Distance Measurements to a Type-Ia Supernova-Bearing Galaxy

This Hubble Space Telescope image shows NGC 4639, a spiral galaxy located 78 million light-years away in the Virgo cluster of galaxies.

The blue dots in the galaxy's outlying regions indicate the presence of young stars. Among them are young, bright stars called Cepheids, which are used as reliable milepost markers to obtain accurate distances to nearby galaxies.