M 101 (NGC 5457, Arp 26) Galaxy in Ursa Major

Located at: RA 14 hours 03 minutes 13 seconds, Dec +54 degrees 20 minutes 55 seconds

Size: 28.9' x 26.9' Magnitude: 8.3 blue Class: SAB(rs)cd HII

North is up

West to the right


 8" f5 Newtonian reflector


  ST-8XME, self-guided, binned 1x1, temp -25c, camera control MaxIm DL 4.56


Lumicon Red filter, 710 minutes (71 x 10 minute subs), 04/11/12/14/15/2009; seeing 2.6-4.6 FWHM per CCDStack


CCDStack, Photoshop 7.0


 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)

Notes: This image replaces a 360 minute red filtered image from 05/13/14/2007. I tried doubling the exposure with the new Lumicon red filter, but difference was only marginally more successful. This image is smoother, and processed more realistically, than my previous image. However, the doubling of the exposure time only increased the difficulty of dealing with the gradients. Need a real narrow band filter to significantly increase the contrast/details (i.e., 'pop' the HII regions).

My charting software (Megastar v5.0.13) lists three NGC "knot in Galaxy" designations for brighter areas along M 101's arms, along with NGC 5477 (1.8'x1.3', 14.0v mag, Cl:SA(s)m), the small dim galaxy to the northeast (upper left), and NGC 5471 (0.7'x0.6', -- mag, Cl:-- [NGC / IC Projects identifies this as an HII region]) the small, bright, non-stellar lump midway between M 101's nucleus and NGC 5477. However, the NGC / IC Project lists six other knots with NGC numbers ... There is a lot going on in and around M 101 ...

See the 14.5" version.

From the NGC / IC Project:

Contemporary Visual Observation(s) for NGC 5457
NGC 5457 = M101 = U08981 = MCG +09-23-028 = CGCG 272-021 = Arp 26 = VV 344 = VV 
456 = Pinwheel Galaxy = PGC 50063
14 03 12.4 +54 20 55
V = 7.9;  Size 28.8x26.9;  SB = 14.9

13.1": 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 at least four HII regions resolved 
including N5447, N5458, N5461, N5462.  At least six stars are superimposed.

- by Steve Gottlieb
Historical Research Notes / Correction for NGC 5457
NGC 5457 = Messier 101, and is also Messier 102.  The identification with M102 
has been controversial, however, and rests on a letter that Mechain (who 
discovered M101) wrote to Bernoulli, then the editor of the Berliner Jahrbuch, 
claiming that the object is nothing more than a reobservation of M101.  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

However, some observers are still trying to make the case that M102 is 
actually NGC 5866 (which see).  The evidence points almost unequivocally to 
NGC 5457, but there is some marginal evidence for NGC 5866.  Occam's Razor,
however, points to a simple mistake on Messier's part.

Steve O'Meara's "Eye on the Sky" column in the March 2005 issue of "Sky and
Telescope" has the full story.  There Steve gives his own translation of 
Mechain's letter, and points out that Messier probably mistakenly plotted M102
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. - Dr. Harold G. Corwin, Jr.
** I list observations for only the three knots (and one galaxy?) my software identified ... for the others, see NGC / IC Project ...
Contemporary Visual Observation(s) for NGC 5447**
NGC 5447
14 02 27.9 +54 16 34

18" (6/21/03): 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 N5450).  Located on the opposite 
side of M101 as N5462.

17.5" (6/7/97): brightest HII region on the preceding side of M101 located 7.8' 
SW of center.  Appears as a very elongated glow NW-SE situated just south of a 
mag 13.5 star.  A very small knot is partially resolved at the N edge within a 
common halo with the extension to the SE.  Harold Corwin identifies these two 
components as N5447 and N5450.

13": this is a knot in an outer arm of M101 on the western side.  Easily 
visible, compact, round.  Located symmetrically opposite from N5462 on the 
opposite side of the core.

- by Steve Gottlieb
Historical Research Notes / Correction for NGC 5447/5461/5462/5471
NGC 5447, 5449, 5450, 5451, 5453, 5455, 5458, 5461, 5462, and NGC 5471 are HII
regions and/or star clouds in M 101/M 102.  Most were discovered by LdR, though WH 
found three of the brightest, and d'Arrest noticed the outlier, N5471.  
Unfortunately, only the identifications of WH's and d'A's objects are 

The positions of the others turn out to have been determined by JH for GC.  He
used the sketch of M101 that appeared in LdR's 1861 paper to estimate offsets
from stars with known positions.  This must have been a hurried chore, since
his resulting positions for the knots are not very good.

Without additional observations, Dreyer simply adopted JH's GC positions.
There has thus been some confusion over the identifications of the objects
found by LdR.  Only in two cases, N5461 and N5462 (both found by WH), did LdR
provide offsets from a nearby star.  D'A's object, N5471, not only has a good
position, but is isolated enough from the main body of the galaxy that its
identification is also certain.

To identify the other objects, I have gone back to the published 1861 sketch
where they are clearly shown.  I have easily identified the knots which JH saw
in the same sketch.  With those identifications in hand, I remeasured the 
positions, and have also been able to sort out most of the identifications
used in earlier papers on M101.  The correct identifications and new positions
are in the main Table. - Dr. Harold G. Corwin, Jr.
Contemporary Visual Observation(s) for NGC 5461**
NGC 5461
14 03 40.9 +54 19 02

18" (6/28/03): 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.

18" (6/21/03): 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.

17.5" (6/7/97): fairly faint knot in the trailing arm of M101 4.5' SE of center.  
Appears slightly elongated, ~25"x15", fairly high surface brightness.  Contains 
a very small brighter center or a star is superimposed.

13": this is a knot in M101 located in the spiral arm which trails to the E.  
Appears as a very diffuse, fairly small knot.

- by Steve Gottlieb
Contemporary Visual Observation(s) for NGC 5462**
NGC 5462
14 03 52.9 +54 21 53

18" (6/28/03): this HII region is probably the largest continuous piece.  It 
appears very elongated 3:1 or 7:2 SW-NE, roughly 60"x18".

18" (6/21/03): 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.

17.5" (6/7/97): moderately bright elongated knot in M101, extended 3:1 SW-NE, 
~50"x20".  One of the largest and brightest HII regions in M101.

13": knot in M101 located in the same arm as N5461 but further to the E.  This 
is an easily visible, compact, round knot on the opposite side of the core as 

- by Steve Gottlieb
Contemporary Visual Observation(s) for NGC 5471**
NGC 5471 = MCG +09-23-030
14 04 29.1 +54 23 49
Size 0.9x0.7

18" (6/28/03): 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.

18" (6/21/03): 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.

17.5" (6/7/97): this is one of brightest HII regions in M101, on the extreme NE 
end of the galaxy 11.5' from center.  Appears as a moderately bright knot, ~20" 
diameter.  This HII region stands out well due to its isolation and fairly high 
surface brightness with crisp halo.  Incorrectly identified as a galaxy in MCG.

- by Steve Gottlieb
Contemporary Visual Observation(s) for NGC 5477
NGC 5477 = UGC 09018 = MCG +09-23-034 = CGCG 272-025 = VV 561 = PGC 50262
14 05 32.3 +54 27 33
V = 14.0;  Size 1.7x1.3;  SB = 14.7;  PA = 95d

17.5": extremely faint.  Nearby is a mag 14.5 star 1.2' SW of center and a mag 
15 star is superimposed south of the core.  A brighter mag 12 star is 3.5' E of 
center.  Member of the M101 group.

- by Steve Gottlieb