Any star - yellow, blue or red - is a hot gas ball. The modern classification of luminaries is based on several parameters. These include surface temperature, size and brightness. The color of a star visible on a clear night depends mainly on the first parameter. The hottest luminaries are blue or even blue, the coldest are red. Yellow stars, examples of which are listed below, occupy a middle position on the temperature scale. Among the luminaries is the sun.
Differences
Bodies heated to different temperatures emit light from an unequal wavelength. The color determined by the human eye depends on this parameter. The shorter the wavelength, the hotter the body and the closer its color to white and blue. This is true for stars.
Red luminaries are the coldest. The temperature of their surface reaches only 3 thousand degrees. A yellow star, like our Sun, is already hotter. Her photosphere heats up to 6000º. White luminaries are even more red-hot - from 10 to 20 thousand degrees. And finally, the blue stars are the hottest. The temperature of their surface reaches from 30 to 100 thousand degrees.
General characteristics
Yellow stars, the names of many of which are well known to people far from astronomy, have been discovered by scientists in large numbers. They differ in size, mass, luminosity and some other characteristics. The common thing for such luminaries is precisely the surface temperature.
The luminosity can acquire yellow color in the process of evolution. However, the vast majority of such stars are located on the Main sequence of the Hertzsprung-Russell diagram. These are the so-called yellow dwarfs, which include the Sun.
The main star of the system
Such luminaries are called dwarfs because of their relatively small size. The diameter of the Sun on average is 1.39 * 10 9 m, mass - 1.99 * 10 30 kg. Both parameters significantly exceed the similar characteristics of the Earth, however, in outer space they are not something out of the ordinary. There are other yellow stars, examples of which are given below, significantly ahead of the Sun in size.
The surface temperature of our luminary reaches 6 thousand Kelvin. The sun belongs to the spectral class G2V. In fact, it emits almost pure white light, however, due to the nature of the planet’s atmosphere, the short-wavelength part of the spectrum is absorbed. As a result, a yellow tint appears .
Features of the Yellow Dwarf
Small luminaries are characterized by an impressive life expectancy. The average value of this parameter is 10 billion years. The sun is now located approximately in the middle of the life cycle, that is, until it leaves the Main sequence and turns into a red giant, it remains about 5 billion years.
The star, yellow and belonging to the type of “dwarfs", has dimensions similar to those of the sun. The energy source of such luminaries is the synthesis of helium from hydrogen. They proceed to the next stage of evolution after hydrogen ends in the nucleus and the burning of helium begins.
In addition to the Sun, yellow dwarfs include Alpha Centauri A, Alpha of the Northern Crown, Mu Bootes, Tau Ceti and other luminaries.
Yellow subgiants
Stars similar to the Sun, after the exhaustion of hydrogen fuel, begin to change. When helium is lit in the core, the luminosity will expand and turn into a red giant. However, this stage does not occur immediately. First, the outer layers begin to burn. The star has already left the Main sequence, but has not yet expanded - it is at the sub-giant stage. The mass of such a luminary usually varies from 1 to 5 solar masses.
The stage of the yellow subgiant can also go through more impressive stars. However, for them this stage is less pronounced. The most famous subgiant today is Procyon (Alpha Lesser Dog).
True rarity
The yellow stars, the names of which are given above, are quite common in the Universe types. Otherwise, the situation with hypergiants. These are real giants, considered the most difficult, brightest and largest and at the same time possessing the shortest life expectancy. Most well-known hypergiants are bright blue variables, however, among them are white, yellow stars and even red ones.
Such rare cosmic bodies include, for example, Ro Cassiopeia. This is a yellow hypergiant, luminosity 550 thousand times ahead of the Sun. It is 12,000 light-years distant from our planet . On a clear night it can be seen with the naked eye (visible gloss - 4.52m).
Supergiants
Hypergiants are a special case of supergiants. The latter also include yellow stars. They, according to astronomers, are a transitional stage in the evolution of luminaries from blue to red supergiant. Nevertheless, in the stage of the yellow supergiant, the star can exist for a long time. As a rule, at this stage of evolution, luminaries do not perish. For all the time of studying outer space, only two supernovae, generated by yellow supergiants, were recorded.
Such luminaries include Canopus (Alpha Kiel), Rastaban (Beta Dragon), Beta Aquarius and some other objects.
As you can see, each star, yellow like the Sun, has specific characteristics. However, everyone has something in common - this is the color that is the result of heating the photosphere to certain temperatures. In addition to these, such luminaries include Epsilon Shield and Beta Raven (bright giants), the Delta of the Southern Triangle and Beta Giraffe (supergiants), Capella and Vindemiatrix (giants), and many other cosmic bodies. It should be noted that the color indicated in the classification of the object does not always coincide with the visible. This happens because the true shade of light is distorted due to gas and dust, as well as after passing through the atmosphere. A spectrograph apparatus is used to determine the color of astrophysicists: it provides much more accurate information than the human eye. It is thanks to him that scientists can distinguish between blue, yellow and red stars, remote from us over great distances.