Question: How do stars change in brightness

Heidi answered on 14 Nov 2019:

There’s two ways, called intrinsic and extrinsic variability.
Intrinsic variables are stars whose brightness changed because of physical changes – this can be due to pulsations, eruptions or through swelling and shrinking. Extrinsic variables stars are stars that change in brightness because another celestial body has an effect on the star e.g. the star is eclipsed by stellar rotation or by another star or planet.