M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is seventy percent larger than the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.

M101 is noted for its high population of H II regions, many of which are very large and bright. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. H II regions are ionized by large numbers of extremely bright and hot young stars; those in M101 are capable of creating hot superbubbles. In a 1990 study, 1264 H II regions were cataloged in the galaxy. Three are prominent enough to receive New General Catalogue numbers – NGC 5461, NGC 5462, and NGC 5471.

M101 is a asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong star formation activity in M101’s spiral arms that can be detected in ultraviolet images.

Imaging telescopes or lenses: Ian King Ikharos 8″ RC
Imaging cameras: Atik 314L+
Mounts: Software Bisque Paramount MX
Guiding telescopes or lenses: Orion Mini 50mm Guide Scope
Guiding cameras: QHYCCD QHY5
Software: PixInsight, Software Bisque CCDSoft 5, Software Bisque TheSkyX, iLanga AstroPlanner, Matt Thomas’s CCDCommander
Filters: Baader Luminance 36mm, Baader Red, Green, Blue 36mm
Accessories: Atik EFW2
Dates: March 15, 2013
Frames: 100×300″
Integration: 8.3 hours

Author: Colin McGill
AstroPhotography of the day by SPONLI 04 July 2014