page_title: Messier 81
section_title: Supernovae
hierarchical_section_title: Messier 81 / Supernovae
caption_attribution_description: This is a visible light image of Messier 81 (left) and Messier 82 (right) taken with my backyard telescope in Kalkaska, MI in April of 2007. w:en:Category:Galaxy images
context_page_description: Messier 81 is a grand design spiral galaxy about 12 million light-years away, with a diameter of 90,000 light years, about half the size of the Milky Way, in the constellation Ursa Major. Due to its proximity to Earth, large size, and active galactic nucleus, Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers.
context_section_description: Only one supernova has been detected in Messier 81.  The supernova, named SN 1993J, was discovered on 28 March 1993 by F. García in Spain. At the time, it was the second brightest supernova observed in the 20th century. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernova formed by the explosion of a giant star) with strong hydrogen spectral line emission, but later the hydrogen lines faded and strong helium spectral lines appeared, making the supernova look more like a type Ib.
  Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae, but did resemble the variations observed in type Ib supernovae. Hence, the supernova has been classified as a type IIb, a transitory class between type II and type Ib. The scientific results from this supernova suggested that type Ib and Ic supernovae were formed through the explosions of giant stars through processes similar to those taking place in type II supernovae. Despite the uncertainties in modeling the unusual supernova, it was also used to estimate a very approximate distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81. As a local galaxy, the Central Bureau for Astronomical Telegrams (CBAT) tracks novae in M81 along with M31 and M33.
caption: M81 (left) and M82 (right).  M82 is one of two galaxies strongly influenced gravitationally by M81. The other, NGC 3077, is located off the top edge of this image.
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