Astronomy Picture of the Day

Explanation: Here's is a spiral galaxy in true colours. Previously, M81 was shown in two colours only, but M81's real colours are just as dramatic. In the above picture, note how blue the spiral arms are - this indicates the presence of hot young stars and on-going star formation. Also note the yellow hue of the nucleus, indicating am ancient population of stars many billions of years old. M81 is actually a dominant member of a group of galaxies which includes M82 and several other galaxies. Unlike our Local Group of galaxies, large galaxies in the M81 group are actually colliding. It is possible that M81's interaction with M82 create the density waves which generate M81's spiral structure.