Red Giant Stars.

Red Giant Stars Red Giants are very large, cool and luminous stars. This stage lasts about 10% of the stars life. They are old stars meaning they don't have much lifetime left. The red giant phase occurs in stars, which weigh less than 4 solar masses. The star starts to collapse towards the center causing the star to heat up. The fusion rate increases within the outer shells; this causes the star to expand. The surface cools, …

…will lose a lot of mass due to weak gravity at the edge. The outer shells will become unstable causing contractions and variability. The star mass is too small for carbon fusion to occur, so the star collapses. The sun will increase its luminosity by 10,000K. It will cool down to 4,000K and expands 200 radii. When the sun does eventually go through the red giant phase it will end up engulfing mercury, Venus and earth.