When a spectral-type G2 star like the Sun leaves the main sequence:

Question

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When a spectral-type G2 star leaves the main sequence, it becomes a red giant or supergiant, and its luminosity increases while its surface temperature decreases. This is due to the star's core running out of hydrogen fuel and contracting, causing an increase in temperature and fusion in the outer layers, leading to a larger radius and increase in luminosity. As the outer layers expand, temperature decreases as the star's energy is spread over a larger surface area.

When a Spectral-Type G2 Star Like the Sun Leaves the Main