A star will move off the main sequence when it has run out of hydrogen to burn in the fusion reactions. Eventually, the star runs out of helium and other heavier elements to burn, and the thermal pressure is once again overpowered by inward gravitational forces and the star suffers its final collapse and contraction. Many red giants are visible in the sky, even though the red giant phase of stellar evolution is relatively short-lived.
Red giants are some of the most luminous, and largest stars in the universe.
Because they are so bright, we can see them easily in the night sky, even those that are far away. Thus, we are really seeing an exaggerated sample. For example, small, faint, red main sequence stars are more numerous in the galaxy, but they are so faint that we only see the ones that are close to us, and the ones far away are very difficult to detect. Stars with masses greater than about 2.5 - 3.0 M sun . The ultimate fate of our sun is that of a white dwarf .