The star is a celestial body, it is held by its own gravity and it is estimated that in the Milky Way there are somewhere at 10 ^ 24 stars that can be seen with the naked eye. As a celestial object the star shines due to a thermonuclear energy, where hydrogen is in helium, which are in its nucleus. Theoretically, the star consists of a nebula (molecular cloud to be exact) when it has a gravitational collapse. The star contains hydrogen and helium (71% hydrogen and 27% helium and other smaller chemical components) largely because the nebula also contains these things. According to physicists and physicists who have put their heads to the contribution, we have the following relations of a star: Rated solar brightness: L⊙ = 3.828 × 1026 W; Nominal solar radius R⊙ = 6.957 × 108 m; Nominal solar mass parameter: GM⊙ = 1.3271244 × 10 ^ 20 m ^ 3 s ^ −2. The astronomical constant, as it is called (IAU) has a length of 149,597,870,700 m. Stars die when they run out of fuel. Okay, now there's something more complicated, where you have to know physics. We are talking about the mechanisms of nuclear reactors. Here is used the famous equation of Albert Einstein (physicist): E = mc ^ 2. The process of a hydrogen melting star is so sensitive that any shift in a component can cause disaster. Our core sun has approx. temperature of 10 million K. Below are the equations used for this category of stars.