Cepheid stars are stars that have evolved off the main sequence into the Cepheid instability strip. They are regular radial-pulsating stars, with a well-defined period-luminosity relationship, which makes them ideal stars to be used as primary distance indicating standard candles.

Is a Cepheid a bright star or a faint star?

The brightness of a Cepheid variable star changes because the star is actually expanding and contracting in size. ... At its faintest, the variable star Delta Cephei is as dim as the fainter star, Epsilon Cephei.

What is so special about Cepheids?

Cepheids Variables are special type of variable star in that they are hot and massive – five to twenty times as much mass as our Sun – and are known for their tendency to pulsate radially and vary in both diameter and temperature.