What stars are white. Stars
If you look closely at the night sky, it is easy to notice that the stars looking at us differ in color. Bluish, white, red, they shine evenly or flicker like a Christmas tree garland. In a telescope, color differences become more apparent. The reason for this diversity lies in the temperature of the photosphere. And, contrary to a logical assumption, the hottest are not red, but blue, white-blue and white stars. But first things first.
Spectral classification
Stars are huge hot balls of gas. The way we see them from Earth depends on many parameters. For example, stars don't actually twinkle. It is very easy to be convinced of this: it is enough to remember the Sun. The flickering effect occurs due to the fact that the light coming from cosmic bodies to us overcomes the interstellar medium, full of dust and gas. Another thing is color. It is a consequence of the heating of the shells (especially the photosphere) to certain temperatures. The true color may differ from the visible one, but the difference is usually small.
Today, the Harvard spectral classification of stars is used all over the world. It is a temperature one and is based on the shape and relative intensity of the spectrum lines. Each class corresponds to the stars of a certain color. The classification was developed at the Harvard Observatory in 1890-1924.
One Shaved Englishman Chewing Dates Like Carrots
There are seven main spectral classes: O-B-A-F-G-K-M. This sequence reflects a gradual decrease in temperature (from O to M). To remember it, there are special mnemonic formulas. In Russian, one of them sounds like this: "One Shaved Englishman Chewed Dates Like Carrots." Two more are added to these classes. The letters C and S denote cold luminaries with metal oxide bands in the spectrum. Consider the star classes in more detail:
- Class O is characterized by the highest surface temperature (from 30 to 60 thousand Kelvin). Stars of this type exceed the Sun in mass by 60, and in radius - by 15 times. Their visible color is blue. In terms of luminosity, they are ahead of our star by more than a million times. The blue star HD93129A, belonging to this class, is characterized by one of the highest luminosity among known cosmic bodies. According to this indicator, it is ahead of the Sun by 5 million times. The blue star is located at a distance of 7.5 thousand light years from us.
- Class B has a temperature of 10-30 thousand Kelvin, a mass 18 times greater than the same parameter of the Sun. These are white-blue and white stars. Their radius is 7 times greater than that of the Sun.
- Class A is characterized by a temperature of 7.5-10 thousand Kelvin, a radius and mass exceeding 2.1 and 3.1 times, respectively, the similar parameters of the Sun. These are white stars.
- Class F: temperature 6000-7500 K. The mass is 1.7 times greater than the sun, the radius is 1.3. From Earth, such stars also look white, their true color is yellowish white.
- Class G: temperature 5-6 thousand Kelvin. The Sun belongs to this class. The visible and true color of such stars is yellow.
- Class K: temperature 3500-5000 K. The radius and mass are less than solar, they are 0.9 and 0.8 of the corresponding parameters of the star. The color of these stars seen from Earth is yellowish-orange.
- Class M: temperature 2-3.5 thousand Kelvin. Mass and radius - 0.3 and 0.4 from similar parameters of the Sun. From the surface of our planet, they look red-orange. Beta Andromedae and Alpha Chanterelles belong to the M class. The bright red star familiar to many is Betelgeuse (Alpha Orionis). It is best to look for it in the sky in winter. The red star is located above and slightly to the left of Orion's belt.
Each class is divided into subclasses from 0 to 9, that is, from the hottest to the coldest. The numbers of stars indicate belonging to a certain spectral type and the degree of heating of the photosphere in comparison with other luminaries in the group. For example, the Sun belongs to the class G2.
visual whites
Thus, star classes B through F can look white from Earth. And only objects belonging to the A-type actually have this coloration. So, the star Saif (the constellation Orion) and Algol (beta Perseus) to an observer not armed with a telescope will seem white. They belong to spectral class B. Their true color is blue-white. Also appearing white are Mythrax and Procyon, the brightest stars in the celestial drawings of Perseus and Canis Minor. However, their true color is closer to yellow (class F).
Why are stars white to an earthly observer? The color is distorted due to the vast distance separating our planet from similar objects, as well as voluminous clouds of dust and gas, often found in space.
Class A
White stars are characterized by a not so high temperature as representatives of the O and B classes. Their photosphere heats up to 7.5-10 thousand Kelvin. Spectral class A stars are much larger than the Sun. Their luminosity is also greater - about 80 times.
In the spectra of A stars, hydrogen lines of the Balmer series are strongly pronounced. The lines of other elements are noticeably weaker, but they become more significant as you move from subclass A0 to A9. Giants and supergiants belonging to the spectral class A are characterized by slightly less pronounced hydrogen lines than main sequence stars. In the case of these luminaries, the lines become more noticeable heavy metals.
Many peculiar stars belong to the spectral class A. This term refers to luminaries that have noticeable features in the spectrum and physical parameters, which makes it difficult to classify them. For example, rather rare stars of the Bootes lambda type are characterized by a lack of heavy metals and very slow rotation. Peculiar luminaries also include white dwarfs.
Class A includes such bright objects in the night sky as Sirius, Menkalinan, Aliot, Castor and others. Let's get to know them better.
Alpha Canis Major
Sirius is the brightest, though not the closest, star in the sky. The distance to it is 8.6 light years. For an earthly observer, it seems so bright because it has an impressive size and yet is not as far removed as many other large and bright objects. The closest star to the Sun is Alpha Centauri. Sirius in this list is in fifth place.
It belongs to the constellation Canis Major and is a system of two components. Sirius A and Sirius B are separated by 20 astronomical units and rotate with a period of just under 50 years. The first component of the system, a main-sequence star, belongs to the spectral type A1. Its mass is twice that of the sun, and its radius is 1.7 times. It can be observed with the naked eye from Earth.
The second component of the system is a white dwarf. The star Sirius B is almost equal to our luminary in mass, which is not typical for such objects. Typically, white dwarfs are characterized by a mass of 0.6-0.7 solar masses. At the same time, the dimensions of Sirius B are close to those of the earth. It is assumed that the white dwarf stage began for this star about 120 million years ago. When Sirius B was located on the main sequence, it was probably a luminary with a mass of 5 solar masses and belonged to the spectral class B.
Sirius A, according to scientists, will move to the next stage of evolution in about 660 million years. Then it will turn into a red giant, and a little later - into a white dwarf, like its companion.
Alpha Eagle
Like Sirius, many white stars, whose names are given below, are well known not only to people who are fond of astronomy because of their brightness and frequent mention in the pages of science fiction literature. Altair is one of those luminaries. Alpha Eagle is found, for example, in Ursula le Guin and Steven King. In the night sky, this star is clearly visible due to its brightness and relatively close proximity. The distance separating the Sun and Altair is 16.8 light years. Of the stars of spectral class A, only Sirius is closer to us.
Altair is 1.8 times as massive as the Sun. His characteristic feature is a very fast rotation. The star makes one rotation around its axis in less than nine hours. The rotation speed near the equator is 286 km/s. As a result, the "nimble" Altair will be flattened from the poles. In addition, due to the elliptical shape, the temperature and brightness of the star decrease from the poles to the equator. This effect is called "gravitational darkening".
Another feature of Altair is that its brilliance changes over time. It belongs to the Delta Shield type variables.
Alpha Lyrae
Vega is the most studied star after the Sun. Alpha Lyrae is the first star to have its spectrum determined. She also became the second luminary after the Sun, captured in the photograph. Vega was also among the first stars to which scientists measured the distance using the parlax method. For a long period, the brightness of the star was taken as 0 when determining the magnitudes of other objects.
Lyra's alpha is well known to both the amateur astronomer and the simple observer. It is the fifth brightest among the stars, and is included in the Summer Triangle asterism along with Altair and Deneb.
The distance from the Sun to Vega is 25.3 light years. Its equatorial radius and mass are 2.78 and 2.3 times larger than the similar parameters of our star, respectively. The shape of a star is far from being a perfect ball. The diameter at the equator is noticeably larger than at the poles. The reason is the huge rotation speed. At the equator, it reaches 274 km / s (for the Sun, this parameter is slightly more than two kilometers per second).
One of the features of Vega is the dust disk that surrounds it. It is presumed that it resulted from a large number collisions of comets and meteorites. The dust disk revolves around the star and is heated by its radiation. As a result, the intensity of the infrared radiation of Vega increases. Not so long ago, asymmetries were discovered in the disk. Their likely explanation is that the star has at least one planet.
Alpha Gemini
The second brightest object in the constellation Gemini is Castor. He, like the previous luminaries, belongs to the spectral class A. Castor is one of the most bright stars night sky. In the corresponding list, he is on the 23rd place.
Castor is a multiple system consisting of six components. The two main elements (Castor A and Castor B) revolve around a common center of mass with a period of 350 years. Each of the two stars is a spectral binary. The Castor A and Castor B components are less bright and presumably belong to the M spectral type.
Castor C was not immediately connected to the system. Initially, it was designated as an independent star YY Gemini. In the process of researching this region of the sky, it became known that this luminary was physically connected with the Castor system. The star revolves around a center of mass common to all components with a period of several tens of thousands of years and is also a spectral binary.
Beta Aurigae
The celestial drawing of the Charioteer includes approximately 150 "points", many of them are white stars. The names of the luminaries will say little to a person far from astronomy, but this does not detract from their significance for science. by the most bright object celestial pattern, belonging to the spectral class A, is Mencalinan or Beta Aurigae. The name of the star in Arabic means "shoulder of the owner of the reins."
Mencalinan is a ternary system. Its two components are subgiants of spectral class A. The brightness of each of them exceeds the similar parameter of the Sun by 48 times. They are separated by a distance of 0.08 astronomical units. The third component is a red dwarf at a distance of 330 AU from the pair. e.
Epsilon Ursa Major
The brightest "point" in perhaps the most famous constellation in the northern sky (Ursa Major) is Aliot, also classified as class A. Apparent value- 1.76. In the list of the brightest luminaries, the star takes 33rd place. Alioth enters the asterism of the Big Dipper and is located closer to the bowl than other luminaries.
The Aliot spectrum is characterized by unusual lines that fluctuate with a period of 5.1 days. It is assumed that the features are associated with the influence of the magnetic field of the star. Fluctuations in the spectrum, according to the latest data, may occur due to the proximity of a cosmic body with a mass of almost 15 Jupiter masses. Whether this is so is still a mystery. Her, like other secrets of the stars, astronomers are trying to understand every day.
white dwarfs
The story about white stars will be incomplete if we do not mention that stage in the evolution of the stars, which is designated as the "white dwarf". Such objects got their name due to the fact that the first discovered of them belonged to the spectral class A. It was Sirius B and 40 Eridani B. Today, white dwarfs are called one of the options for the final stage of a star's life.
Let us dwell in more detail on the life cycle of the luminaries.
Star evolution
Stars are not born in one night: any of them goes through several stages. First, a cloud of gas and dust begins to shrink under the influence of its own gravitational forces. Slowly, it takes the form of a ball, while the energy of gravity turns into heat - the temperature of the object rises. At the moment when it reaches a value of 20 million Kelvin, the reaction of nuclear fusion begins. This stage is considered the beginning of the life of a full-fledged star.
Suns spend most of their time on the main sequence. Hydrogen cycle reactions are constantly going on in their depths. The temperature of the stars may vary. When all the hydrogen in the nucleus ends, a new stage of evolution begins. Now helium is the fuel. At the same time, the star begins to expand. Its luminosity increases, while the surface temperature, on the contrary, decreases. The star leaves the main sequence and becomes a red giant.
The mass of the helium core gradually increases, and it begins to shrink under its own weight. The red giant stage ends much faster than the previous one. The path that further evolution will take depends on the initial mass of the object. Low-mass stars at the red giant stage begin to swell. As a result of this process, the object sheds its shells. A planetary nebula and a bare core of a star are formed. In such a nucleus, all fusion reactions are completed. It is called a helium white dwarf. More massive red giants (up to a certain limit) evolve into carbon white dwarfs. They have heavier elements than helium in their cores.
Characteristics
White dwarfs - bodies, in mass, as a rule, very close to the Sun. At the same time, their size corresponds to the earth. The colossal density of these cosmic bodies and the processes taking place in their depths are inexplicable from the point of view of classical physics. The secrets of the stars helped to reveal quantum mechanics.
The substance of white dwarfs is an electron-nuclear plasma. It is almost impossible to design it even in a laboratory. Therefore, many characteristics of such objects remain incomprehensible.
Even if you study the stars all night long, you will not be able to detect at least one white dwarf without special equipment. Their luminosity is much less than that of the sun. According to scientists, white dwarfs make up approximately 3 to 10% of all objects in the Galaxy. However, to date, only those of them have been found that are located no further than 200-300 parsecs from the Earth.
White dwarfs continue to evolve. Immediately after formation, they have a high surface temperature, but cool quickly. A few tens of billions of years after the formation, according to the theory, the white dwarf turns into a black dwarf - a body that does not emit visible light.
A white, red or blue star for the observer differs primarily in color. The astronomer looks deeper. Color for him immediately tells a lot about the temperature, size and mass of the object. A blue or bright blue star is a giant hot ball, far ahead of the Sun in all respects. White luminaries, examples of which are described in the article, are somewhat smaller. Star numbers in various catalogs also tell professionals a lot, but not all. A large amount of information about the life of distant space objects has either not yet been explained, or remains not even discovered.
Stars of different colors
Our Sun is a pale yellow star. In general, the color of the stars is a stunningly diverse palette of colors. One of the constellations is called the "Jewel Box". Sapphire blue stars are scattered across the black velvet of the night sky. Between them, in the middle of the constellation, is a bright orange star.
Differences in the color of the stars
The differences in the color of the stars are explained by the fact that the stars have different temperatures. That's why it happens. Light is wave radiation. The distance between the crests of one wave is called its length. Waves of light are very short. How much? Try dividing an inch by 250000 equal parts(1 inch equals 2.54 centimeters). Several of these parts make up the length of a light wave.
Despite such an insignificant wavelength of light, the slightest difference between the sizes of light waves dramatically changes the color of the picture that we observe. This is due to the fact that light waves of different wavelengths are perceived by us as different colors. For example, the wavelength of red is one and a half times longer than the wavelength of blue. White color is a beam consisting of photons of light waves of different lengths, that is, from rays of different colors.
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flame color
We know from everyday experience that the color of bodies depends on their temperature. Put the iron poker on the fire. When heated, it first turns red. Then she blushes even more. If the poker could be heated even more without melting it, then it would turn from red to orange, then yellow, then white, and finally blue-white.
The sun is a yellow star. The temperature on its surface is 5,500 degrees Celsius. The temperature on the surface of the hottest blue star exceeds 33,000 degrees.
Physical laws of color and temperature
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. Blue colour has a shorter wavelength than red. Therefore, if a body emits in the blue wavelength range, then it is hotter than a body emitting red light. Atoms of the hot gases of stars emit particles called photons. The hotter the gas, the higher the photon energy and the shorter their wave.
Many people think that all the stars in the sky are white. (Except for the Sun, which, of course, yellow.) Surprisingly, but in fact it's just the opposite: ours, and the stars come in different colors - bluish, white, yellowish, orange and even red!
Another question, Can you see the color of stars with the naked eye?? Dim stars appear white simply because they are too weak to excite cones in the retina of our eyes - special receptor cells responsible for color vision. Rods sensitive to weak light do not distinguish colors. That is why in the dark all cats are gray and all stars are white.
bright star colors
What about bright stars?
Let's look at the constellation of Orion, or rather, at its two brightest stars, Rigel and Betelgeuse. (Orion is the central constellation of the winter sky. It is 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 tint. Photo: Bill Dickinson/APOD
Even a cursory 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 do 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 stars, and yellow stars are hotter than orange stars. The hottest stars are bluish white, while the coldest are red. In this way, Rigel is much hotter than Betelgeuse.
What color is Rigel really?
Sometimes, though, it's not so obvious. On a frosty or windy night, when the air is restless, you can observe a strange thing - Rigel quickly changes its brightness (in other words, flickers) and shimmers in different colors! Sometimes it looks like it's blue, sometimes it looks like it's white, and then it flashes red for a moment! It turns out that Rigel is not a bluish-white star at all - it is generally unclear what color it is!
Blue Rigel and reflection nebula Witch's Head. Photo: Michael Heffner/Flickr.com
The 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 change are much more noticeable than those of the stars in the neighborhood.
Although stars come in a variety of colors, white and reddish are best seen with the naked eye. Of all the bright stars, perhaps only Vega looks 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 spyglasses - will show a much brighter and wider palette of star colors. You will 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! Truth, there are no green stars in nature(why is a separate question), this is an optical illusion, although very beautiful! Observation of 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 to varying degrees of chromatic aberration, and reflector mirrors reflect light of all colors equally.
It is very interesting to observe the multi-colored stars, first with the naked eye, and then with binoculars or a telescope. (When looking through a telescope, use the lowest magnification.)
The table below shows the colors for 8 bright stars. The brightness of the stars is given in stellar magnitudes. The letter v means that the brightness of the star is variable - for physical reasons it shines either brighter or dimmer.
Star | Constellation | Shine | Color | Evening visibility |
---|---|---|---|---|
Sirius | Big Dog | -1.44 | White, but often shimmers and shimmers in different 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 highly shimmery and iridescent 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 |
Colorful stars in the December sky
In December, you can find a whole dozen bright colored stars! We have already talked about the red Betelgeuse and the bluish-white Rigel. On exceptionally calm nights, Sirius is striking in its whiteness. Star Chapel in the constellation Auriga to the naked eye it seems almost white, but in 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 is 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 of Gemini you will find a pale orange glow.
Pollux is the brightest star in the constellation Gemini. Photo: Fred Espanak
In the end, I note that the colors of the stars that we observe visually depend largely 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. Do an experiment! Look at the stars in the table above for yourself - with the naked eye and through an optical instrument. Rate their color!
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what color are the stars? and why?
- Stars come in all colors of the rainbow. Because they have different temperatures and composition.
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http://www.pockocmoc.ru/color.php - 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 - 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. - The hottest white and blue flowers the coldest red ones, but even then they have a temperature higher than any molten metal
- is the sun white?
- The perception of color is purely subjective, it depends on the reaction of the retina of the observer's eye.
- in the sky? I know that there are blue ones, and yellow ones, and white ones. our sun is a yellow dwarf
- 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.
- 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.phpAnd more important fact: 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.
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 are 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 " Milky Way", maybe 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 may rise so much that a reaction will begin. thermonuclear fusion- 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 in the sky polar star, 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 the energy lost 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 a 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 stellar magnitude of such objects? 3m-0m (I and III class of 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 the 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 small 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 will pass through a strong gravitational field. However, in most cases, variability is associated with unstable internal processes. AT 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 shell 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 whose brightness distribution 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
New star- type of cataclysmic variables. 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
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.