The color of the stars is white blue yellow. What kind of stars are there?

Many people think that all the stars in the sky are white. (Except for the Sun, which, of course, yellow.) Surprisingly, but in fact everything is just the opposite: ours, and stars come in different colors - bluish, white, yellowish, orange and even red!

Another question, is it possible to see the color of stars with the naked eye? Dim stars appear white simply because they are too faint to excite the cones in the retina of our eyes, the special receptor cells responsible for color vision. The rods, sensitive to weak light, do not distinguish colors. That is why in the dark all cats are gray and all stars are white.

Colors of bright stars

What about bright stars?

Let's look at the constellation Orion, or rather, at its two brightest stars, Rigel and Betelgeuse. (Orion is the central constellation of the winter sky. Observed in the evenings in the south from late November to March.)

The star Betelgeuse stands out among others in the constellation Orion with its reddish hue. Photo: Bill Dickinson/APOD

Even a quick glance is enough to notice the red color of Betelgeuse and the bluish-white color of Rigel. This is not an apparent phenomenon - the stars really have different colors. The difference in color is determined only by the temperature on the surfaces of these stars. White stars are hotter than yellow ones, and yellow ones, in turn, are hotter than orange ones. The hottest stars are bluish-white, while the coolest are red. Thus, Rigel is much hotter than Betelgeuse.

What color is Rigel actually?

Sometimes, however, everything is not so obvious. On a frosty or windy night when the air is not calm, you may observe strange thing- The crossbar quickly, quickly changes its brightness (to put it simply, it flickers) and shimmers in different colors! Sometimes it seems that it is blue, sometimes it seems that it is white, and then for a moment it appears red! It turns out that Rigel is not a bluish-white star at all - it is not clear what color it is!

Blue Rigel and the Witch's Head reflection nebula. Photo: Michael Heffner/Flickr.com

Responsibility for this phenomenon lies entirely with the Earth's atmosphere. Low above the horizon (and Rigel never rises high in our latitudes), the stars often twinkle and shimmer in different colors. Their light passes through a very large thickness of the atmosphere before reaching our eyes. Along the way, it is refracted and deflected in layers of air with different temperatures and densities, creating the effect of trembling and rapid color changes.

The best example of a star that shimmers in different colors is white. Sirius, which is located in the sky next to Orion. Sirius is the brightest star in the night sky and therefore its twinkling and rapid color changes are much more noticeable than those of neighboring stars.

Although stars come in a variety of colors, the ones best distinguished by the naked eye are white and reddish. Of all the bright stars, perhaps only Vega appears distinctly bluish.

Vega looks like a sapphire in a telescope. Photo: Fred Espanak

Colors of stars in telescopes and binoculars

Optical instruments - telescopes, binoculars and spotting scopes - will reveal a much brighter and wider palette of star colors. You'll see bright orange and yellow stars, bluish-white, yellowish-white, golden and even greenish stars! How real are these colors?

Basically they are all real! Is it true, There are no green stars in nature(why is a separate question), this is an optical illusion, although a very beautiful one! Observing greenish and even emerald-green stars is only possible when there is a yellow or yellowish-orange star very close.

A reflecting telescope reproduces colors much more accurately than a refractor, since lens telescopes suffer from chromatic aberration to one degree or another, and reflector mirrors reflect light of all colors equally.

It's very interesting to watch colorful stars first with the naked eye and then with binoculars or a telescope. (When viewing through a telescope, use the lowest magnification.)

The table below shows the colors for 8 bright stars. The brightness of stars is given in magnitude. The letter v means that the brightness of the star is variable - it shines, due to physical reasons, either brighter or dimmer.

Star	Constellation	Shine	Color	Evening visibility
Sirius	Big Dog	-1.44	White, but often shimmers strongly and changes colors due to atmospheric conditions	November - March
Vega	Lyra	0.03	Blue	All year round
Chapel	Auriga	0.08	Yellow	All year round
Rigel	Orion	0.18	Bluish-white, but often shimmers strongly and changes colors due to atmospheric conditions	November - April
Procyon	Small Dog	0.4	White	November - May
Aldebaran	Taurus	0.87	Orange	October - April
Pollux	Twins	1.16	Pale orange	November - June
Betelgeuse	Orion	0.45v	Orange-red	November - April

Multi-colored stars in the December sky

There are a dozen brightly colored stars to be found in December! We have already talked about red Betelgeuse and bluish-white Rigel. On exceptionally calm nights, Sirius amazes with its whiteness. Star Chapel in the constellation Auriga it appears almost white to the naked eye, but through a telescope it reveals a distinct yellowish tint.

Be sure to take a look at Vega, which from August to December is visible in the evenings high in the sky in the south and then in the west. It’s not for nothing that Vega is called the heavenly sapphire - its blue color is so deep when observed through a telescope!

Finally, at the star Pollux From the constellation Gemini you will notice a pale orange glow.

Pollux, the brightest star in the constellation Gemini. Photo: Fred Espanak

In conclusion, I note that the colors of the stars that we observe visually largely depend on the sensitivity of our eyes and subjective perception. Perhaps you will object to me on all points and say that the color of Pollux is deep orange, and Betelgeuse is yellowish-red. Try an experiment! Look at the stars in the table above for yourself - with the naked eye and through an optical instrument. Give your opinion on their color!

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We never think that perhaps there is some kind of life other than our planet, other than ours. solar system. Perhaps there is life on one of the planets orbiting a blue or white or red, or maybe a yellow star. Perhaps there is another planet like this, on which the same people live, but we still don’t know anything about it. Our satellites and telescopes have discovered a number of planets that may have life, but these planets are tens of thousands and even millions of light years away.

Blue stragglers are stars that are blue in color.

Stars located in globular star clusters, whose temperature is higher than that of ordinary stars, and whose spectrum is characterized by a significant shift to the blue region than that of cluster stars with a similar luminosity, are called blue stragglers. This feature allows them to stand out relative to other stars in this cluster on the Hertzsprung-Russell diagram. The existence of such stars refutes all theories of stellar evolution, the essence of which is that stars that arose in the same period of time are expected to be located in a well-defined region of the Hertzsprung-Russell diagram. In this case, the only factor that affects the exact location of the star is its initial mass. The frequent appearance of blue stragglers outside the above curve may confirm the existence of such a thing as anomalous stellar evolution.

Experts trying to explain the nature of their occurrence have put forward several theories. The most likely of them indicates that these blue stars were double in the past, after which they began to undergo or are now undergoing a merger process. The result of the merger of two stars is the emergence of a new star, which has a much greater mass, brightness and temperature than stars of the same age.

If this theory could somehow be proven correct, the theory of stellar evolution would be free of the problem of blue stragglers. The resulting star would have a larger amount of hydrogen, which would behave similarly to a young star. There are facts that support this theory. Observations have shown that stragglers are most often found in the central regions of globular clusters. As a result of the predominant number of unit-volume stars there, close passages or collisions become more likely.

To test this hypothesis, it is necessary to study the pulsation of blue stragglers, because There may be some differences between the asteroseismological properties of merged stars and normally pulsating variables. It is worth noting that measuring pulsations is quite difficult. This process is also negatively affected by the overcrowding of the starry sky, small fluctuations in the pulsations of blue stragglers, as well as the rarity of their variables.

One example of a merger could be observed in August 2008, when such an incident affected object V1309, the brightness of which, after discovery, increased several tens of thousands of times, and after several months returned to its original value. As a result of 6 years of observations, scientists came to the conclusion that this object is two stars whose orbital period around each other is 1.4 days. These facts led scientists to believe that in August 2008, the process of merging these two stars took place.

Blue stragglers are characterized by high torque. For example, the rotation speed of the star, which is located in the middle of the 47 Tucanae cluster, is 75 times higher than the rotation speed of the Sun. According to the hypothesis, their mass is 2-3 times greater than the mass of other stars that are located in the cluster. Also, through research, it was found that if blue stars are located close to any other stars, then the latter will have a lower percentage of oxygen and carbon than their neighbors. Presumably, stars pull these substances from other stars moving in their orbit, as a result of which their brightness and temperature increase. In “robbed” stars, places are discovered where the process of transformation of the original carbon into other elements took place.

Names of blue stars - examples

Rigel, Gamma Parus, Alpha Giraffe, Zeta Orionis, Tau Canis Major, Zeta Puppis

White stars are white stars

Friedrich Bessel, who headed the Königsberg Observatory, made an interesting discovery in 1844. The scientist noticed the slightest deviation of the brightest star in the sky, Sirius, from its trajectory across the sky. The astronomer suggested that Sirius had a satellite, and also calculated the approximate period of rotation of stars around their center of mass, which was about fifty years. Bessel did not find adequate support from other scientists, because No one was able to detect the satellite, although its mass should have been comparable to Sirius.

And only 18 years later, Alvan Graham Clark, who was testing the best telescope of those times, discovered a dim white star near Sirius, which turned out to be its satellite, called Sirius B.

The surface of this white star is heated to 25 thousand Kelvin, and its radius is small. Taking this into account, scientists concluded that the satellite has a high density (at the level of 106 g/cm3, while the density of Sirius itself is approximately 0.25 g/cm3, and that of the Sun is 1.4 g/cm3). 55 years later (in 1917), another white dwarf was discovered, named after the scientist who discovered it - van Maanen's star, which is located in the constellation Pisces.

Names of white stars - examples

Vega in the constellation Lyra, Altair in the constellation Aquila (visible in summer and autumn), Sirius, Castor.

Yellow stars – yellow stars

Yellow dwarfs are usually called small main sequence stars whose mass is within the mass of the Sun (0.8-1.4). Judging by the name, such stars have a yellow glow, which is released during the thermonuclear process of fusion from hydrogen to helium.

The surface of such stars heats up to a temperature of 5-6 thousand Kelvin, and their spectral classes range between G0V and G9V. A yellow dwarf lives for about 10 billion years. The combustion of hydrogen in a star causes it to multiply in size and become a red giant. One example of a red giant is Aldebaran. Such stars can form planetary nebulae by shedding their outer layers of gas. In this case, the core transforms into a white dwarf, which has a high density.

If we take into account the Hertzsprung-Russell diagram, then on it the yellow stars are located in the central part of the main sequence. Since the Sun can be called a typical yellow dwarf, its model is quite suitable for considering the general model of yellow dwarfs. But there are other characteristic yellow stars in the sky, whose names are Alhita, Dabikh, Toliman, Khara, etc. These stars are not very bright. For example, the same Toliman, which, if you do not take into account Proxima Centauri, is closest to the Sun, has a 0th magnitude, but at the same time its brightness is the highest among all yellow dwarfs. This star is located in the constellation Centaurus, and it is also part of a complex system that includes 6 stars. The spectral class of Toliman is G. But Dabih, located 350 light years from us, belongs to the spectral class F. But its high brightness is due to the presence of a nearby star belonging to the spectral class - A0.

In addition to Toliman, spectral class G has HD82943, which is located on the main sequence. This star, due to its chemical composition and temperature similar to the Sun, also has two large planets. However, the shape of the orbits of these planets is far from circular, so their approaches to HD82943 occur relatively often. Currently, astronomers have been able to prove that this star used to have a much larger number of planets, but over time it absorbed them all.

Names of yellow stars - examples

Toliman, star HD 82943, Hara, Dabih, Alhita

Red stars are red stars

If at least once in your life you have seen through the lens of your telescope red stars in the sky that were burning against a black background, then remembering this moment will help you more clearly imagine what will be written about in this article. If you have never seen such stars before, be sure to try to find them next time.

If you set out to compile a list of the brightest red stars in the sky, which can be easily found even with an amateur telescope, you will find that they are all carbon stars. The first red stars were discovered back in 1868. The temperature of such red giants is low, in addition, their outer layers are filled with huge amounts of carbon. If previously similar stars made up two spectral classes - R and N, now scientists have identified them into one general class– C. Each spectral class has subclasses - from 9 to 0. In this case, class C0 means that the star has a higher temperature, but is less red than stars of class C9. It is also important that all carbon-dominated stars are inherently variable: long-period, semi-regular or irregular.

In addition, two stars called red semi-regular variables were included in this list, the most famous of which is m Cephei. William Herschel became interested in its unusual red color and dubbed it “pomegranate.” Such stars are characterized by irregular changes in luminosity, which can last from a couple of tens to several hundred days. Such variable stars belong to class M (cool stars with surface temperatures from 2400 to 3800 K).

Considering the fact that all the stars in the rating are variables, it is necessary to bring some clarity to the notation. It is generally accepted that red stars have a name that consists of two components - a letter of the Latin alphabet and the name of a variable constellation (for example, T Hare). The first variable discovered in a given constellation is assigned the letter R, and so on, up to the letter Z. If there are many such variables, a double combination of Latin letters is provided for them - from RR to ZZ. This method allows you to “name” 334 objects. In addition, stars can be designated using the letter V in combination with a serial number (V228 Cygnus). The first column of the rating is reserved for the designation of variables.

The next two columns in the table indicate the location of the stars in the period 2000.0. As a result of the increased popularity of the Uranometria 2000.0 atlas among astronomy enthusiasts, the last column of the rating displays the search chart number for each star that is in the rating. In this case, the first digit is a display of the volume number, and the second is serial number cards.

The rating also displays the maximum and minimum brightness values ​​of stellar magnitudes. It is worth remembering that greater saturation of red color is observed in stars whose brightness is minimal. For stars whose period of variability is known, it is displayed as the number of days, but objects that do not have the correct period are displayed as Irr.

Finding a carbon star does not require much skill; it is enough that the capabilities of your telescope are enough to see it. Even if its size is small, its bright red color should attract your attention. Therefore, you should not be upset if you cannot detect them immediately. It is enough to use the atlas to find a nearby bright star, and then move from it to the red one.

Different observers see carbon stars differently. To some, they resemble rubies or an ember burning in the distance. Others see crimson or blood-red shades in such stars. To begin with, the rating has a list of the six brightest red stars, which, once found, you can fully enjoy their beauty.

Names of red stars - examples

Star color differences

There is a huge variety of stars with indescribable color shades. As a result, even one constellation received the name “Jewel Box”, the basis of which is made up of blue and sapphire stars, and in its very center is a brightly shining orange star. If we consider the Sun, it has a pale yellow color.

A direct factor influencing the difference in color between stars is their surface temperature. This is explained simply. Light by its nature is radiation in the form of waves. The wavelength is the distance between its crests and is very small. To imagine it, you need to divide 1 cm into 100 thousand identical parts. Several of these particles will make up the wavelength of light.

Considering that this number turns out to be quite small, every, even the most insignificant, change in it will be the reason why the picture we observe will change. After all, our vision perceives different wavelengths of light as different colors. For example, blue has waves whose length is 1.5 times shorter than that of red.

Also, almost every one of us knows that temperature can have a very direct effect on the color of bodies. For example, you can take any metal object and put it on the fire. It will turn red while heating. If the temperature of the fire increased significantly, the color of the object would change - from red to orange, from orange to yellow, from yellow to white, and finally from white to blue-white.

Since the Sun has a surface temperature of around 5.5 thousand 0 C, it is a typical example of yellow stars. But the hottest blue stars can heat up to 33 thousand degrees.

Color and temperature were linked by scientists using physical laws. How the temperature of a body is directly proportional to its radiation and inversely proportional to the wavelength. Waves of blue color have shorter wavelengths compared to red. Hot gases emit photons, the energy of which is directly proportional to temperature and inversely proportional to wavelength. That is why the hottest stars are characterized by a blue-blue emission range.

Since nuclear fuel on stars is not unlimited, it tends to be consumed, which leads to the cooling of stars. Therefore, middle-aged stars are yellow, and we see old stars as red.

As a result of the fact that the Sun is very close to our planet, its color can be accurately described. But for stars that are a million light years away, the task becomes more complicated. This is what a device called a spectrograph is used for. Scientists pass through it the light emitted by stars, as a result of which it is possible to spectrally analyze almost any star.

In addition, using the color of a star, you can determine its age, because mathematical formulas allow the use of spectral analysis to determine the temperature of a star, from which it is easy to calculate its age.

Video secrets of the stars watch online

Multi-colored stars in the sky. Photo 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?

Origin of star color

The secret of the different colors of stars became an important tool for astronomers - the color of the stars helped them recognize the surfaces of stars. It was based on a remarkable a natural phenomenon- the relationship between a substance and the color of the light it emits.

You have probably already made observations on this topic yourself. The 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 and the quartz lamp glow blue during operation. However, you should never look at them - their energy is so great that it can easily damage the retina.

Accordingly, the hotter the object, the closer its glow color is to blue - and the colder it is, 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 small - temperature can hide individual elements, ionizing them.

But it is the star’s radiation that helps determine its composition. The atoms of each substance have their own unique carrying capacity. Light waves of some colors pass through them unhindered, when others stop - in fact, scientists determine by blocked ranges of light chemical elements.

The mechanism of “coloring” stars

What is the physical basis for this phenomenon? Temperature is characterized by the speed of movement of the molecules of a body substance - the higher it is, the faster they move. This affects the length that passes through the substance. A hot environment shortens the waves, and a cold environment, on the contrary, lengthens them. And the visible color of a light beam is precisely determined by the wavelength of the light: short waves are responsible for blue shades, and long waves are responsible for red shades. White color is obtained as a result of the superposition of different spectral rays.

Look at the night sky, what kind of stars there are. On clear, dark nights with normal vision, you can see thousands of stars, some barely visible, others shining so brightly that they can be seen when the sky is still blue! Why are some stars brighter than others?

For two reasons. Some are simply closer to us, while others, although far away, are unimaginably large in size. Let's take a look at a small section of the southern sky.

Alpha Centauri(yellow), is one of the brightest stars in the night sky, it is similar to ours, only slightly larger and brighter, and has about the same color. The reason for its brightness is that it is (by cosmic standards) very close to us: only 4.4 light years.

But look at the second brightest star (the blue one just above) known as Beta Centauri.
Beta Centauri is not actually Alpha Centauri's neighbor. Although the yellow star is only 4.4 light years from Earth, Beta Centauri is located 530 light years from Earth, or more than 100 times further!

Why then does Beta Centauri shine almost as brightly as Alpha Centauri? Yes, because this is a different type of star! What kind of stars are there if we look by color. Yellow Alpha Centauri is "G-type", just like our Sun. And Beta Centauri is one of the blue stars, and belongs to the “B-type” stars.

Each star has 5 main parameters:1. Luminosity, 2. Color, 3. Temperature, 4. Size, 5. weight. These characteristics depend significantly on each other. The color depends on the temperature of the star, the intensity depends on the temperature and size.

Star color and temperature

Despite their shades, stars have three primary colors: red, yellow and blue. Our Sun is one of the yellow stars. The color depends on its temperature. The temperature of yellow stars on the surface reaches 6000° C. Red stars are cooler; their surface temperature is from 2000° C to 3000° C. And blue stars are considered the hottest, from 10,000° C to 100,000° C.

Everyone knows the three physical states of matter - solid, liquid and gaseous.. What happens to a substance when successively heated to high temperatures in a closed volume? - Sequential transition from one state of aggregation to another: solid- liquid - gas(due to an 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 components elementary particles- electrons and atomic nuclei. Plasma is the fourth state of matter in which the molecules or atoms of a substance are partially or completely destroyed under the influence of high temperatures or for other reasons. 99.9% of the matter in the Universe is in the plasma state.

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 size, luminosity and temperature change). The star becomes a variable star.

Variable star is a star whose brightness (visible brightness in the sky) changes over time. The causes of variability may 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 eclipsing variables stars whose variability is caused by mutual eclipses of their components(for example, β Persei - Algol. Its variability was first discovered in 1669 by the Italian economist and astronomer Geminiano Montanari).

Eclipsing variable stars are always double, those. consist of two closely spaced stars. Variable stars on star maps they are indicated by a circle:

Stars are not always balls. If a star rotates very quickly, then its shape is not spherical. The star contracts from the poles and becomes like a tangerine or 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 double star β Lyrae or Spica):

Stars are the main inhabitants of our Galaxy (our Galaxy is written with a capital letter). There are about 200 billion stars in it. 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% consists of interstellar gas, dust and all non-self-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 system to the Sun is the α Centauri system, consisting 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 sv. years, to Altair - 17 St. years. To Vega - 26 St. years. Before North Star- 830 St. years. To Deneb - 1,500 sv. years. For the first time in 1837, V.Ya. was able to determine the distance to another star (it was Vega). Struve.

The first star for which it was possible to obtain an image of the disk (and even some spots on it) is Betelgeuse (α Orionis). But this is because Betelgeuse is 500-800 times larger in diameter than the Sun (the star is pulsating). An image of Altair's disk (α Aquila) was also obtained, but this is because Altair is one of the closest stars.

The color of stars depends on the temperature of their outer layers. Temperature range - from 2,000 to 60,000 °C. The coolest stars are red, and the hottest are blue. By the color of a star you can judge how hot its outer layers are.

Examples of red stars: Antares (α Scorpii) and Betelgeuse (α Orionis).

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

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

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

Examples of white stars: Sirius (α Canis Majoris), 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 from the brightest of them. With binoculars and even more so with 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 have temperatures reaching millions of degrees at their centers. The Sun has about 15,000,000 °C at its center (the Kelvin scale is also used - the scale 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 heats up the stellar interior so much? It turns out that there are happening thermonuclear processes, as a result of which a huge amount of energy is released. Translated from Greek, “thermos” means warm. The main chemical element that stars are made of is hydrogen. It is this that 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, and 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.“The stars are the past of man, and man is the future of the star,” as they sometimes say figuratively.

The process of a star emitting energy in the form of electromagnetic waves and particles is called radiation. Stars emit 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 ( sunny wind) leads to the appearance of auroras on Earth and other planets. It is the solar wind that deflects the tails of comets in the direction opposite to the Sun.

Stars, of course, do not appear from the void (the space between stars is not an absolute vacuum). The materials are gas and dust. They are distributed unevenly 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-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 process of star birth to begin? The first is the mass of the cloud. If there is not enough matter, then, of course, the star will not appear. Second, compactness. If the cloud is too extended and loose, the processes of its compression cannot begin. Well, and thirdly, a seed is needed - i.e. a clot of dust and gas, which will later become the embryo of a star - a protostar. Protostar- this 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 appearance 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 Orion Nebula.

The main physical characteristics of a star are luminosity, mass and radius(or diameter), which are determined from observations. Knowing them as well chemical composition star (which is determined by its spectrum), one can calculate the model of the star, i.e. physical conditions in its depths, to explore the processes that occur 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 surrounding bodies. The mass of the Sun, for example, was determined from the known periods of revolution of the planets around it. Planets are not directly observed in other stars. Reliable measurement of mass is possible only for double stars (using Kepler’s law generalized by Newton III, nand then the error is 20-60%). About half of all the stars in our Galaxy are double. Stellar masses range from ≈0.08 to ≈100 solar masses.There are no stars with a mass less than 0.08 solar masses; 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 a star depends on its mass, i.e. the scenario according to which the star develops and evolves. Small, cold red dwarfs use hydrogen very sparingly and therefore their lives last hundreds of billions of years. The lifespan 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 fade away 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 old do not yet exist.

• Stars with mass 0,08 solar masses are brown dwarfs; their fate is constant compression 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 using up hydrogen begin to slowly compress, while heating up and becoming a white dwarf.
  

• Stars with mass 0,5-8 masses of the Sun at the end of their lives turn first into red giants and then into white dwarfs. 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, they first become red supergiants, then explode as supernovae (a supernova is not a new star, 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 very high mass and density. Black holes have neither supernatural nor magical powers, and are not “monsters of the Universe.” They simply have such a strong gravitational field that no radiation (neither visible - light, nor invisible) can leave them. That's why black holes are invisible. However, they can be detected by their effect on surrounding stars and nebulae. Black holes are a completely common phenomenon in the Universe and there is no need to 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 several kilometers (neutron stars) to 2,000 times the diameter of the Sun (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 supergiants have a density less than the density of air at 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 is 3.5 times greater,

Arcturus is 26 times larger

Polar is 30 times larger,

The crossbar is 70 times larger,

Deneb is 200 times larger,

Antares is 800 times larger,

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

Luminosity is total energy, emitted by an object (in this case stars) per unit time. The luminosity of stars is usually compared with the luminosity of the Sun (the luminosity of stars is expressed through the luminosity of the Sun). Sirius, for example, emits 22 times more energy than the Sun (the luminosity of Sirius is equal to 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, brightness) of a star in the earth’s sky depends on:

- distance to the star. If a star approaches us, its apparent brightness will gradually increase. And vice versa, as a star moves away from us, its apparent brightness will gradually decrease. If you take two identical stars, the one closer to us will appear brighter.

- on the temperature of the outer layers. The hotter a star is, the more light energy it sends into space, and the brighter it will appear. If a star cools down, then its apparent brightness in the sky will decrease. Two stars of the same size and at the same distances 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 cooler than the other, then it will appear less bright.

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

- from the absorption of light by clouds of cosmic dust and gas located 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 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 just before sunset), stars always appear dimmer than when they are overhead.

It is very important not to confuse the concepts of “appear” and “be”. A star can 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 talking about the brightness of a star in the earth’s sky, they use the phrase "apparent brightness" or "brilliance".

As already mentioned, there are double stars. But there are also triple (for example, α Centauri), and quadruple (for example, ε Lyra), and five, and six (for example, Castor), etc. 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 (they 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 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 disperse further over time.

Open clusters are typically located on or near the Milky Way band. On the contrary, globular clusters are located on starry sky away from the Milky Way.

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