Optical variable binary systems with hard X-rays
New Variable Types- types of variability discovered during the publication of the catalog and therefore not included in already published classes.

New

A nova is a type of cataclysmic variable. Their brightness does not change as sharply as that of supernovae (although the amplitude can be 9m): a few days before the maximum, the star is only 2m fainter. The number of such days determines which class of novae a star belongs to:
Very fast if this time (referred to as t2) is less than 10 days.
Quick - 11 Very slow: 151 Extremely slow, being near the maximum for years.

There is a dependence of the maximum brightness of the nova on t2. Sometimes this relationship is used to determine the distance to a star. The flare maximum behaves differently in different ranges: when a decrease in radiation is already observed in the visible range, an increase still continues in the ultraviolet. If a flash is also observed in the infrared range, then the maximum will be reached only after the brightness in the ultraviolet begins to decline. Thus, the bolometric luminosity during a flare remains unchanged for quite a long time.

In our Galaxy, two groups of novae can be distinguished: new disks (on average they are brighter and faster), and new bulges, which are slightly slower and, accordingly, slightly weaker.

supernovae

Supernovae are stars that end their evolution in a catastrophic explosive process. The term "supernovae" was used to refer to stars that flared up much (by orders of magnitude) stronger than the so-called "new stars". In fact, neither one nor the other is physically new, already existing stars always flare up. But in several historical cases, those stars that were previously almost or completely invisible in the sky flared up, which created the effect of the appearance of a new star. The type of supernova is determined by the presence of hydrogen lines in the flare spectrum. If it is, then a type II supernova, if not, then a type I

Hypernovae

Hypernova - the collapse of an exceptionally heavy star after it no longer has sources to support thermonuclear reactions; in other words, it is a very large supernova. Since the beginning of the 1990s, such powerful explosions of stars have been observed that the force of the explosion exceeded the power of the explosion of an ordinary supernova by about 100 times, and the energy of the explosion exceeded 1046 joules. In addition, many of these explosions were accompanied by very strong gamma-ray bursts. Intensive survey of the sky has found several arguments in favor of the existence of hypernovae, but so far, hypernovae are hypothetical objects. Today, the term is used to describe the explosions of stars with masses from 100 to 150 or more solar masses. Hypernovae could theoretically pose a serious threat to the Earth due to a strong radioactive flare, but at present there are no stars near the Earth that could pose such a danger. According to some reports, 440 million years ago there was an explosion of a hypernova near the Earth. Probably, the short-lived isotope of nickel 56Ni hit the Earth as a result of this explosion.

neutron stars

In stars more massive than the Sun, the pressure of degenerate electrons cannot hold back the collapse of the core, and it continues until most of the particles turn into neutrons packed so tightly that the size of the star is measured in kilometers and the density is 280 trillion. times the density of water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.

Everyone knows three states of matter - solid, liquid and gaseous.. What happens to a substance when it is sequentially heated to high temperatures in a closed volume? - Sequential transition from one state of aggregation to another: solid - liquid - gas(due to the increase in the speed of movement of molecules with increasing temperature). With further heating of the gas at temperatures above 1,200 ºС, the disintegration of gas molecules into atoms begins, and at temperatures above 10,000 ºС, partial or complete disintegration of gas atoms into their constituent elementary particles - electrons and atomic nuclei. Plasma is the fourth state of matter, in which the molecules or atoms of matter are partially or completely destroyed by high temperatures or for other reasons. 99.9% of the matter in the Universe is in the state of plasma.

Stars are a class of cosmic bodies with a mass of 10 26 -10 29 kg. A star is a hot plasma spherical cosmic body, which is, as a rule, in hydrodynamic and thermodynamic equilibrium.

If the equilibrium is disturbed, the star begins to pulsate (its dimensions, luminosity and temperature change). The star becomes a variable star.

variable star is a star whose brilliance (apparent brightness in the sky) changes over time. The reasons for the variability can be physical processes in the interior of the star. Such stars are called physical variables(for example, δ Cephei. Variable stars similar to it began to be called Cepheids).

meet and eclipse variables stars whose variability is caused by mutual eclipses of their components(for example, β Perseus - Algol. Its variability was first discovered in 1669 by the Italian economist and astronomer Geminiano Montanari).

Eclipsing variable stars are always double, those. composed of two closely spaced stars. Variable stars on star charts are indicated by a circled circle:

Stars are not always balls. If the star rotates very quickly, then its shape is not spherical. The star shrinks from the poles and becomes like a tangerine or a pumpkin (for example, Vega, Regulus). If the star is double, then the mutual attraction of these stars to each other also affects their shape. They become ovoid or melon-shaped (for example, components of the binary star β Lyra or Spica):

Stars are the main inhabitants of our Galaxy (our Galaxy is written with a capital letter). It contains about 200 billion stars. With the help of even the largest telescopes, only half a percent of the total number of stars in the Galaxy can be seen. More than 95% of all matter observed in nature is concentrated in stars. The remaining 5% are interstellar gas, dust, and all non-luminous bodies.

Apart from the Sun, all the stars are so far from us that even in the largest telescopes they are observed in the form of luminous points of different colors and brilliance. The closest to the Sun is the α Centauri system, which consists of three stars. One of them - a red dwarf called Proxima - is the closest star. It is 4.2 light years away. To Sirius - 8.6 St. years, to Altair - 17 St. years. To Vega - 26 St. years. To the North Star - 830 St. years. To Deneb - 1,500 St. years. For the first time, the distance to another star (it was Vega) in 1837 was able to determine V.Ya. Struve.

The first star that managed to get an image of the disk (and even some spots on it) is Betelgeuse (α Orion). But this is because Betelgeuse is 500-800 times larger than the Sun in diameter (the star is pulsating). An image of the disk of Altair (α Eagle) was also obtained, but this is because Altair is one of the nearest stars.

The color of stars depends on the temperature of their outer layers. Temperature range - from 2000 to 60000 °C. The coldest stars are red and the hottest are blue. By the color of the star, you can judge how hot its outer layers are.

Examples of red stars: Antares (α Scorpio) and Betelgeuse (α Orion).

Examples of orange stars: Aldebaran (α Taurus), Arcturus (α Bootes) and Pollux (β Gemini).

Examples of yellow stars: Sun, Capella (α Aurigae) and Toliman (α Centauri).

Examples of yellowish-white stars are Procyon (α Minor Canis) and Canopus (α Carinae).

Examples of white stars are Sirius (α Canis Major), Vega (α Lyrae), Altair (α Eagle) and Deneb (α Cygnus).

Examples of bluish stars: Regulus (α Leo) and Spica (α Virgo).

Due to the fact that very little light comes from the stars, the human eye is able to distinguish color shades only in the brightest of them. Through binoculars and even more so through a telescope (they capture more light than the eye), the color of the stars becomes more noticeable.

Temperature increases with depth. Even the coldest stars in the center reach millions of degrees. The Sun has about 15,000,000 ° C in the center (they also use the Kelvin scale - the scale of absolute temperatures, but when it comes to very high temperatures, the difference of 273 º between the Kelvin and Celsius scales can be neglected).

What is it that heats up the stellar interior so much? It turns out that there are thermonuclear processes, resulting in a huge amount of energy being released. In Greek, "thermos" means warm. The main chemical element that stars are made of is hydrogen. It is he who is the fuel for thermonuclear processes. In these processes, the nuclei of hydrogen atoms are converted into the nuclei of helium atoms, which is accompanied by the release of energy. The number of hydrogen nuclei in the star decreases, while the number of helium nuclei increases. Over time, other chemical elements are synthesized in the star. All the chemical elements that make up the molecules of various substances were once born in the depths of stars."Stars are the past of man, and man is the future of the star," - this is sometimes figuratively said.

The process by which a star emits energy in the form of electromagnetic waves and particles is called radiation. Stars radiate energy not only in the form of light and heat, but also other types of radiation - gamma rays, X-rays, ultraviolet, radio radiation. In addition, stars emit streams of neutral and charged particles. These streams form the stellar wind. Stellar wind is the process of outflow of matter from stars into outer space. As a result, the mass of stars is constantly and gradually decreasing. It is the stellar wind from the Sun (solar wind) that leads to the appearance of auroras on Earth and other planets. It is the solar wind that deflects the tails of comets away from the Sun.

Stars, of course, do not appear from emptiness (the space between stars is not an absolute vacuum). The material is gas and dust. They are unevenly distributed in space, forming shapeless clouds of very low density and enormous extent - from one or two to tens of light years. Such clouds are called diffuse gas and dust nebulae. The temperature in them is very low - about -250 °C. But not every gas-dust nebula produces stars. Some nebulae can exist for a long time without stars. What conditions are necessary for the start of the process of the birth of stars? The first is the mass of the cloud. If there is not enough matter, then, of course, the star will not appear. Second, compactness. In a cloud that is too extended and loose, the processes of its compression cannot begin. Well, and thirdly, we need a seed - i.e. a bunch of dust and gas, which will later become the embryo of a star - a protostar. protostar is a star at the final stage of its formation. If these conditions are met, then gravitational compression and heating of the cloud begins. This process ends star formation- the emergence of new stars. This process takes millions of years. Astronomers have found nebulae in which the process of star formation is in full swing - some stars have already lit up, some are in the form of embryos - protostars, and the nebula is still preserved. An example is the Great Nebula of Orion.

The main physical characteristics of a star are luminosity, mass and radius.(or diameter), which are determined from observations. Knowing them, as well as the chemical composition of the star (which is determined by its spectrum), it is possible to calculate the model of the star, i.e. physical conditions in its depths, to explore the processes that take place in it.Let us dwell in more detail on the main characteristics of stars.

Weight. The mass can be directly estimated only by the gravitational effect of the star on the surrounding bodies. The mass of the Sun, for example, was determined from the known periods of revolution of the planets around it. Other stars do not directly observe planets. Reliable measurement of mass is possible only for binary stars (in this case, Kepler's law generalized by Newton III is used, no and then the error is 20-60%). Approximately half of all stars in our galaxy are binary. The masses of stars range from ≈0.08 to ≈100 solar masses.Stars with a mass less than 0.08 of the mass of the Sun do not exist, they simply do not become stars, but remain dark bodies.Stars with a mass greater than 100 solar masses are extremely rare. Most stars have masses less than 5 solar masses. The fate of the star depends on the mass, i.e. the scenario according to which the star develops, evolves. Small cold red dwarfs use hydrogen very economically and therefore their life spans hundreds of billions of years. The life span of the Sun - a yellow dwarf - is about 10 billion years (the Sun has already lived about half of its life). Massive supergiants consume hydrogen quickly and die out within a few million years after their birth. The more massive the star, the shorter its life path.

The age of the universe is estimated at 13.7 billion years. Therefore, stars older than 13.7 billion years do not yet exist.

• Stars with mass 0,08 the masses of the Sun are brown dwarfs; their fate is constant contraction and cooling with the cessation of all thermonuclear reactions and transformation into dark planet-like bodies.

• Stars with mass 0,08-0,5 the masses of the Sun (these are always red dwarfs) after the consumption of hydrogen begin to slowly shrink, while heating up and becoming a white dwarf.
  

• Stars with mass 0,5-8 masses of the Sun at the end of life turn first into red giants, and then into white dwarfs. In this case, the outer layers of the star are scattered in outer space in the form planetary nebula. A planetary nebula is often spherical or ring shaped.
  

• Stars with mass 8-10 solar masses can explode at the end of their lives, or they can age quietly, first turning into red supergiants, and then into red dwarfs.

• Stars with a mass greater than 10 masses of the Sun at the end of their life path, they first become red supergiants, then explode as supernovae (a supernova is not a new, but an old star) and then turn into neutron stars or become black holes.
  

Black holes- these are not holes in outer space, but objects (remnants of massive stars) with a very large mass and density. Black holes do not possess any supernatural or magical powers, they are not "monsters of the Universe". They just have such a strong gravitational field that no radiation (neither visible - light, nor invisible) can leave them. Therefore, black holes are not visible. However, they can be detected by their effect on the surrounding stars, nebulae. Black holes are a completely common phenomenon in the Universe and you should not be afraid of them. There may be a supermassive black hole at the center of our galaxy.

Radius (or diameter). The sizes of stars vary widely - from a few kilometers (neutron stars) to 2,000 solar diameters (supergiants). As a rule, the smaller the star, the higher its average density. In neutron stars, the density reaches 10 13 g / cm 3! A thimble of such a substance would weigh 10 million tons on Earth. But in supergiants, the density is less than the density of air near the surface of the Earth.

The diameters of some stars compared to the Sun:

Sirius and Altair are 1.7 times larger,

Vega is 2.5 times larger,

Regulus 3.5 times more

Arcturus is 26 times bigger

Polar is 30 times larger,

Rigel is 70 times larger,

Deneb is 200 times more

Antares is 800 times bigger

YV Canis Major is 2,000 times larger (the largest known star).

Luminosity is the total energy emitted by an object (in this case, stars) per unit of time. The luminosity of stars is usually compared with the luminosity of the Sun (the luminosity of stars is expressed in terms of the luminosity of the Sun). Sirius, for example, radiates 22 times more energy than the Sun (the luminosity of Sirius is 22 Suns). The luminosity of Vega is 50 Suns, and the luminosity of Deneb is 54,000 Suns (Deneb is one of the most powerful stars).

The apparent brightness (more correctly, brilliance) of a star in the earth's sky depends on:

- distance to the star. If a star approaches us, then its apparent brightness will gradually increase. Conversely, as a star moves away from us, its apparent brightness will gradually decrease. If we take two identical stars, then the one closest to us will seem brighter.

- on the temperature of the outer layers. The hotter the star, the more light energy it sends into space, and the brighter it will appear. If a star cools, then its apparent brightness in the sky will decrease. Two stars of the same size and at the same distance from us will appear the same in apparent brightness, provided that they emit the same amount of light energy, i.e. have the same temperature of the outer layers. If one of the stars is colder than the other, then it will appear less bright.

- size (diameter). If we take two stars with the same temperature of the outer layers (of the same color) and place them at the same distance from us, then the larger star will emit more light energy, which means it will appear brighter in the sky.

- from the absorption of light by clouds of cosmic dust and gas that are in the path of the line of sight. The thicker the layer of cosmic dust, the more light from the star it absorbs, and the dimmer the star appears. If we take two identical stars and place a gas-dust nebula in front of one of them, then just this star will appear less bright.

- from the height of the star above the horizon. There is always a dense haze near the horizon, which absorbs some of the light from the stars. Near the horizon (shortly after sunrise or shortly before sunset) the stars always appear dimmer than when they are overhead.

It is very important not to confuse the concepts of "appear" and "be". star may to be very bright in itself, but seem dim due to various reasons: due to the large distance to it, due to its small size, due to the absorption of its light by cosmic dust or dust in the Earth's atmosphere. Therefore, when they talk about the brightness of a star in the earth's sky, they use the phrase "apparent brightness" or "brilliance".

As already mentioned, there are binary stars. But there are also triple (for example, α Centauri), and quadruple (for example, ε Lyra), and five, and six (for example, Castor), etc. The individual stars in a star system are called components. Stars with more than two components are called multiples stars. All components of a multiple star are connected by mutual gravitational forces (form a system of stars) and move along complex trajectories.

If there are many components, then this is no longer a multiple star, but star cluster. Distinguish ball And scattered star clusters. Globular clusters contain many old stars and are older than open clusters, which contain many young stars. Globular clusters are quite stable, because the stars in them are located at small distances from each other and the forces of mutual attraction between them are much greater than between the stars of open clusters. Open clusters dissipate even more over time.

Open clusters, as it is correct, are located in the band of the Milky Way or nearby. On the contrary, globular clusters are located in the starry sky away from the Milky Way.

Some star clusters can be seen in the sky even with the naked eye. For example, open clusters of Hyades and Pleiades (M 45) in Taurus, open clusters of Manger (M 44) in Cancer, globular cluster M 13 in Hercules. Quite a lot of them can be seen with binoculars.

what color are the stars? and why?

1. Stars come in all colors of the rainbow. Because they have different temperatures and composition.

2. 
   
   http://www.pockocmoc.ru/color.php

   
   

3. The stars have a variety of colors. Arcturus has a yellow-orange hue, Rigel is white-blue, Antares is bright red. The dominant color in the spectrum of a star depends on the temperature of its surface. The gas envelope of a star behaves almost like an ideal emitter (an absolutely black body) and completely obeys the classical radiation laws of M. Planck (18581947), J. Stefan (18351893) and V. Wien (18641928), which relate the temperature of the body and the nature of its radiation. Planck's law describes the distribution of energy in the spectrum of a body. He indicates that with increasing temperature, the total radiation flux increases, and the maximum in the spectrum shifts towards short waves. The wavelength (in centimeters), which accounts for the maximum radiation, is determined by Wien's law: lmax = 0.29/T. It is this law that explains the red color of Antares (T = 3500 K) and the bluish color of Rigel (T = 18000 K).

   HARVARD SPECTRAL CLASSIFICATION

   Spectral class Effective temperature, KColor
   O———————————————2600035000 ——————Blue
   B ———————————————1200025000 ———-White-blue
   A ————————————————800011000 ———————White
   F ————————————————-62007900 ———-Yellow white
   G ————————————————50006100 ——————-Yellow
   K ————————————————-35004900 ————-Orange
   M ————————————————26003400 ——————Red

4. Our sun is a pale yellow star. In general, stars have a wide variety of colors and their shades. The differences in the color of the stars are due to the fact that they have different temperatures. And here's why it's happening. Light, as you know, is a wave radiation, the wavelength of which is very small. If, however, even slightly change the length of this light, then the color of the picture that we observe will change dramatically. For example, the wavelength of red is one and a half times the wavelength of blue.

   Cluster of multicolored stars

   Scientists have formulated physical laws that relate color and temperature. The hotter the body, the greater the radiation energy from its surface and the shorter the length of the emitted waves. Therefore, if a body radiates in the blue wavelength range, then it is hotter than a body that radiates red.
   Atoms of hot gases of stars emit photons. The hotter the gas, the higher the photon energy and the shorter their wave. Therefore, the hottest new stars emit in the blue-white range. As their nuclear fuel is used up, the stars cool down. Therefore, old, cooling stars radiate in the red range of the spectrum. Middle-aged stars, such as the Sun, radiate in the yellow range.
   Our Sun is relatively close to us, and therefore we clearly see its color. Other stars are so far away from us that even with the help of powerful telescopes we cannot say with certainty what color they are. To clarify this issue, scientists use a spectrograph - a device for detecting the spectral composition of starlight.

5. Depends on the temperature The hottest white and blue colors are the coldest red ones, but even then they have a temperature higher than any molten metal
6. is the sun white?
7. The perception of color is purely subjective, it depends on the reaction of the retina of the observer's eye.
8. in the sky? I know that there are blue ones, and yellow ones, and white ones. our sun is a yellow dwarf
9. Stars come in different colors. Blue ones have a higher temperature than red ones and more radiation energy from its surface. They also come in white, yellow, and orange, and almost all of them are made of hydrogen.
10. Stars come in a variety of colors, almost all colors of the rainbow (for example: our Sun is yellow, Rigel is white-blue, Antares is red, etc.)

    The differences in the color of the stars are due to the fact that they have different temperatures. And here's why it's happening. Light, as you know, is a wave radiation, the wavelength of which is very small. If, however, even slightly change the length of this light, then the color of the picture that we observe will change dramatically. For example, the wavelength of red is one and a half times the wavelength of blue.

    As you know, as the temperature rises, the heated metal first begins to glow red, then yellow, and finally white. The stars shine the same way. Reds are the coldest, while whites (or even blues!) are the hottest. A newly bursting star will have a color corresponding to the energy released in its core, and the intensity of this release, in turn, depends on the mass of the star. Consequently, all normal stars are the colder the redder they are, so to speak. "Heavy" stars are hot and white, while "light", non-massive ones are red and relatively cold. We have already named the temperatures of the hottest and coldest stars (see above). Now we know that the highest temperatures correspond to blue stars, the lowest to red ones. Let us clarify that in this paragraph we were talking about the temperatures of the visible surfaces of stars, because in the center of stars (in their cores) the temperature is much higher, but it is also the highest in massive blue stars.

    The spectrum of a star and its temperature are closely related to the color index, i.e., to the ratio of the brightness of the star in the yellow and blue ranges of the spectrum. Planck's law, which describes the distribution of energy in the spectrum, gives an expression for the color index: C.I. = 7200/T 0.64. Cold stars have a higher color index than hot ones, i.e., cold stars are relatively brighter in yellow rays than in blue ones. Hot (blue) stars appear brighter on conventional photographic plates, while cool stars appear brighter to the eye and special photographic emulsions that are sensitive to yellow rays.
    Scientists have formulated physical laws that relate color and temperature. The hotter the body, the greater the radiation energy from its surface and the shorter the length of the emitted waves. Therefore, if a body radiates in the blue wavelength range, then it is hotter than a body that radiates red.
    Atoms of hot gases of stars emit photons. The hotter the gas, the higher the photon energy and the shorter their wave. Therefore, the hottest new stars emit in the blue-white range. As their nuclear fuel is used up, the stars cool down. Therefore, old, cooling stars radiate in the red range of the spectrum. Middle-aged stars, such as the Sun, radiate in the yellow range.
    Our Sun is relatively close to us, and therefore we clearly see its color. Other stars are so far away from us that even with the help of powerful telescopes we cannot say with certainty what color they are. To clarify this issue, scientists use a spectrograph - a device for detecting the spectral composition of starlight.
    HARVARD SPECTRAL CLASSIFICATION gives a temperature dependence of the color of a star, for example: 35004900 - orange, 800011000 white, 2600035000 blue, etc. http://www.pockocmoc.ru/color.php

    And another important fact: the dependence of the color of the star's glow on the mass.
    More massive normal stars have higher surface and interior temperatures. They quickly burn their nuclear fuel - hydrogen, which, in general, consists of almost all stars. Which of the two normal stars is more massive can be judged by its color: blue ones are heavier than white ones, white ones are yellow, yellow ones are orange, orange ones are red.

Multicolored stars in the sky. Shot with enhanced colors

The color palette of stars is wide. Blue, yellow and red - shades are visible even through the atmosphere, which usually distorts the outlines of cosmic bodies. But where does the color of a star come from?

The origin of the color of the stars

The secret of the multicolored stars has become an important tool for astronomers - the color of the stars helped them to recognize the surfaces of stars. It was based on a remarkable natural phenomenon - the ratio between the substance and the color of the light emitted by it.

You have probably already made your own observations on this subject. A filament of low-power 30-watt light bulbs glows orange - and when the mains voltage drops, the filament barely glows red. Stronger bulbs glow yellow or even white. And the welding electrode during operation and the quartz lamp glow blue. However, in no case should you look at them - their energy is so great that it can easily damage the retina of the eye.

Accordingly, the hotter the object, the closer its color of its glow to blue - and the colder, the closer to dark red. The stars are no exception: the same principle applies to them. The influence of a star on its color is very insignificant - the temperature can hide individual elements, ionizing them.

But it is the radiation of a star that helps to find out its composition. The atoms of each substance have their own unique capacity. Light waves of some colors pass through them without hindrance, when others stop - in fact, scientists determine chemical elements from the blocked ranges of light.

The mechanism of "coloring" stars

What is the physical background of this phenomenon? The temperature is characterized by the speed of movement of the molecules of the substance of the body - the higher it is, the faster they move. This affects the length that pass through the substance. A hot environment shortens the waves, and a cold one, on the contrary, lengthens them. And the visible color of the light beam is just determined by the wavelength of the light: short waves are responsible for blue hues, and long ones for red ones. White color is obtained as a result of the imposition of multispectral rays.