The stars in the universe, is in fact fixed stars, because the planet can't give out light, just like the earth. And fixed star for example the sun, can give out light by oneself.
Each fixed star in the outer space, can all give out light by oneself.
The thin, floating clouds in the space collapse and contract via the gravity, can change the gravity location into the kinetic energy, the increase of the kinetic energy makes the temperature of the thin, floating clouds rise. When rising to 107 K in temperature, make the hydrogen in the thin, floating clouds begin to produce nuclear fusion, release energy.
There are two kinds of hydrogen nuclear fusion course:
Proton - Proton chain (p-p chain)
Carbon nitrogen oxygen circulation (CNO cycle)
Two nuclear fusion course to succeed a piece of helium four hydrogen nuclear fusion, release energy. It produces energy that the main sequence star merges the course with that kind of hydrogen, have close relation with its central temperature. According to the standard model of the sun, the central temperature of the sun is about 15 million degrees, calculate and show, it may be emerging via the proton - the proton chain that the sun is higher than 90% of the energy in theory, it is to come from carbon nitrogen oxygen circulation and is less than 10% (see protons- Proton chain and carbon nitrogen oxygen circulation and relation picture of temperature) . But the fixed star of big quality, the way that energy produces is to take carbon nitrogen oxygen circulation as the core.
It is really too far from the earth because of each fixed star, even a brighter fixed star, we seem it is just a snack, this is the so-called stars.