Star
We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is measured in solar masses (Mʘ). A solar mass is the same as the mass of the Sun. A small star may be about 0.2 Mʘ, a medium one may be about the Sun's mass (1 Mʘ), and a large star may be about 10 Mʘ.