PC only with location of Cepheids marked

Hubble observed the spiral galaxy NGC 4603, located about 120 million light years away from Earth in the constellation Centaurus. The goal of this observation was to study Cepheid variable stars, of which about 40 were found in the galaxy. The positions of four Cepheid stars are marked on the picture.

Cepheids are 4-20 times more massive than the Sun and 100 000 times more luminous. As their luminosity and pulsation period are connected to each other they are used as to measure the distance of galaxies. Due to their immense luminosity this is possisble out to large distances.