See my copyright notice for fair use practices. For the Sun, it is the region above the core. Dust clouds in space make stars behind the dust clouds appear redder than they would be if the dust was not there.
Nuclear fusion takes place in a shell around the compressing core.
They are more luminous than when the star was in the main sequence stage, even though their surface is cool, because they have a HUGE surface area. Therefore, they are plotted in the upper right part of the Hertzsprung-Russell diagram . The greater the speed of the object, the greater the redshift will be. It has no size limit and is the type preferred for large research telescopes. The glass lens has a maximum size limit and suffers to some degree from chromatic aberration .