Delta (δ) Cygni (Σ 2579) (H I 94) HIP: 97165 SAO: 48796
RA: 19h 45.0m Dec: 45° 08′
Magnitudes: 2.89, 6.27
Position Angle: 218° (WDS 2013 — orbit can be seen here)
Distance: 171 Light Years
Spectral Classification: B9.5, F1
June 27th, 2010 in the early morning moonlight
OK, so where is it? On this bright, moonlit night, I find myself peering into an 18mm eyepiece (68x) in my six inch refractor and all I can see is one star, not two. I check my notes on this one, and yes, there’s quite a difference in magnitude between the two stars, but I still didn’t expect to have this kind of a “challenge” on my hands. But then, 2.5 arc seconds is pretty darn close, even for a six inch refractor when this much difference exists.
As an aside, if you don’t observe when the moon is out, you’re missing some very pleasant time under the stars. I used to avoid it because for a while I was in search of galaxies, the fainter the better. But after I had seen most every galaxy I could see with an eleven inch SCT, I “discovered” double stars, and although a black sky is ideal for them, you don’t really need it. In the winter time, when the full moon is high overhead, it will limit your ability to see the fainter components, so you just adjust accordingly. But tonight, the almost full moon is low in the south, skirting the tops of the fir trees, and casting some long shadows across my observing deck.
For some reason known only to the weatherman and the full moon, seeing is often pretty darn good under it — no, there’s no scientific explanation for that — and if you haven’t noticed, it seems as if the sky never clears until the moon is full. At any rate, I’ve spent many an enjoyable night under a bright moon, and actually look forward to it. And I tend not to trip over odd things that like to lurk under dark skies.
But, back to the battle at hand. Where’s that other star? I can see the big artillery is going to have to come out for this one, and fortunately, the seeing is pretty steady and Cygnus is nearly overhead. I pick out a 10mm Radian and brace myself — 122x and I think I can see something touching the primary at it’s upper left edge. Hmmm — next move is to reach for a very old 7.5mm Celestron Plossl that is a fantastic little piece of glass — it jumps me up to 163x and we now have a SPLIT!!! But just barely. This just ain’t gonna do. In the house I go and dig out the hardware that seldom gets used in these parts. I pick up a 5mm TMB Planetary eyepiece which has the virtue of being rather inexpensive but deadly, and back to the scope I go with nothing less than complete and total victory planned. The TMB gives me two things – 244x and … and … and … BLACK SKY between the two stars! And now that I can clearly see the two stars, I see why there was a problem — the secondary is barely even a pinpoint of light.
Now, some of you who routinely run your magnification up to 400x or 500x may be chuckling at this, but it’s a rare night on the north coast of Oregon when I can get any higher than 300x and still see a resolvable image that isn’t jumping around so fast it makes your eyes begin to cross. So this is not a minor feat.
But I’m not done yet. I have a 60mm scope with an 800mm focal length mounted on the back of the six inch refractor, and I clearly remember reading that Delta Cygni can be split in a 60mm scope. I start with the 7.5mm Celestron (107x) to see what I can see and I think I can just barely detect the secondary budding off of the primary. So, taking this a step at a time because every increase in magnification results in a dimmer image, I insert a 6mm Astro-Tech Plossl (133x) in the eyepiece and the secondary seems to be touching the primary. Next, I try the 5mm TMB Planetary (160x) and now I’m at least sure that I see a touching pair of stars. Back in the house again for more rarely used hardware, and this time I return with a 4mm Astro-Tech Plossl that has a lens on the top just slightly larger than a pin hole, but it jumps the magnification to 200x. Dropping it into the eyepiece, I slowly adjust the focus, and there — faint, dim, and a bit blurry at the edges, I see the two stars with just a very slight slice of darkness between them. I could go up to 3.2mm next, but that would yield 250x, and as dim as the image is at 200x, I suspect it would disappear entirely. So we’ll declare the battle over for now and claim victory. Best to quit when you’re winning. And anyway, this has been fun!
(The saga continues into the comments, so don’t stop here!)
** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **
It’s way past time I added a sketch of Delta Cygni to this post, so here it is!