Sorting the Stars by Size

The radius of a star can be determined from the luminosity of the star (which can be determined if the distance is known) and its surface temperature (from its spectral type). It turns out that stars fall into several distinct classes. In sorting the stars by size, astronomers use a vocabulary that sounds as if it came from a fairytale:

• A giant is a star whose radius is between 10 and 100 times that of the sun.
• A supergiant is a star whose radius is more than 100 times that of the sun. Stars of up to 1,000 solar radii are known.
• A dwarf star has a radius similar to or smaller than the sun.