Stars are the celestial bodies radiating light. They represent huge spheres from gas in which there are thermonuclear reactions. Gas in a star keeps at the expense of gravitational forces. As a rule, stars consist of hydrogen and helium.
Thermonuclear synthesis - a basis of existence of a star
Owing to reactions of thermonuclear synthesis temperature in stars can reach millions of degrees Kelvin - exactly there is a transformation of hydrogen into helium and the huge amount of energy which reaches us in the form of light is distinguished. On a surface of stars temperature decreases on several orders.
Color of stars
From space of a star are visible approximately as well as from the Earth's surface, behind only one exception - the atmosphere of our planet scatters light therefore for the observer who is in an orbit, stars shine brighter. Color of stars at observation from space remains to the same, as well as at observation from Earth, only with a few exceptions. True color of stars at which hydrogen almost "burned out" and temperature about 2000-5000 degrees Kelvin fell, differs from observable. Yellowish-orange stars of spectral class "K" actually have orange color, and orange-red stars of class "M" - red.
Size and form of stars
Stars have very big size. For example, the Sun weighs as much how many 332 thousand planets having the same weight as well as Earth weigh. If to put the mass of all space bodies located in our star system - that their weight in comparison with the mass of the Sun will make percent shares. It is considered to be that the form of stars is constant. But actually it changes. For example, every day diameter of the Sun decreases by two dozen meters. There is also one more interesting fact - it appears, the Sun pulses. With the period of times at 2 hours 40 minutes the surface of a star extends, and then contracts with a speed about seven kilometers per hour. Close the Sun looks as the huge heated sphere on which surface continually there are prominences - emissions of dense substance which keep on a star surface thanks to magnetic field. Not all stars - same big, as the Sun. For example, there are white dwarfs whose size in hundred and more times is less, than diameter of the Sun. At the same time weight them is comparable with a mass of the Sun, just star substance in them is strongly condensed. There are also stars whose diameter can exceed diameter of the Sun in hundreds of times. They are called red giants. There is a theory of life cycle of stars according to which our Sun through several billion years will turn into the red giant too and will increase in a size so that its surface will reach a terrestrial orbit.