When talk turns to challenging double stars in Cygnus, Delta (δ) Cygni usually comes up quickly in the conversation. It dominates the western wing of Cygnus at a very noticeable magnitude of 2.9, which makes it easy to find. Over on the Swan’s opposite wing, at the very tip, so far out that a powerful flex of those mighty muscles would extend it across the border into Pegasus, is another difficult double, known to admiring Star Splitters as Mu (μ) Cygni. Noticeably dimmer than Delta (δ) Cygni at a visual magnitude of 4.6, it forms a neat little triangular asterism with its two cross-border mates, 14 and 15 Pegasi.
And I’ve been pursuing that little devil for over a month with no success whatever. For a few weeks, people in this little coastal town actually crossed to the other side of the street to avoid hearing my mutterings about Mu (μ).
You see, the problem is the seeing. In fact, it’s not just the seeing, it’s the ocean. Even more in fact, it’s not just the seeing and the ocean, it’s the prevailing wind patterns — which come in off of the ocean most of the time. But eventually all three of those things held a climatic conference and decided to cooperate for a couple of nights. And when they did, I was ready and waiting to finesse that beady little pair of stars out of the inky darkness of interstellar space.
Mu (μ) Cygni (Σ 2822) (H III 15) HIP: 107310 SAO: 89939
RA: 21h 44.1m Dec: +28° 45′
***** Magnitudes Separation Position Angle WDS Data
AB: 4.8, 6.2 1.6″ 318° 2012
AC: 4.8, 11.5 72.6″ 290° 1999
AD: 4.8, 6.9 197.5″ 44° 2011
DE (ES 521) 6.9, 13.3 16.9″ 284° 1999
Stellar Classifications A: F6 B: G2 C: F6 D: F2 E: A5
Distance: 73 Light Years
Status: AB gravitationally linked (orbit can be seen here), AC & AD are optical pairs
My intention had been to bag this one — and by “this one” I mean the AB pair — with my Meade AR-5, a five inch achromatic refractor. Actually, Neil English had called my attention to this star, and was curious about whether I had seen it yet with a five inch scope. I hadn’t, but I quickly put it on my list. However, on that first night of improved seeing, I was sitting behind my six inch f/10 instead. So I swiveled it up and around to the tip of Cygnus’ eastern wing and got to work.
I started with an 18mm Radian (84x), which gave me a great view of both the primary and 6.9 magnitude Mu “D” (which was not at all mu-d like) — but not the first burst of a beam of light from “B”. Not trusting the seeing to hold, I made a quick swap to a 14mm Radian (109x), and was rewarded with my first glimpse of the 6.2 magnitude secondary — an elongated figure-8 image about ready to snap apart. Skipping the 12mm Radian, I grabbed the 10mm version instead (152x), spun the focus knob quickly until the image began to sharpen, then finessed the fine focus knob a bit, and there it was!
Now up to that point I really wasn’t sure what to expect, but I thought it would probably be a very small point of barely visible light. Not at all! What I saw was a rounded little orb of pale yellow-white light about half the diameter of the primary separated by just the slightest slice of silky black night — in all it’s mu-nificence.
After all the times that dot of light had avoided me, I was more thrilled than a telescope addict turned loose at NEAF with fifty thousand dollars of cash in his pocket! It really was just flat out of this world fantastic!
So I had my trusty four-legged side kick hand me the ever dependable 7.5mm Celestron Plössl to see what a 203x view was like — but the seeing was just not quite that good. The split was wider — not by much — but that ir-rhythmic hopping image kind of killed the esthetic attraction on display in the 10mm view. So I slipped that eyepiece back into the diagonal and stared until my visual receptors were saturated.
And then I realized there was something strange taking place in the eyepiece. The color of the primary. There wasn’t one. I mean there was, but I didn’t know what it was. What I mean is — there was more than one. Color, that is.
At first it was white. Unquestionably white. Then it was yellowish. Without a doubt, yellowish. But then, after looking a bit longer, it took on a deep yellow hue. Very yellow, very deep, very definitely. And every now and then, there was just the slightest flash of orange! Just a flash, a very fast flash, but a repetitive flash. And then it was white again. And then back to a weak yellow. I started to wonder about my sanity at this point, which wasn’t helped in the least by the euphonic yipping of the chorusing coyotes in the not very distant distance. Although it didn’t seem to bother my four-legged observing partner in the least.
I had just about decided to chalk this colorful chromatic eyepiece experience up to the euphoric effect of having separated “B” from “A”, when it dawned on me that it might be a good idea to take a look in the 60mm f/15 refractor mounted on the six inch scope. So I stood up, peered into the 20mm TV Plössl (45x) sitting in the diagonal — and saw a sun-yellow primary with a very noticeable orange tint.
So it was back to the books — to see what colors others had seen. Haas didn’t look at it , but she quotes two observers who did: Heckman, who saw a “nice, whitish pair”, and Webb, who saw “Yellow, [with] tawny or blue or lilac.”
Then I went back in time to 1832 to consult with Admiral William H. Smyth, who saw: “A” white, “B”and “D” blue. Then I backed up a little further, to John Herschel and James South’s 1823 observation (Sh 332): “A” white, “B” blue. And finally, even further, to William Herschel’s 1777 observation (H III 15): “A” white, “B” bluish.
Hmmmm — there’s a pattern here, and I’m not in it — nor is Webb.
So I returned to the present to see what the spectral classifications say.
And what they say is the primary is classified as F6, which would be white leaning toward yellow; the secondary is classed as G2, which is yellowish white, leaning a bit more toward the white than the yellow; and “D” is F2, which is more white than the primary, and leaning just a slight bit back toward blue. So I can only conclude that all of us are in the same ball park, but apparently I’m more out in left field than the others are. With the exception of Webb, of course, who is on the other side of the left field foul line with “lilac.”
Now I didn’t try to split “DE” that first night with the six inch f/10 because the seeing was just not that good. The following night, with more stable seeing, I had an AT 111 on the observing deck and was rewarded with another very stirring sight of “B” — so good in fact, that I decided to reach for the “DE” pair. There was quite a bit of haze in the air, so I didn’t expect a lot of luck. But I kept increasing the magnification, and the image was holding reasonably steady, so I worked up to a 3.2mm TMB Planetary eyepiece (243x). I couldn’t quite be sure — I thought I saw something — so I tried the 2.5mm version of that eyepiece, which gave me a seldom seen 311x — and saw nothing but a magnified dark haze.
It was then that the melodius choraling of the coyotes coalesced into a brilliant idea in my Star Splitting subconsciousness — why not put the 7.5mm Celestron Plössl in a 2x Barlow, which would produce 207x? I did. And it produced! With averted vision, I was able to catch the barest glimpse of 13.3 magnitude “E”. I kept looking, and found that occasionally it would become very obvious — still with averted vision, though. I never did see it with direct vision, but then I didn’t really expect to see it at all, so I certainly can’t complain.
Well, I admit to getting giddy again. I even yipped in harmony with the coyotes a few times, just to acknowledge their help. Klaus, my four-legged observing companion, moved to the other side of the deck — I guess to get a better view of his mu-tant master.
Oh, and I’ve neglected to mention 11.5 magnitude “C” — yes, it was easy to see in both large refractors. In fact, it was visible in the 60mm f/15 even at 82x in an 11mm TV Plössl, again with the aid of averted vision.
So to Neil — stellar thanks are due for the suggestion. And, I suppose if I had mu-scled this one into view on the first night, the taste of success wouldn’t have been half as sweet. But as it turned out, sweet hardly comes close to describing my delight.
Cygnus will still be well positioned for the next couple of months to catch this stellar beauty, so don’t dawdle — you absolutely MUST see Mu (μ)!
Clear Skies and decent seeing!