Astronomy Picture of the Week – Distant Spiral Galaxy NGC 4603

This photo taken by the Hubble Space Telescope shows a magnificent view of the spiral galaxy NGC 4603. It is a very distant galaxy because it is located in the Centaurus cluster about 108 million light-years away from Earth.

It is the most distant galaxy in which a special class of pulsating stars called Cepheid variables have been found. About 36-50 of those stars have been observed. Cepheid variables are used as points of reference because their rate of pulsation can be easily calculated. Observing Cepheids so far away helps astronomers to precisely measure the expansion rate of the universe.

Image credit: Jeffrey Newman (Univ. of California at Berkeley) and NASA.