Any star - yellow, blue or red - is a hot ball of gas. The modern classification of luminaries is based on several parameters. These include surface temperature, size, and brightness. The color of a star seen 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 named below, occupy the middle position on the temperature scale. These luminaries include the Sun.
Differences
Bodies heated to different temperatures emit light with different wavelengths. 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 the stars as well.
Red luminaries are the coldest. Their surface temperature reaches only 3 thousand degrees. The star is yellow, like our Sun, already hot. Its photosphere heats up to 6000º. White luminaries are even hotter - from 10 to 20 thousand degrees. And finally, blue stars are the hottest. The temperature of their surface reaches from 30 to 100 thousand degrees.
General Features
Yellowstars, 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 the surface temperature.
The luminary can acquire a 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.
Main star of the system
Dwarfs such luminaries are called because of their relatively small size. The average diameter of the Sun is 1.39109 m, the mass is 1.991030 kg. Both parameters significantly exceed the similar characteristics of the Earth, but in outer space they are not something out of the ordinary. There are other yellow stars, examples of which are given below, that are significantly larger than the Sun.
The surface temperature of our star reaches 6 thousand Kelvin. The sun belongs to the spectral class G2V. In reality, it emits almost pure white light, however, due to the characteristics of the planet's atmosphere, the short-wavelength part of the spectrum is absorbed. The result is a yellow tint.
Features of a yellow dwarf
Small luminaries are characterized by an impressive lifespan. The average value of this parameter is 10 billion years. The sun is now located approximately in the middle of its life cycle, that isit is about 5 billion years away from leaving the Main Sequence and becoming a red giant.
The star, yellow and of the "dwarf" type, has dimensions similar to those of the sun. The energy source of such luminaries is the synthesis of helium from hydrogen. They move to the next stage of evolution after hydrogen runs out in the core and helium combustion begins.
In addition to the Sun, yellow dwarfs include Alpha Centauri A, Alpha Northern Corona, Mu Bootes, Tau Ceti and other luminaries.
Yellow subgiants
Stars similar to the Sun, after exhausting hydrogen fuel, begin to change. When helium burns in the core, the star will expand and turn into a red giant. However, this stage does not occur immediately. The outer layers begin to burn first. The star has already left the Main Sequence, but has not yet expanded - it is at the subgiant stage. The mass of such a luminary usually varies from 1 to 5 solar masses.
The yellow subgiant stage can also be passed by more impressive stars. However, for them this stage is less pronounced. The most famous subgiant today is Procyon (Alpha Canis Minor).
A real rarity
Yellow stars, the names of which were given above, are quite common types in the Universe. The situation is different with hypergiants. These are real giants, considered the heaviest, brightest and largest and at the same time having the shortest life expectancy. Most known hypergiants are brightblue variables, but there are white, yellow stars and even red stars among them.
The number of such rare cosmic bodies includes, for example, Rho Cassiopeia. This is a yellow hypergiant, 550 thousand times ahead of the Sun in luminosity. It is 12,000 light years away from our planet. On a clear night, it can be seen with the naked eye (visible brilliance is 4.52m).
Supergiants
Hypergiants are a special case of supergiants. The latter also includes yellow stars. They, according to astronomers, are a transitional stage in the evolution of luminaries from blue to red supergiants. Nevertheless, in the stage of a yellow supergiant, a star can exist for quite a long time. As a rule, at this stage of evolution, the luminaries do not die. For all the time of studying outer space, only two supernovae generated by yellow supergiants were recorded.
Such luminaries include Canopus (Alpha Carina), 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 those named, such luminaries include Epsilon Shield and Beta Crow (bright giants), Delta of the Southern Triangle and Beta Giraffe (supergiants), Capella and Vindemiatrix (giants) and many more cosmic bodies. It should be noted that the color indicated in the classification of an object is not alwaysmatches what is visible. This happens because the true color of light is distorted by gas and dust, and also after passing through the atmosphere. Astrophysicists use a spectrograph to determine color: 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, distant from us at great distances.
