This Hubble Space Telescope image shows NGC4639, 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 younger stars. Among them are older variable stars called Cepheids that are used to obtain accurate distances to the galaxies. Astronomers measure the brightness of the Cepheids to compute the distance to a galaxy. The Cepheid's distance result was compared to the distance obtained by studying a type I-A supernova known as 1990-N, located in the same galaxy. They compared those numbers with the peak bright nesses of supernovae seen in nearby galaxies. They determined that type I-A supernovae are reliable secondary distance markers, visible many times farther away than Cepheids. Accurate values of the Hubble constant depend on the Cepheid and secondary distance methods. The color image was formed from separate exposures taken in visible and near Infra Red regions of the spectrum, using the Wide Field Planetary Camera 2.