Red giant Red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or lower. The appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but also class S stars and most carbon stars. The most common red giants are stars on the red-giant branch (RGB) that are still fusing hydrogen into helium in a shell surrounding an inert helium core. Other
Sudarsky's gas giant classification to reflection by the cloud decks. At such temperatures, a gas giant may glow red from thermal radiation but the reflected light generally overwhelms thermal radiation. For stars of visual apparent magnitude under 4.50, such planets are theoretically visible to our instruments. Examples of such planets might include 51 Pegasi b and Upsilon Andromedae b. HAT-P-11b and those other extrasolar gas giants found by the Kepler telescope might be possible class V planets, such as Kepler-7b, HAT-P-7b, or Kepler-13 b. Sudarsky's gas giant classification Sudarsky's classification of gas giants for the purpose of predicting their appearance based on their temperature