For people living in the northern hemisphere, the famous "W" in Cassiopeia and the big dipper or may be the first star pattern recognized as a child, while for people in the southern hemisphere, the Southern Cross may be the most famous and common. However, these stars are not the brightest!

Every star has its own life cycle. From the moment of its birth, the fate of the star has been doomed. Hydrogen is the most common element in the universe during the formation of each star. The fate of a star depends entirely on the mass of hydrogen contained in it. A star with only 8% of the mass of the sun can still ignite nuclear fusion in its core, fuse hydrogen into helium, and finally transfer the energy to the surface and release it into the universe. These low mass stars are dim red because of their low temperature, and can burn fuel slowly, with a life span of up to trillions of years.

But the greater the mass, the higher the core temperature of the star, and the larger the region where nuclear fusion takes place. When a star reaches the mass of the sun, it is a class G star with a life cycle of only 10 billion years. If the mass is twice that of the sun, it is a class A star with bright blue and a life span of less than 2billion years. If the cores of the most massive stars (class O and class B stars) run out of hydrogen fuel, it will only take a few million years. There is no doubt that heavier, hotter stars are inherently brighter. A typical class A star may be 20 times brighter than the sun, and the largest star may be tens of thousands of times brighter than the sun!

Eventually, for every star, no matter how it starts to glow and heat, its core will run out of hydrogen fuel in a limited time.

When the star runs out of hydrogen fuel, it begins to burn heavier elements and expand into a red giant star, which is cooler but brighter than the original star.