Cluster ’round, Star Splitters, and return with me to the land of the mythical Unicorn!
In our last episode we followed the vertical allure of a line of right ascensional bliss — a line which led to yours truly being stunned into a stupor by the scintillating blue and white photons of the beautiful Beta (β) Monocerotis. If you can remember back to that episode of Monocerosic meanderings, we followed the charming and mysterious RA line at 06h and 26.7m to a veritable feast of photonic pleasures.
So come with me once again as we ascend another line of right ascension in search of double star delights. This time we shall seek out those which have succumbed to the grasping gravitational influences of ……… Monocerotic clusters.
Line yourself up now at a blissful 06h and 28m, dial your declination to -07° 02′ ……… and follow me into the nebulous darkness.
And as you can see, we’re going to start with the beautiful Beta (β) Monocerotis because ………. because ………. well —- just because we are.
But take your time here.
Absorb the blue and white photons of pure pleasure from these three delightful orbs of lovely light.
Let your eyes linger.
Permit the rays of blue-white light to penetrate deeply into the inner recesses of your unconscious star dusted mental machinery. Enjoy those voluptuous high voltage vibrations as they select and activate the synaptical electrical pathways that will slowly stun you into a semi-permanent stupor.
Oh — and don’t let go of the arm of your chair, either.
Now ………… let’s see if we can slip the chains of this stupor and dial up our next declinational destination: -04° 46′. I’ll give you a few minutes to let out that long lung rattling sigh and loosen your grip on the chair’s arm.
10 Monocerotis (BUP 89) (AB is H V 14) HIP: 30772 SAO: 133290
RA: 06h 28m Dec: -04° 46′
Magnitudes: AB: 5.1, 9.2 AC: 5.1, 9.2
Separation AB: 77.0″ AC: 78.0″
Position Angle AB: 257° (WDS 2002) AC: 232° (WDS 2004)
Distance: 1354 Light Years
Stellar Classification: B2, B2
Now if you haven’t succumbed to the subtle hint to put those neglected old fashioned setting circles into use, take a look in your finder while Beta (β) Monocerotis is centered in it and you should see 10 Monocerotis about two and a half degrees to the north of it.
And what we have here is a triple star smack dab in the middle of an open cluster, NGC 2232. Kind of hard to upstage the blinding light of that last view, but this isn’t a bad start.
NGC 2232 is a rather loose cluster of stars split into two groups, one of which is the collection of stars to the east of the primary as shown in the sketch here. Our targeted triple stands out rather well here because the “B” and “C” stars are of equal magnitude and essentially the same distance from the primary. In fact, when I first feasted my eyes on this pair of stars, I thought they looked as if they were put there deliberately. I suspect only the Unicorn knows for sure, but since its form of communication is mainly mythical, we’ll probably never know.
In the Meade AR-5 I was using when I made the sketch, the primary struck me as white with a tinge of yellow in it. My guess is the yellow had more to do with it’s low position in the southwest than with the star’s actual color. But despite the low location, I could detect just a bit of nebulosity hovering in the background.
I keep an f/13.3 60mm Lafayette refractor mounted on my AR-5, so I took a peek in the 20mm TV Plössl (40x) that I had presciently placed in it and had to activate my averted vision to see the two faint companions of the 5.1 magnitude primary. Considering the 4.1 magnitudes of difference at work here, I wasn’t taken by surprise. That difference translates into “B” and “C” being 40 times fainter than “A” — just enough to present a healthy challenge for an aspiring — or an experienced — Star Splitter’s eyes.
That “BUP 89” which is in parenthesis in the data line above is a reference to “Burnham’s 1913 proper motion catalog,” the actual title of which is A General Catalogue of 1290 Double Stars Discovered from 1871 to 1899 by S. W. Burnham. I included it here mainly because if you search the Washington Double Star Catalog for 10 Monocerotis, you’ll find it listed only with that designation.
But — this isn’t the well known Robert Burnham, Jr., of Burnhams Celstial Handbook fame. Nope — this is Sherburne Wesley Burnham (1838-1921), who discovered over 1500 double stars (many with a six inch Clark refractor), some of which displayed orbital motion — and there you have the connection to the “1913 proper motion catalog.” I was able to dig that little morsel of information out of the Webb Society Deep-Sky Observer’s Handbook, Volume 1: Double Stars, second edition, pp. 65 and 66. It also mentions on page 65 that near the beginning of his amateur activity in 1866, he “was changing telescopes regularly, never being satisfied with his current acquisition.”
…………. And so now we know who started THAT obsession! 😉
OK — now nudge your scope from the negative side of its declination circle to the positive side and let it come to rest at our next Monocerotic coordinate, +05° 16 m ….. and don’t touch that RA circle! Or you’ll end up who knows where — possibly hiding in Hydra or lost over in Orion.
OR — if you have neglected to become involved in this setting circle exercise, hop your way up to Epsilon (ε) Monocerotis using the second or third chart above, and then switch to the chart below to HIP and hop past the pair of Hipparchus numbered stars to the northeast of Epsilon (ε). You’ll find Σ 915 barely to the northeast of the second one, 6.7 magnitude HIP 30375.
Σ 915 HIP: 30793 SAO: 113926
RA: 06h 28.2m Dec: +05° 16′
Magnitudes: 7.6, 8.5
Position Angle: 42° (WDS 2007)
Distance: 1289 Light Years
Stellar Classification: A1
Up in this area we’re under the influence of the beautiful Rosette nebula, which is just over at the east edge of your eyepiece. We’ll come back to that shortly, but if you see wisps of nebula in your eyepiece, don’t panic. It’s not smoke, and your visual apparatus is still functioning normally.
This one is located in an area with a somewhat dense population of stars. However, it still stands out from the star field because it’s surrounded by a small void of black space which shows up reasonably well in the photo below, and is even more obvious in the eyepiece.
Now I’ll let you in on a little secret. I got lost here. And it’s because I made a rather stupid mistake for an experienced Star Splitter. I marked the locations of Σ 915 and Σ 926 in my Sky &Telescope Pocket Atlas, and for reasons totally beyond my comprehension ….. I reversed them. Which should not be a big deal, because there are still double stars at both locations …… except that I was looking for a secondary at 287 degrees when I should have been looking for it at 42 degrees. After about twenty minutes of fruitless searching and Monocerosic mutterings, I finally figured it out. My purpose here is not to impress you with the fact that I can be humble ( 😉 ), but that anyone can make a mindless mistake no matter how long they’ve been at this. Sometimes it seems that Frustration and Photons wrestle over which one will rule the night — so consider yourself warned!
And it didn’t help that the secondary of this one is only six arc seconds from the primary. That’s closer than it sounds when you’re searching at a low magnification. In fact, you can skip right over it numerous times without any effort at all. I did.
But it’s there — you just have to look very carefully.
In my AR-5 this was a very close pair in a 20mm TV Plössl (59x). My favorite “wide field” eyepiece, an 18mm Radian (66x), gave me a clean split (a bit wider than the hairline split shown in the chart at that link), but the two stars were still perilously close in proximity to each other. In fact, so close to each other that I couldn’t pry them apart in my 60mm scope. I tried twice — once with a 15mm TV Plössl (53x) and again with a 12mm Brandon (67x), but the glare of the primary proved to be too much on this night. It should be possible, however, under better conditions.
As far as color, I thought I saw a slight bit of yellow in the primary, but I couldn’t be sure. I think the low altitude was once again luring my eyes toward yellow.
Our next move is to the north side of the Rosette Nebula. If you’re using setting circles, slowly slide 30′ north to a position of +05° 46′. Then, we’re going to abandon the trusty RA position of 06h 28m which has led us to such success and move 3.7 minutes east to 06h 31.7m — feel free to round that off to 32m and you should succeed sufficiently.
For you Star Hoppers out there, go back to the last chart, and you’ll see a triangle of seventh magnitude stars to the northeast of Σ 915. With Σ 915 still visible in the eyepiece of your scope, take a peek in your finder and you should have no problem seeing that stellar triangle hovering north of the cluster of stars that mark the location of the Rosette Nebula. The one you want is the most southern of the three, or put it another way, the one at the north edge of the Rosette.
Either way — setting circles or star hopping — move carefully or you’ll find yourself drawn into the center of the Rosette by the powerful pull of its mysterious magical clouds of nebulosity. I got lost in there one night and it took me an hour to find my way out.
Σ 926 (H III 75) HIP: 31110 SAO: 114003
RA: 06h 31.7m Dec: +05° 46′
Magnitudes: 7.2, 8.6
Position Angle: 288° (WDS 2007)
Distance: 190 Light Years (approximate)
Stellar Classification: A1
Now as you can see in the sketch at the right, there are a lot of stars in this field. And there’s a reason for that. We’ve landed in the southeast corner of another open cluster, this one being Collinder 97.
The “A” and “B” components of Σ 926 are shown to the right of center in the sketch at the right, and the other two stars of our locating triangle are also shown at the west and north edges. What really caught my eye here is the almost asterism of stars which stretches out to the southeast of Σ 926, and the similarly shaped group spread out more thinly on the opposite, northwest side of it. The pattern on the southeast side resembles the “V” of the Hyades cluster, and the one on the opposite side is a more open version of the same thing. In the 20mm TV Plössl I used for the sketch, many of those stars are faint, requiring a careful focus and a hard look.
This is a wider pair of stars than Σ 915, and it stands out well in this field because of it’s brightness. Unlike the difficulty I had with Σ 915 in my 60mm scope, this one was easy to split with the 15mm TV Plössl (53x). And of course it was no problem in the AR-5. The primary is a pale version of white, and there are hints of nebulosity strewn throughout the field as well. In fact, when I removed the 20mm TV Plössl that I used for the sketch and replaced it with a 12mm Brandon (98x), the nebulosity was really noticeable. I put the 20mm eyepiece back into the diagonal and found if I looked very closely, I could see quite a bit of it — I had missed it the first time because it was much fainter in the 20mm.
So it’s worth the time and effort to peer deeply into this area. And it always amazes me what you can miss even when you do look long and hard — and what you can see in a later observation once you know where and how to look for it. Those italicized words may strike you as strange, but if you keep at this long enough and frequently enough, you’ll see what I mean. Even experienced observers often find themselves surprised at what they’ve missed in previous observations.
So our Monocerotic meanderings come to another close ……. and there is a possibility that a third adventure will materialize in cyberspace soon, provided the weather cooperates.
But — as long as you’re in the area, don’t hesitate to let your scope drop a very slight distance to the south and saturate it’s lens (or mirror) with the starlight of that open cluster, NGC 2244, that marks the Rosette Nebula. The cluster is easy to see — the nebula which surrounds it may take a bit of work. If you have dark skies, it should begin to emerge if you look closely — try moving your scope back and forth just a slight bit and you should begin to see hints of it start to appear. It’s especially dense on the west side of the cluster. (If you’re new to this, the nebulosity will not appear red, as shown in the chart or in photographs — for that, you need the eyes of a bat!)
And if you have an OIII filter, put it to work right away. It will transform this area into a glowing pale gray cloud with more nebulous knots and twisting tendrils in it than a piece of chocolate cake with streaks of white icing laced through it.
Which reminds me, tea and desert are waiting!