As the outer layers expand into a red giant, what happens to the surface temperature and resulting color?

Answer

The surface cools, shifting emission toward the red end of the spectrum.

As the massive energy output pushes the outer envelopes outward, the energy spreads over a vastly increased surface area, causing the surface temperature to drop and shift the peak emission toward the red end of the visible spectrum.

As the outer layers expand into a red giant, what happens to the surface temperature and resulting color?

#Videos

Why Do Red Giant Stars Get Bigger? - YouTube

astrophysicsred giantstar evolutionmain sequence star