M101 is the brightest of a group of at least 9 galaxies, called the M101 Group, which includes M51, the famous Whirlpool Galaxy. The distance to M101 has been determined with the Hubble Space Telescope to be about 24 million light years away and it is about 170,000 light years in diameter.
Of interest are several extremely luminous star-forming (H II) regions in the outer spiral arms, some sporting their own NGC numbers. The clumpy regions and red hydrogen emmison nebulae are esily seen in this photograph.
M101 Spiral Galaxy in Ursa Major (NGC5457)
