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Jewels In Dark Settings, Two By Two
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Spring is not a season that presents a lot of deep sky objects to the irregular chunk of sky I can see from my tree crowded back yard. There are spring galaxies galore, to be sure, but with an average NELM of 4.5 and SQM reading of 18.6, distant galaxies can be a bit unrewarding. A clear, moonless spring night where I live might then seem to be a night of limited opportunities. But springtime being a restless season, something that is as true of amateur astronomers as any member of the kingdom Animalia, I felt an urge to work the sky and find my way to rewarding sights. And so, quite naturally, this backyard session was all about double stars.
It was a beautiful evening from the start, beginning with a perfectly clear sky that ran from pale blue in the low west to about as dark as it gets in Tucson, off over the Rincon Mountains to the east. The brightest stars already burned in the twilight when I went out, including my first target, alpha Geminorum. I’ve looked at and split Castor a number of times, but it’s one of my favorites, so it always manages to end up on the list when the season is right. This time of year, the Twins are standing more or less upright high in the west, making anything within that constellation easy pickings for the Newt. After using Castor to align the 9x50 and Telrad finders (both of which would be put to work tonight) I put in the 21mm Stratus and had a look. At 48x the pair formed a bright, white oblong, like a star that would not quite focus. Castor C was a pale speck to the south-southeast. At 77x the A and B components split cleanly, but the view was much improved by increasing the power to 125x. Two pure white stars of equal (second) magnitude dominated the view, close together, a matching pair of diamonds in the night. I pushed the magnification to 200x, which did nothing to improve the view, but did serve to illustrate that the seeing conditions were pretty good, about 6 on Pickering’s scale. I took a long look at Castor C, trying to detect the “pale lilac” color I’ve seen mentioned regarding this component of the set, but saw only a very faint white star that had something of the quality of frost on a window in winter.
On the list I’d drawn up earlier in the day, delta Geminorum came next. It was no challenge to find, being naked eye visible in the sky by this point. At 48x I saw a whitish star with a bit of warmth to it, but no hint at all that this was a double star. At 77x I could just detect the tiny spark that was the companion star, but 125x brought it into plain sight. The difference in magnitude is large, third magnitude for the main star, eighth for the companion. In terms of color contrast, the bright primary star of the pair looks a touch warmer than pure white to me, lacking the diamond bright purity of Castor, while the companion star shows as a spark of palest blue. These two are pretty close together, all of seven arc seconds apart, and on a night of lesser seeing they might have been a bit of a challenge, even for the Newt. Tonight there was no difficulty in examining both members of this pairing, more evidence that this was a good night to be at the eyepiece.
It was a pleasant evening, weather-wise, into the bargain. Not long after the sun set I found a light sweat jacket comforting, but it never grew chilly enough for more than that. The breeze, when it came, was refreshing and scented by the sweet alyssum growing in the garden beside which I observe. Ah, spring in the desert, when the evening is cool and geckos get frisky. Yes, geckos, several of which were on the wall of the house beside me. They knew it was spring, to judge by the quiet chirps and barks they emitted, and by the general scampering about as they worked out who owned what part of the wall. I have to be careful packing up at the end of a session, this time of year, or I risk bringing one or two into the house with me. There they would become cat toys, a cruel fate indeed. I am very careful to leave my tiny neighbors on their wall, where they belong.
My next target was 38 Geminorum, as star that was just a bit too faint to pick out with my eyes alone. But the Newt and I come well equipped, and so we managed. First I found third magnitude xi Geminorum and using binoculars familiarized myself with the stars around it, and about two degrees to the east. Comparing what I saw to the appropriate B chart in the HB atlas I soon had the position of 38 Geminorum figured out; it was just a matter of pointing the Newt in the right direction. This I did by first sighting on xi Geminorum with the Telrad, which put a good bit of what the binoculars showed into the view of the 9x50 finder, enough to work my way east to what I was convinced was 38 Geminorum. To my delight there was a peanut shaped star near the center of the eyepiece field of view the first time I checked. Increasing the magnification from 48x to 77x cleanly split the components, but it took 125x to really bring the color contrast out for this pair. The primary star was the palest yellow, with the much fainter companion having a subtle hint of blue. This is another fairly close pair (seven arc seconds apart) with a significant difference in magnitude: that of the primary is 4.7, with the companion at magnitude 7.5. Whatever magnification I applied, 38 Geminorum’s location near the edge of the winter Milky Way made for a beautiful and star strewn setting for this pretty pair.
Both finding nu Geminorum (it was naked eye visible) and then splitting it proved no real trouble at all. In fact, it was split by the finder scope! But with a two arc minute separation, that’s not very surprising. The 21mm proved the best eyepiece for this pair, not only showing the bluish-white primary in fine contrast to its bluish, mote-like companion (4.2 vs. 8th magnitude), but bringing into view the pleasing field of stars around them. After two relatively close doubles in a row, this duo almost felt like cheating.
The last double I tracked down in Gemini was 15 Geminorum, a much fainter pair than any I’d gone after so far. Finding it proved easier than I might have expected, using nu and 16 Geminorum as landmarks. In fact, I never needed either finder for this one, and just carefully nudged the Newt in the right direction to bring the desired target into view when I was finished absorbing the sight of nu Geminorum. A magnification of 48x was good enough to split this pair which, while much fainter than my other targets thus far (seventh magnitude primary and ninth magnitude companion), displayed the best yellow/blue color contrast I’d seen up that point. At 77x, as high as I bothered to go, the colors were amazingly clear. Something about the relatively dim magnitudes, combined with the clear color contrast between the components, made them feel incredibly remote compared with the stars I’d been observing up to then. The sense of depth or distance kept me looking for a while. For some reason it caught at my imagination and held me.
By this point in the night Gemini had settled low enough into the west that the low angle was working against the otherwise good seeing conditions. So I left the Twins to their travels, wondering if I’d have a chance to work in that constellation again before these boys are lost in the sun for the season. If not, at least I can rely on their return next year. Sometimes I think the constancy of the stars is a large part of what draws us out into the gentle night with our telescopes.
Iota Cancri is another double star that I’ve observed before, with a pale yellow and cool blue color contrast comparable to that of 15 Geminorum, but involving a much brighter primary star (fourth magnitude) with a sixth magnitude companion separated by about 30 arcseconds. I had no trouble splitting the pair at 48x, but once again a bit of magnification – 77x – served to better bring out the color contrast. It’s a beautiful pair of stars and, like Castor, iota Cancri has for several years been on my list of things worth more than one look.
Having done a couple of open double stars in a row, most of them with significant contrasts in color and magnitude, phi 2 Cancri came as something of a surprise. It took binoculars and both finders to work my way to this pair, which at a combined magnitude of 6 was well beyond naked eye detection. When I found what I thought was the right star, a magnification of 48x showed not a hint of this being a double star. It was oblong at 77x and finally split pretty cleanly at 125x, revealing a set of twin diamonds glittering all of 5 arcseconds apart (according to the reference books crowding my desk). These stars are a matched set, looking absolutely identical to my eye, whichever eye I put to the eyepiece. And there was a silvery quality to their glitter, as if they were somehow a touch metallic, if that makes any sense, or just a bit brighter that white.
Zeta Cancri ended up being the last double for the night, though it was anything but the last one on the list. (I always make the lists a little longer than is truly reasonable.) At 48x this pair was another stellar peanut, but split cleanly when viewed at 77x. The color was also better revealed, and became even more distinct at 125x. These stars appeared yellow to me, plain and simple yellow, and of matching hues as far as I could tell. There was a difference in magnitude, fifth for the primary star and sixth for its companion; nothing dramatic, but quite noticeable. The guidebook I brought out with me (A Visual Atlas of Double Stars by Mike Ropelewski) mentioned a third member, a close companion to the primary star that should be visible to observers with a “sizable instrument.” I’m not sure what the author meant by sizable, but apparently the Newt doesn’t qualify. I pushed the magnification to 200x, but though I thought I could just barely see some elongation in the primary star, it remained a single star. Someday, on a night of truly superb seeing, I’ll “barlow” one eyepiece or another and see what happens. But as good as the seeing was tonight, I was already close to the limit.
If you haven’t felt the allure of double star observing you might find it odd that eight such targets could eat up an evening’s worth of eyepiece time. It’s just stars, after all, two by two. And yet as I came to zeta Cancri I found myself running short on time. It all takes time, of course, especially the part about hunting the sky for a specific target. But there’s something else, something a bit harder to put into words. With double stars, as with any other aspect of visual observing, a timeless quality to the experience takes hold and I can’t hear the minutes ticking by. I find this to be true even through I record the time of each observation I make. It’s as if the times I record are not measures of time’s passage, but static and arbitrary markers of some sort. I can note a specific time on the log sheet, but when I’m at the eyepiece I can’t really feel that time has passed, and so I am usually brought up short at some point by how late it’s gotten to be, no matter how many objects I manage to observe. Each double star (or nebula, or galaxy, or crater) the Newt sends through an eyepiece and into my mind becomes an experience that steps slightly outside of time, and I don’t really know how long I sit there gazing through that little bit of glass. It surely adds up, whether I know it or not, and yet the sum of the experience remains timeless.