The Pinwheel galaxy (M101, NGC 5457, Arp 26, Uppsala 8981, MCG 9-23-28, PGC 50063) is very famous in photographs, with its classic and nearly perfect spiral arms seen face on. Its distance of about 10 million light years accounts for how large and bright this spiral galaxy appears. Visible even in binoculars from a dark site this galaxy can nonetheless prove difficult to find.
Although quite bright, M101 has a very low surface brightness and is a classic example of how difficult it can be observe such objects. The integrated magnitude of M101 is a bright 8.2, and if it were all concentrated into a star, M101 would be a piece of cake. But instead all that light is spread out over a circular area roughly 30' in diameter.
I'm convinced that this is the most difficult of the Messier objects. My search for M101 began over two decades ago as I scoured my "Atlas of the Heavens" for objects to view in my newly acquired 6" telescope. A bright Messier galaxy that made an equilateral triangle with the two stars at the end of the handle of the Big Dipper seemed like an easy target. But try as I might, I couldn't find it. Over the years I searched again and again (somewhat half-heartedly) with all sorts of instruments, from binoculars to a 21-inch telescope. Always to no avail.
After 20 years of searching I found myself at Mount Laguna, about 50 miles east of San Diego. It was March of 1996, and we were blessed with one of those once-in-a-lifetime nights with crystal clear air and a velvety-black sky. Stretching some 50 degrees overhead was the most amazing comet I had ever seen. I followed Hyakutake's magnificent tail in my 8 x 56 binoculars, looking for knots or other structures. Right there, embedded in the tail, was this small, round smudge. I wondered aloud what it was... after all I didn't know of any bright galaxies in that area. Was it part of the tail? The comet moved during the next few hours, but my smudge did not. With a sudden flash of insight I realized what it was--I had finally found M 101!
The funny thing is that ever since I've had little trouble finding it. Knowing what to look for is a big part of the battle. How large is it? How diffuse? Exactly where should I look? That's where really good charts can come in--something I didn't have until more recently.
In smaller instruments, or even at first glance in larger ones, you will see only the brighter inner portion of the Pinwheel--something that often leads to confusion because people expect it to be much larger (as often plotted on charts). For starters, look for a small hazy ball about 5' in diameter. Once found, look for the beginnings of the spiral arms as stubs emanating from the round ball. Observers with larger instruments (> 10") may see knots of bright stars and nebulae that trace the spiral arms much further away from the center. In my 18-inch Dob with averted vision I've been able to clearly make out the spiral pattern, nearly filling the 19' field of view in a 12.4mm Super Plossl.
Millennium Star Atlas Vol II Chart 570 Sky Atlas 2000 Chart 2 Uranometria 2000 Vol I Chart 49
This is a simulated view of the field in a 6-inch at 50x.