Stars and Their Sizes

Part of Scales of the Universe.

Stars and their sizes_HERO AMNH/D. Finnin

Our star, the Sun, is 1.4 million kilometers across. Dim low-mass stars are only a few tenths of that size. The largest stars are luminous red supergiants nearly a thousand times the size of the Sun. Most stars are about the size of the Sun when they are born, and become giant stars in their old age.