Pierre Méchain discovered M101 = NGC 5457 = h1744 on 27 Mar 1781. On 14 Apr 1789 (sweep 921), William Herschel described "a very bright small nucleus with extensive nebulosity, pretty well determined on the preceding side, but very diffuse to the north following. Includes the two following nebulae [III-788 = NGC 5461 and III-789 = NGC 5462], and seems to extend 20', perhaps 30' or more."

Bindon Stoney (LdR's assistant) sketched the various HII knots, spiral arms and superimposed stars and measured offsets in 1851. Samuel Hunter's superb sketch from 29 Apr 1861 was included at the last minute in the 1861 publication. This is probably the finest and most accurate sketch of a spiral galaxy done at Birr Castle and is very favorably compared with the DSS.

M101 has had 4 supernovae, the first (SN 1909A) was discovered by Max Wolf. It was announced as a variable star in Feb 1909 and assigned the designation SS UMa. The others are SN 1951H, SN 1970G and Type Ia SN 2011fe, which reached mag 10.9.

300/350mm - 13.1" (6/4/84): four HII regions resolved including NGC 5447, NGC 5458, NGC 5461, NGC 5462.

13.1" (4/24/82): fairly bright, very large, round, about 20' diameter, bright core. Fairly low surface brightness but beautifully resolved into several distinct arms and sections of arms with a pinwheel design. Obvious mottling along the spiral arms which appear clumpy with two or more easily recognized HII regions. At least six stars are superimposed.

400/500mm - 18" (6/21/03 and 6/28/03): the following HII regions were observed --

NGC 5447: at 215x this fairly prominent HII region appeared as an elongated patch oriented NNW-SSE, perhaps 25"x8", located just south of a mag 13.5 star. At 323x this patch clearly resolved into two sections -- within 30" of the star is a very compact knot, ~6"-10" diameter. There may be a small gap to the south with a larger extension to the SSE (this is NGC 5450). Located on the opposite side of M101 as NGC 5462.

NGC 5449: marginal object at 323x, but backing down to 215x a weak but definite glow was visible, perhaps 15"-20" diameter. Located 3.5' N of NGC 5457. NGC 5450: just resolved from NGC 5447 at 323x and was an elongated patch oriented NNW-SSE, ~20"x6". The entire complex spans ~45".

NGC 5451: very difficult, low surface brightness glow, ~10"-15" in size, requiring averted vision to glimpse. More difficult than two mag 15.5 stars separated by 13", which are location 1' WSW. The combined glow of these stars could easily mislead the observer into logging these as NGC 5451! In fact on 6/21/03 I initially picked up a small, hazy glow nearly collinear with a mag 12.9 star just north of the core of M101 and a slightly fainter star due west. But in good moments, this very small glow resolved into two stellar objects, probably appearing slightly hazy due to the background glow of the outer halo. After a more careful view, I noticed an extremely faint knot with averted vision, ~15" diameter, located ~2' ENE of this pair -- this is NGC 5451.

NGC 5453: required averted and concentration to confirm a small, low surface brightness glow, just visible over the background glow of the spiral arm this HII region resides. In fact, between NGC 5453 and the core is an inner arm which contains a couple of HII knots which are more evident!

Anon knot: two small, low contrast knots are visible in the spiral arm that is attached on the west side of the core of M101 and wraps around the south side towards the east. These are situated just 1.7' SW of the center of M101. Although this knotty structure does not have a NGC number it is slightly more evident than a few of the faintest NGC HII regions.

NGC 5455: compact knot, round, easily identified as forms the southern vertex of a triangle with two 13th magnitude stars to the NW and NE. At moments, a stellar nucleus or superimposed star pops out at 323x.

NGC 5458: very faint glow 3' S of the core of M101 on a line between a 13th magnitude star ~7' S of the center of M101. Requires averted for a definite sighting and appears to have a low, even surface brightness, ~20" diameter. Easier to view than NGC 5453.

NGC 5461: at 435x (5.2mm Pentax) a fairly bright quasi-stellar knot is attached at the NE end with a relatively faint extension (even surface brightness) extending to the SW. On 6/21 at 215x, this prominent HII region has a high surface brightness and stands out well. Increasing the power to 435x, there is a stellar or quasi-stellar core offset at the NE end with a faint extension to the SW. Backing down to 323x and using a UHC filter, the glow decreases in size, but the star-like core seems to increase slightly in contrast. NGC 5462: this HII region is probably the largest continuous piece. It appears very elongated 3:1 or 7:2 SW-NE, roughly 60"x18". On 6/21 appeared fairly bright and relatively large, elongated 3:1, ~50"x17" SW-NE. This HII region has an irregular surface brightness with a bright, nearly stellar knot at the NE end.

NGC 5471: highest surface brightness of any of the HII regions in M101. Appears very similar to a small, elliptical galaxy -- even contains a small, brighter core. Situated beyond the main glow of the galaxy, 11.5' NE of the core of M101. On 6/21 at 323x appears similar to a compact, round galaxy. Furthest NE of all the HII regions and well separated from the main glow of M101. Interestingly, this was one of the few HII regions that did show a positive contrast response to a UHC filter at 161x and 215x.

600/800mm - 24" (5/24/20): at 375x; I identified all visible HII regions and stellar associations in M101, 10 of which have NGC designations (5447, 5449, 5450, 5451, 5453, 5455, 5458, 5461, 5462 and 5471). In addition, I logged 4 additional low contrast knots from Banich's 2013 article in Sky & Telescope.

Notes by Steve Gottlieb