The Pinwheel Galaxy is in the constellation of Ursa Major and is nearly double the size of our Milky Way with a diameter of about 170,000 light years. The Galaxy sits at a distance of 21 million light years from Earth and is roughly 10 times as far from us as the Andromeda Galaxy.
The Pinwheel Galaxy is the third-largest member of our group of galaxies, which includes the Milky Way, the Andromeda Galaxy, and about 50 other smaller galaxies. It is estimated to contain at least one trillion stars. Approximately 100 billion of these stars could be like our Sun in terms of temperature and lifetime.
The Galaxy’s spiral arms are sprinkled with large regions of star-forming nebulae. Brilliant young clusters of hot, blue, newborn stars trace out the spiral arms. Among the many star formation regions in it’s spiral arms, the giant nebula NGC 604 stands out with a diameter of nearly 1,500 light-years. It stretches over an area 40 times the size of the Orion Nebula.
The light we see from the Pinwheel Galaxy was let out about 21 million years ago. The Galaxy earned its name from its orientation relative to our galaxy, which allows us to observe this spiral galaxy from a face-on perspective.
The Pinwheel Galaxy was discovered by the French astronomer Pierre Méchain on March 27, 1781. Méchain notified Charles Messier of his discovery, and Messier included the galaxy in his catalogue as the 101st object.
On February 28, 2006, NASA and the ESA released a very detailed image of the Pinwheel Galaxy. The image is the largest and most detailed photo of a spiral galaxy ever taken with Hubble, composed from 51 individual exposures, plus some extra ground-based photos.