Open Cluster M67 In Cancer: March 2017 Observer’s Challenge Report

March Observer’s Challenge Report:  Open cluster M67 in Cancer. 


M67 is an open star cluster in the constellation Cancer located 105 arc minutes west of the star Acubens (Alpha Cancri). The cluster is also cataloged as NGC2682. The cluster was first recorded by the German astronomer Johann Gottfried Koehler in 1779 and then by Charles Messier in 1780. The cluster is magnitude 6.1.

M67 has nearly 100 stars between 10th and 14th magnitude spread over a diameter of about 30 arcminutes. The cluster is 2960 light years away and approximately 25 light years across. It is one the closest open clusters and thus one of the most studied. The cluster is several billion (3.2-5) years old. Unlike most star clusters that reside in the plane of the Milky Way, M67 lies 1500 light years away from the plane.

Stellar interactions have flung most of the lighter stars to the outer regions of the cluster, leaving the more massive stars in the center. In possibly 5 billion more years, the cluster will no longer exist as its stars will have spread out too far from one another to be gravitationally bound.

My image of M67 was taken with 190 mm f/5.3 Maksutov-Newtonian telescope with an SBIG ST-2000XCM CCD camera. The exposure was 20 minutes. North is up and east is to the left. The faintest star in the image is 15th magnitude. The exposure captures how the cluster looks in my 14 inch Dob Newtonian.

I viewed the cluster this month with a 6-inch f/6.5 acromatic refractor with a 20mm Nagler eyepiece (50x). The brightest star, shown with the red arrow on my second image, is magnitude 7.8. This star appeared orange to me, but my image does not show that color. That was probably due to my image processing. I captured this image in 2010 and no longer have the original file to check my color processing accuracy.

Three stars stood out at the center of the cluster forming an “L”. I have drawn the L in yellow on the second image. The brightest of the three is magnitude 9.6, while the other two are 10.2. With the 6-inch refractor, I could not visually resolve the half-dozen stars inside of the triangle formed by those three stars. However, the area inside the triangle did not appear as dark as the space between other stars. So my eyes were capturing some of the photons from those unresolved stars.   James Dire – Observer from Hawaii

James M-067-2


Telescope: 6-inch f/6 reflector
Eyepiece: 11mm 82º AF
Sketch Magnification: 83x – FOV: 1.0º

The brightest star of the cluster on the NE tip appears yellow. The cluster is very bright and large, consisting of two sections, the sparse eastern section, and the more concentrated western part. I could count ~ 30 to 40 total stars, with many faint stars being in the background, causing a hazy appearance in these areas. A lane separates the east from the west, traveling north to south, or the entire length of the cluster. With careful and patient observing, several dark lanes were noted.

An almost perfect circle, devoid of stars is obvious in the most concentrated area on the western side.

Inverted pencil sketch:  Roger Ivester 

Rogers M-067a

M67 is a beautiful object.  Two- and three-inch telescopes show a misty patch of light speckled with a few tiny, gleaming stars.  A 6-inch telescope at 120x resolves the cluster into dozens of faint pinpoints, but an overall haze pervades the field of view.  A 10-inch scope at 100x does a better job, because it resolves the group into what is clearly an open star cluster without nebulosity.   
David Eicher 

Image by Mario Motta of Massachusetts using a 6-inch refractor:



This cluster is barely visible to the naked eye as a nebulous patch in the same “field of view” with Praesepe under truly dark skies.  I was observing from Teide National Park, Canary Islands, Spain at an altitude of 7480 feet.  Switching to a pair of 8×30 binoculars the nebulosity stars showing signs of resolution.

With a 4.5 inch Orion SkyQuest XT this is truly a fine cluster even under average observing conditions.  I called M67 “A fine cluster of about 50 stars and many swirling chains of stars”.  At low power there is a faint glow visible in the background slightly concentrated towards the middle.  The core region of the cluster is roughly 12′ in size.  With low power several chains of stars can be seen running NW and SE increasing the cluster’s visual size to nearly 30′ with a bit of imagination.  Foreground 8th magnitude star NE from the cluster appears a “topaz yellow”.  The brightest actual member of M67 is probably magnitude 9.8 TYC 814-1515-1

Two small patches of nebulosity can be discerned within the cluster.  SW one resolved in to 4-5 stars between magnitudes 11-13 with high magnifications. NW one is slightly larger and with high magnification displays a fan-shaped grouping of ~8 stars.   NW section also shows a circular region without stars but this feature is best seen with a larger aperture reminding me of NGC 7789. I could not identify the nearby cluster candidates Chupina 1 or Chupina 2 with the 4.5 inch telescope.  Also I failed to see a specific form in M67 although I commonly see this cluster as an octopus.   Jaakko Saloranta – Observer from Finland 

Jaakko Saloranta: pencil sketch with inverted colors: 



Through my 105 mm refractor at 17x, Alpha Cancri and M67 share the field of view.  This stunning group of many barely resolved and densely packed stars is irregular in both concentration and outline.  A considerably brighter, yellow-orange star adorns its northeastern edge.  At 47x a heavily populated tree of stars dominates the group, its shining trunk and star-leafed branches overspread 11′. At 87x, I count 80 stars in this amazing cluster, which spans about 22′.     Sue French Deep-Sky Wonders – Observer from New York

I observed M67 twice.  My initial observation with a 6” reflector and first ¼ moon in suburban skies revealed a faint compact cluster with about 20 visible stars.  My second observation with a 10” reflector under dark skies showed over 50 cluster members with a prominent notch on one side of the cluster.  Joseph Rothchild –  Observer from Massachusetts

I attempted M67 with 15×70 binoculars from my front yard (LP Bortle
Scale 8). I was able to locate the open cluster, but I was unable to
identify any structure other than a slightly brighter patch with
averted vision. The brightest star of the cluster at the NE tip
resolved amidst the rest of the patch; however, it was not bright
enough to for me to determine a color.   Chris Elledge – Observer from Massachusetts


Date:  January 23, 2017 – Bortle Scale:  3.5: – NELM 5.0 – Telescope:  8-inch SC – Magnification:  92x  

I observed M 67 a number of times in February and March, and was very interested to view it from different angles as it rotated around the NCP.  My first note read “an angel or a bird”; that was my impression based on the shape of the central area of perhaps 250 stars observable with an 8” SCT.  But it definitely didn’t have that form seen setting late on a March evening.  The bright star the AMToB (Amateur Telescope Makes of Boston) has been writing about appears a shade paler than Betelgeuse to me.  This is among my very favorite O.C.s, and I only paid attention to it because of the Observer’s Challenge report!   Craig Sandler Observer from Massachusetts




For some reason, M67 is one of the least observed of the Messiers for me, though I’ve seen it through both my home-built 8-inch f/9.44 back in 1986 in Spain and several times through my home-built 16-inch f/6.4 from various locations.  It’s not by far the champ of least seen Messiers, but not a common object, let’s put it that way.

To complete the Challenge for March, I did my most detailed observation on January 27, 2017 from Furnace Creek in Death Valley at an altitude of -190 feet below sea level. As I’ve probably mentioned before, one would think all that atmosphere would be a hindrance, but that’s not necessarily so. What’s just as important is sky darkness, and almost anywhere in Death Valley is a national dark sky site.

This night, it was cold with occasional gusts, just enough to make it uncomfortable. The skies were clear. Seeing was poor, but transparency was excellent.

At 102X, it was a fairly even mag. bluish clump of about 50 stars with one brighter, slightly orange one off to the side that may or may not be a member. During this observation, I did my best to be more aware of star color, something I’ve strived for given what I’ve learned through the Challenge. In this case, due to seeing, though plenty of stars cut through the muck, extra color wasn’t along for the ride. Not only was it hard to see on this object, but even much brighter ones as well. Last month’s Winter Alberio was another example. It took a lot of strain and looking between waves of boiling sky just to pick out what should’ve been blatant colors on that easy double.

As for M67, while I tried to differentiate other colors, or even just subtle differences, I came away with either the bland gray-blue so common to many clusters, or that one orange one off to the side. Slightly orange as well, because sometimes it blinked more white than orange. Some of the main cluster stars would barely give me blue as well, while once in a while, they’d flash a deeper blue which was much more so than normal.

Note that the drawing blended the mags. a little more homogenous than they actually appeared in the scope. That’s my lack of drawing skills and the pen I was using. The lighter stars, especially the squiggly ones were done in pencil. Also, I omitted a few of the more minor peripheral members on the edge, now that I look at it.    Fred Rayworth – Observer from Nevada


My 70th birthday was March 23. It was low-key – just dinner out with my wife. We’ll be getting together with immediate family for a more formal celebration on Thursday night.  After returning home, I decided to spend a few hours at the ATMoB clubhouse. Because an extended period of cloudy weather was predicted for the upcoming week, I had decided to work on the Double Star Marathon using my 4.5-inch Orion reflector. Steve Clougherty was there with his 18-inch Dob and he was busy with Rich Nugent working on the March and April LVAS Observer’s Challenges!

I spent just enough time to work on the double stars setting in the west (Andromeda, Triangulum, Aries, Eridanus, and Lepus), plus a batch in Orion, then I put things away and observed with Rich and Steve.

While I had been working on the Double Star Marathon, Steve had been busy observing interacting galaxies, NGC 3395-96 in Leo Minor. The pair was faintly visible under magnitude 5 and rapidly hazing up skies.

He then turned to M67. Rich has already sent you a report on what he saw that night. I took a peek and, like Rich, had difficulty noting any obvious coloring of the main stars. I did notice that the cluster seemed to be comprised of two distinct populations – a dozen or so relatively bright members accompanied by several dozen fainter ones.

My first encounter with M67 was on the night of January 11, 1978, when I viewed it with a 3-inch f/10 reflector at 30X. I wrote in my log book, “Faint, ghostly, beautiful; Reminds me of M11. Contains three visible stars attended by a soft glow. Glow bursts into speckles of light with averted vision. General funnel shape.” More recently, I re-observed M67 with the same scope and a higher magnification of 60X. The cluster was better resolved; with a half dozen faint stars surrounded by another dozen or so averted vision stars.   Glenn Chaple – Observer from Massachusetts

Thursday, March 23, 2017:    I was observing with Steve Clougherty at the clubhouse. We were using his 18-inch reflector. The sky was fair (a Bortle Scale 6 or perhaps a little better) but conditions were worsening. By 11 p.m. clouds were overtaking the sky and we ended our observations for the evening.

We decided to take a look at M67. It’s a lovely little cluster but, truth be told, I’ve never found it particularly interesting and have seldom observed it. Thanks for including it in the challenge list because I’ve learned quite a bit about it over the last month! By the way, there’s a nice limiting magnitude chart of M67’s stars on page 69 of this year’s RASC Handbook. I was particularly interested in seeing if it was possible to see the color of some of the cluster’s K-type giant stars. The only color I could see through Steve’s scope was a slight yellow-orange color in HIP 43491 (Spectral type K3) at magnitude ~9.8.

I didn’t pay attention to the nearby, brighter (mag. ~7.9) K0 foreground star (HIP43519/SAO98178) but I will check for color when the skies eventually clear.

Steve and I discussed the value of having an adequate star chart and a capable finder scope when star-hopping to deep sky objects. (We had been searching for April’s challenge: NGC3395/6) I’ll bet when hunting for challenging objects the real challenge isn’t seeing the object as much as it is finding the object! You have to be looking in the right place, right? My favorite print star atlas to have near the telescope is Interstellarum Deep Sky Atlas. This fine atlas shows stars to magnitude 9.5 which is perfect for the 80mm, RACI finders I use on my telescopes. (I use Project Pluto’s Guide v9.0 on my laptop when I need to go deeper.) As experienced star-hoppers well-know, we live and die by our finder system. I use a green laser pointer to roughly aim the scope then acquire the proper star field using the finder. If I can see the desired object in the finder…Bingo! I win. The next best thing to seeing the object itself is seeing the surrounding field stars visible in the atlas. Line the scope with those stars and…Bingo! I win. While I enjoy the chase, I don’t want it to take all night because I really enjoy the view!

As we all have seen, the finder scope that comes with many commercial telescopes is simply inadequate. I try to respectfully implore newbies with such telescopes to upgrade to a “pointer” (Telrad or green laser) and to buy a quality finder scope. It’s all about aperture, right? I decided to run a little test with M67.

Saturday, March 25: 

The sky cleared during the early evening. Temperatures were dropping and surfaces were beginning to freeze over. Framingham enjoys (ahem!) Bortle Scale 7 skies most of the time. I could see Acubens (a cancri; magnitude 4.2) but not much fainter. I could just barely see M44 with my naked eyes but averted vision was necessary. I made a series of observations of M67 (60 degrees in altitude) using 10×21, 8.5×44, 10×50, and 20×80 binoculars. Here are my notes:

10×21: M67 was barely visible; easily missed! HIP43519/SAO98178 was not visible.

8.5×44: A whisper of light; averted vision necessary. HIP43519/SAO98178 was not visible.

10×50: Visible; faint, diffuse; averted vision was helpful. HIP43519/SAO98178 was visible but difficult

20×80: Easy; Obvious! HIP43519/SAO98178 was easily visible.     Richard Nugent – Observer from Massachusetts

M67: ! A beautiful but often-overlooked cluster in the shadow of the Beehive. “Vivid rich type of it exhaulted class.” “Resembles a nebula in small instruments.” “Whorls of stars remind one of a whirlpool.” “Star hues are predominantly rust, orange gold & yellow.”   James Mullaney Observer from Delaware


M67 is very conveniently located about a degree west of Acubens, the alpha star in Cancer, where there’s a lovely little arrangement of four stars in the mag. 4 & 5 range that guide you right to this under-appreciated open cluster. In 7X50 and 10X50 binoculars, the open star cluster is just a fuzzy patch, but in 20X80’s, I could begin to resolve some stars in the center.

In my 4.5-inch Newtonian and my 5-inch refractor at 100X, there were a few dozen or so stars in the eyepiece, and all are in the mag. 10 and 11 range, except for one lone mag. 8 star just to the east of the core.

In my 12.5-inch Newtonian, this cluster became an absolute showpiece! There were easily over 100 stars in the .5° FOV provided by the 12mm eyepiece I was using and the view was simply amazing. It almost makes one wonder why M67 isn’t more celebrated, but it’s probably because you really do need a large scope to bring out the best in this cluster. The view in the smaller scopes was nice, but doesn’t have much wow factor.  Where M44, with its massive size and large population of bright stars really lights up the eyepiece of a small rich-field telescope, the relatively dim M67 doesn’t have much punch. However, put some aperture on it, and stand back! In fact I see M67 as the much better object for a larger scope, because M44 is so huge that it typically doesn’t fit into the smaller field of view provided by bigger scopes, and adding magnification just causes you to lose the “cluster” effect with M44’s spread out population.

I chose to sketch M67 at the eyepiece of my 5-inch refractor. I counted about 40 stars visible in the eyepiece and I didn’t see color in any of them. For comparison purposes, I flipped, cropped and rotated Mario Motta’s image to match the orientation of what I was seeing in the eyepiece. I always find it interesting to compare my drawings to the real deal and see how accurately – or not – my brain and my body transferred what I was seeing onto the paper.  Mike McCabe – Observer from Massachusetts



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