Red Giant

Red Giant, large, highly luminous star with a cool surface. They are stars of similar mass to the Sun, or slightly greater, which are swelling up towards the end of their lives—our own Sun will eventually evolve into a red giant, billions of years from now. As the stars swell their surfaces cool to less than 4,000 K (6,740° F), giving rise to their red colour. Red giants are classified as spectral class K and M, the same as red dwarfs, but they have much larger diameters, 20 times that of the Sun or more, and consequently far greater luminosities, many hundreds of times that of the Sun. Many red giants are pulsating variables. Red supergiants are similar in nature to red giants, but have much greater masses and luminosities.