The beautiful face-on spiral galaxy M101 in Ursa major is fantastically detailed but dim! It’s only 8th magnitude so it requires long exposures and relatively dark skies.
The images below are composed of 7 x 12 minute (720 sec) and 2 x 6 minute (360 sec) exposures (total integration time = 94 minutes).
M101 has slightly eccentric spiral arms and has many bright nebulae (bright blue-white OB class star clusters and surrounding gas) and reddish HII regions. These features suggest that it has interacted with another galaxy gravitationally and is currently undergoing very active star formation. There are also several background galaxies in the full frame image as a large cluster of galaxies lies in the direction of Ursa major.
Although Charles Messier’s assistant, Pierre Mechain was the first to catalogue M101, It was Lord Rosse in Ireland (with the 72 inch Leviathan telescope at Birr castle) who was the first to analyse and catalogue some of the subregions listed below.
M101 was actually listed twice in the Messier catalogue as M101 and M102 in 1781 (Pierre’s mistake! Corrected in 1783) hence you will sometimes hear the Messier catalogue listed as either 110 or 109 objects.
The individual HII regions and emission nebulae in M101 have their own NGC numbers. M101 has eleven NGC entries – more than any other single entity. I can identify the following 10(the bright blobs within the galaxy):
NGC 5450 HII region
NGC 5451 emission nebula
NGC 5453 emission nebula
NGC 5449 emission nebula
NGC 5447 emission nebula
NGC 5433 emission nebula
NGC 5455 HII region
NGC 5458 emission nebula
NGC 5461 HII region
NGC 5462 HII region
#11 – A bright blue dot just below the galaxy is NGC 5471 which was originally labelled as a “bright nebula” which is observationally correct but Hubble Space Telescope observations have revealed that the glow (pumped by X-ray radiation) is due to the remnants of 3 separate supernovae explosions – again consistent with “recent” intense star formation.
Also visible in the widefield image are:
NGC 5477 spiral galaxy (below M101).
NGC 5473 spiral galaxy
NGC 5474 irregular dwarf galaxy with PGC 4545422 galaxy overlying it (large nebulous area, below and to right of M101).
NGC 5422 spiral galaxy (edge on – like a flying saucer, above and to left of M101).
NGC 5485 spiral galaxy
NGC 5486 spiral galaxy
NGC 5484 elliptical galaxy
Close-up of M101 (click to enlarge).
M101 wide-field view (click to enlarge).
Integration of 2 x 6 minute and 7 x 12 minute exposures (1hr 34 mins total)
480/80mm f6 refractor.1.0 x field flattener. Ioptron ZEQ25GT mount. Guided with Orion SSAG/PHD. modified Canon 60D @ 800ISO with clip-in CLS filter. Acquired with BackyardEOS and post-processed in PixInsight 1.8 and Photoshop CS 3.