Gavin James
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M81 - Bode's Galaxy

On New Year's Eve 1774, Johann Elert Bode shunned a night of celebration at one of the parties on offer in his home city of Berlin, in favour of a night of astronomy. 1775 started with great excitement for him as his diligence was rewarded when he found a previously unseen area of nebulosity in Ursa Major to the west of the saucepan. He discovered two galaxies that were to be known as Bode's Nebulae. To him they were nebulous regions within our own Milky Way, but over time it became evident that these nebulae were two far more distant galaxies, great accumulations of stars across the void of space from us here on Earth.

Charles Messier and Pierre Mechain rediscovered Bode's objects in 1779 and added them to their catalogue as M81 and M82. Here we have M81, a spiral galaxy around 12 million light years from Earth with a diameter of about 87,000 light years. Bode’s Galaxy is the largest of the 34 galaxies in the M81 group of galaxies in Ursa Major. The M81 group and our own Local Group, are relatively near neighbours in the Virgo Supercluster. M81's active nucleus is thought to contain a supermassive black hole with a mass of 70 million solar masses. Additionally, M81 is thought to be gravitationally interacting with M82 (The Cigar Galaxy) as M82 has an irregular distorted disk and filamentary-like structures that have been produced around the galaxy because of the stripping of hydrogen by the gravitational pull. There is still significant uncertainty regarding how far away each galaxy is from Earth. This results in a large uncertainty in the distance between the galaxies, with estimates ranging from 100,000 light years to 500,000 light years; consequently it is very difficult to model and determine to what extent they are gravitationally tied.

The galaxy’s blueish tinge, mostly around the edges, has been associated with its starburst characteristic as stars are being formed at a rapid rate. The multitude of pinky red star forming HII regions can easily be seen throughout the galaxy's spiral arms. It is interesting to note that Bode’s Galaxy is very similar to the Milky Way as they both contain approximately the same number of stars, at around 250 billion, and they share a similar spiral shape. Unusually, the rotation curve of M81 falls off with distance in the outer regions of the galaxy, suggesting that M81 does not contain as much dark matter as most galaxies.

On March 28th 1993, a rare type llb supernova - a transitory class between type II and type Ib - was observed in M81 and it became the second brightest supernova event witnessed in the 20th Century. It was designated SN 1933J.

There is one further galaxy worth noting in this image, the faint fuzzy patch just above M81 is the dwarf irregular galaxy UGC 5336, also known as Holmberg IX, named after Erik Holmberg who discovered it. It is a satellite galaxy to M81, similar to the Milky Way's two irregular satellite galaxies, the Large and Small Magellanic Clouds.

Research Assistant: Ben Place




Bode's Galaxy
M81, NGC 3031
Spiral Galaxy
Ursa Major
12 million light years
25 x 12 arcminutes
87,000 light years
1774, Johann Elert Bode
09h 57m 04s
+68º 58’ 30”
Celestron EdgeHD 8" with 0.7x Reducer
8 nights in February 2019
RGB = 18 x 600s each
L = 32 x 1200s
Hα = 14 x 1800s
26 hours 40 minutes


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