NGC/IC Project Restoration Effort

(This is a very very beta version)



Basic Information

Location and Magnitude

Right Ascension: 14:3:12.4
Declination: +54:20:58
Constellation: UMA
Visual Magnitude: 7.9

Historic Information

Discoverer: Mechain
Year of discovery: 1781
Discovery aperture: 3.0


Summary description: pB, vL, iR, g, vsmbMBSN
Sub-type: Sc

Corwin's Notes

===== NGC 5457 = Messier 101, and is perhaps also Messier 102. The identification with M 102 has been controversial, however, and rests on a letter that Mechain (who discovered M 101) wrote to Bernoulli, then the editor of the Berliner Jahrbuch, claiming that the object is nothing more than a mistaken copy of M 101's position. This letter was republished in 1947 by Helen Sawyer Hogg, and is usually taken as proof of the identity. Here is the relevant paragraph extracted from Mechain's letter, first in the original German as published in the Jahrbuch, then in Hogg's English translation: "Seite 267 der Connoissance des tems f. 1784 zeigt Herr Messier unter No. 102 einen Nebelfleck an, den ich zwischen [omicron] Bootes und [iota] Drachen entdeckt habe; dies is aber ein Fehler. Diest Nebel fleck ist mit dem vorhergehenden No. 101 ein und derselbe. Herr Messier hat durch einen Fehler in den Himmelscharten veranlasst, denselben nach dem ihm mitgeheilten Verseichnisse meiner Nebelsterne verwechselt." "On page 267 of the Connaissance des temps for 1784 M. Messier lists under No. 102 a nebula which I have discovered between [omicron] Bootes and [iota] Draconis; this is, however, an error. This nebula is one and the same as the preceding No. 101. M. Messier confused the same as the result of an error in the sky chart, in the list of my nebulous stars communicated to him." (I am grateful to Ashraf Shaker -- at the time he sent it in the mid-1980's -- a student at the Helwan Institute in Egypt, for sending a copy of Hogg's paper "Catalogues of Nebulous Objects in the Eighteenth Century" published in the Journal of the Royal Astronomical Society of Canada, Vol. 41, pp. 265-273, 1947; and reprinted in the Communications from the David Dunlop Observatory, Vol. 1, No. 14. The paper is now -- June 2006 -- available at ADS; the URL is "".) Mechain's letter was pointed to as early as 1877 by Edward Holden in his "Index Catalogue of Books and Memoirs Relating to Nebulae and Clusters." Bigourdan (writing around 1912) also discusses this in the Introduction to his extensive Observations of nebulae and clusters. Steve O'Meara's "Eye on the Sky" column in the March 2005 issue of "Sky and Telescope" has a more complete version of the story that I've abstracted here. There Steve gives his own translation of Mechain's letter, and suggests that Messier mistakenly plotted M 102 east of theta Bootis instead of west, leading to the erroneous description published in the 1781 list. If so, this is far from the only case of an observer confusing directions from a comparison star. Some observers still make a case that M 102 is actually NGC 5866 (which see). The evidence, most recently collected by Michael Covington ("Sky and Telescope", September 2015), is circumstantial -- but hardly less so than asking if Mechain might also have been somehow confused when he claims that M 102 is just a copying error of M 101. What we're missing is any reference to Mechain's original observation as recorded in his log book. Does this still exist? If so, we need to dig it out and look at the observation. Until we have that, Occam's Razor suggests that we take Mechain's letter at face value. So, I am still of the opinion that M 102 is probably identical to M 101. But until definitive evidence can be found, there is clearly no way to be sure just which galaxy it really is.

Steve's Notes

===== NGC 5457 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. 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.