Decorative print of an image taken by the Hubble Telescope. © NASA
Messier 101 (also known as NGC 5457, Pinwheel Galaxy or Firewheel Galaxy) is a spiral galaxy with dimensions of 28.8' × 26.9' and an apparent magnitude of 7.5 in the constellation Ursa Major. It is approximately 22 million light-years away and has a diameter of 170,000 light-years.
Messier 101 was discovered on 27 March 1781 by French astronomer Pierre Méchain. Various bright knots of M 101, which are H II regions, can be found under a separate entry in the NGC.
On 28 February 2006, NASA and ESA published a very impressive image, the largest and most detailed image of a galaxy ever taken with the Hubble Space Telescope. The image was composed of over 51 images.
