Betelgeuse, also called Alpha Orionis, is classified as an M2 supergiant while Aldebaran, also called Alpha Tauri, is a K5 giant star. They differ in luminosity by about 150 times with Aldebaran being the less luminous. However, Aldebaran is still about 200 times more luminous than the Sun! As for their physical sizes, Betelgeuse is about 1300 times the diameter of our Sun and would extend to the orbit of Mars, while Aldebaran is about 30 times larger than the Sun, and extends to nearly the orbit of Mercury.