1. What is the closest star to earth? This is the Sun. It is located only 150 million km from the Earth, and by space standards is an average star. It is classified as a G2 main sequence yellow dwarf. It has been converting hydrogen to helium for 4.5 billion years now, and will likely continue to do so for another 7 billion years. When the Sun runs out of fuel, it will become a red giant star, the size of the star will increase many times over. As it expands, it will engulf Mercury, Venus, and possibly even the Earth.

2. All stars have the same composition. The birth of a star begins in a cloud of cold molecular hydrogen, which begins to contract gravitationally. When a cloud of molecular hydrogen shrinks in fragments, many of these fragments will form into individual stars. The material gathers into a ball that continues to contract under its own gravity until the center reaches a temperature capable of igniting nuclear fusion. The source gas was formed during the Big Bang and consists of 74% hydrogen and 25% helium. Over time, they convert some of the hydrogen into helium. This is why our Sun is 70% hydrogen and 29% helium. But initially they consist of 3/4 hydrogen and 1/4 helium, with impurities of other trace elements.

3. The stars are in perfect balance. Any star, as it were, is in constant conflict with itself. On the one hand, the entire mass of the star is constantly compressing it with its gravity. But the hot gas exerts enormous pressure from the inside, breaking its gravitational collapse. Nuclear fusion in the core generates a huge amount of energy. Photons, before breaking out, make a journey from the center to the surface, in about 100,000 years. As a star becomes brighter, it expands and becomes a red giant. When the nuclear fusion in the center stops, then nothing can hold back the growing pressure of the overlying layers and it collapses turning into a white dwarf, a neutron star or a black hole. It is possible that the stars in the sky that we see no longer exist, because they are very far away and their light takes billions of years to reach the earth.

4. Most stars are red dwarfs. Comparing all known stars, it can be argued that the most are red dwarfs. They have less than 50% of the mass of the Sun, and red dwarfs can weigh as much as 7.5%. Below this mass, gravitational pressure will not be able to compress the gas at the center to start nuclear fusion. They are called brown dwarfs. Red dwarfs release less than 1/10,000 of the Sun's energy, and can burn for tens of billions of years.