red giant and supergiant - is the name of space objects with extended shells and high luminosity.They belong to the late spectral classes K and M. These solar radii exceed a hundred times.The maximum radiation of the star falls on the red and infrared region of the spectrum.On the Hertzsprung - Russell red giants are located above the line of the main sequence, their absolute magnitude varies from just above zero or a negative value.
area of such a star exceeds the area of the sun for at least 1,500 times, while its diameter is approximately 40 times greater.Since the difference in absolute value with our luminary is about five, it appears that emits a red giant a hundred times more light.But he is much colder.Solar temperature twice the performance of a red giant, and therefore per unit of surface area of the light of our system emits light at sixteen times more.
The apparent color of the star depends on the surface temperature.Our sun is heated until white and has a relatively small size, so it is called yellow dwarf.Cooler stars are orange and red light.Each star in the course of its evolution could reach the last spectral classes and become a red giant in two stages of development.This occurs during the nucleation step star or at the final stage of evolution.At this time, a red giant begins to radiate energy through its own gravitational energy released when compressed.
As the star is compressed, its temperature rises.Thus, due to downsizing of the surface, at times falling luminosity.She dies.If it is a "young" red giant, it will eventually run its subsoil reaction of thermonuclear fusion of hydrogen helium.After that the young star will enter the main sequence.The old star a different fate.In the later stages of the evolution of hydrogen in the interior lights fade completely.Then the star leaves the main sequence.According to the Hertzsprung - Russell, she moves to the red supergiants and giants.But before you go on the stage, it passes an intermediate step - subgiant.
subgiants called stars in the nucleus of which has stopped hydrogen fusion reactions, but the burning of helium has not yet begun.This is because the core warmed up enough.An example of this can be subgiant Arthur, located in the constellation Bootes.It is an orange star with an apparent magnitude of -0.1.It is located at a distance from the sun is about 36 - 38 light years.You can watch it in the northern hemisphere in May, if you look directly at the south.Arthur diameter 40 times solar.
yellow dwarf sun is a relatively young star.Its age is estimated to be 4.57 billion years old.In the main sequence, it will remain still about 5 billion years.But the scientists were able to simulate the world in which the sun - a red giant.Its size will grow to 200 times and reached Earth's orbit, incinerating Mercury and Venus.Of course, life at this time will be impossible.At this stage, the sun will last about another 100 million years, after which it will become a planetary nebula and becomes a white dwarf.
