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Cosmic Challenge: M109

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Cosmic Challenge:



May 2018

Phil Harrington

This month's suggested aperture range:

Giant binoculars & small scopes


2-inch (5cm) and up










11 57.6

+53 22.5

Ursa Major




The galaxy we know today as M109, cross-identified as NGC 3992 in John Dreyer's 1888 New General Catalogue of Nebulae and Clusters of Stars, was first spotted by Messier's contemporary, Pierre Méchain, on March 12, 1781.  He subsequently reported his new find to Messier as "close to Gamma in the Great Bear."  Unfortunately, this was after Messier had submitted his original "Catalogue des Nébuleuses et des Amas d'Étoiles" ("Catalogue of Nebulae and Star Clusters") of 103 objects for publication in the annual French journal of astronomical ephemerides Connoissance des Temps (translated "Knowledge of the Times"). Messier did not live to see a second edition of his catalog, but objects 104 through 110 have been added posthumously by others. M109 joined the ranks in 1953, when astronomy historian Owen Gingerich noted Messier's observations of six additional "Méchain objects," now known as M104 through M109.


Above: Spring star map showing the location of this month's Cosmic Challenge.


Credit: Map adapted from Star Watch by Phil Harrington


Above: Finder chart for this month's Cosmic Challenge.


Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window


Not only is M109's history a little cloudy, spotting it represents one of the toughest challenges in this chapter. Indeed, many a seasoned observer has trouble seeing M109 through far larger telescopes. The low magnifications of binoculars only confound the situation. M109, a nearly face-on barred spiral galaxy, lies just 38' southeast of Phecda [Gamma (γ) Ursae Majoris], the star marking the southeastern corner of the bowl. At magnitude 2.4, Phecda's starlight easily washes out the dim glow of M109 at low power, especially if viewing with less than perfectly clean optics.

That's only part of the problem, however. M109 is one of those objects that, by their nature, have a very low surface brightness. The open structure of M109's spiral disk make it so dim that spotting it through anything smaller than a 6-inch telescope is all but impossible. As a result, smaller instruments reduce M109 to only its central nucleus, which appears as little more than a dim point.


These two facts led the creators of the Astronomical League's Binocular Messier Program to list M109 as a challenge object for an 80-mm binocular. Through my pair of 16x70 binoculars, it only shows up as a dim field "star" with perhaps the slightest hint of fuzziness. Increasing to a 20x80 binocular helps to single out the galaxy from among the few field stars in its immediate area.


The higher magnifications possible through my 4-inch f/10 refractor help to isolate M109's dim glow from the background. At 102x, the galaxy's nucleus appears decidedly lopsided, elongated roughly east-northeast/south-southwest. With averted vision, I can also detect a subtle, somewhat mottled hint of the galaxy's central bar protruding in the same direction, but any trace of the spiral arms that curl away from the ends of that bar remain in the realm of larger apertures and/or more skillful eyes.


While you are in the area, try to spot NGC 3953, another barred spiral set 1.4° due south of Phecda. Some have suggested that Messier may have missed Méchain's reported galaxy and actually saw NGC 3953 instead. Although that conjecture is generally dismissed today, NGC 3953 is often spotted first by observers seeking M109 because of its slightly greater surface brightness.


Above: M109 as sketched through the author's 4-inch (10.2cm) refractor.


Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my web site or post to this month's discussion forum.


Until next month, remember that half of the fun is the thrill of the chase.  Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2018 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


  • CollinofAlabama, Jon Isaacs, okiestarman56 and 2 others like this


Astro Canuck
May 01 2018 07:41 AM

 In July 2012 from my old location and after 13 years I finally saw all the Messier objects with

my C8 from Halifax, and it's light pollution.  M109 was a real challenge, heck M76 was easier as was M97!   I used my 25mm TAL Plossl (80x) eyepiece and kept Phedca just out of the field,

I used adverted vision also had a dark cloth over my head to block other lights about and taped

the telescope a bit.  I was lucky to have a rare clear night here and Ursa Major overhead, but

there it was, a faint smudge in the eyepiece. I took a deep breath, looked away and then back

into the eyepiece, it was still in the same spot. It was to me just a faint grey smudge, never

saw any elongation. I stayed with 80x as it gave a slightly better darker background for me,

anything higher it was lost and in my 40mm Plossl (50x) it made the area too bright. 

    • PhilH likes this

Méchain was really talented at discovering the subtle stuff. If we were to port back to that era... I'll bet we would be frustrated with the equipment (coatings, eyepieces, ergonomics)... but probably Astounded at the sky darkness... even from "populated" sites.  Tom

    • CollinofAlabama, PhilH and jim kuhns like this

Thanks for this months challege Phil!  Great write up and informative narrative about this deep sky wonder.  Going back over my SS notes, I’ve viewed M109, 3 times this year, with my Evo 9.25, 13mm Ethos.  Twice from my home Bortle 7.0 sky’s and once from a somewhat dark sky site.  I noted it as relatively difficult from my home location, and could see the 13.2 mag star located near its center.   Local star of course!  crazy.gif  I also noted NGC3953, as easy to observe when compared to M109.  I also use M109 as a reference object for my home transparency, as it can vary so much during a night of observing.  


Very nice that you could observe it, and sketch such a fine drawing, with your 4 inch refractor!   Clear sky’s.....Peter A.



Thanks once again for your cosmic challenge.  I was able to see m109 in my 80 mm F/6 at 24x , i saw the glow of the body.  At 50x i saw a bit more .  


The area around Phecda is one of my favorites and there some interesting groupings in a large scope. 



    • PhilH likes this

M109 (NGC3992) is classified as an SBbcI-II spiral and is one of the closest galaxies in combined size an structure to the Milky Way.  The mass, rotational velocity, and radius are very close between the two galaxies.  In addition, NGC 3992 is a multi-armed barred spiral like the Milky Way. 

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