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The Saga of Delta (δ) Cygni

Delta (δ) Cygni  (Σ 2579)  (H I 94)          HIP: 97165    SAO: 48796
RA: 19h 45.0m   Dec: 45° 08′
Magnitudes: 2.89, 6.27
Separation:   2.7″
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!

This isn't quite the 60mm battle described in the post above, but there's no denying Delta Cygni has an entrancing beauty that can only be experienced at much larger apertures.  (East & west are reversed here to match the view in the SCT, click on the sketch to enlarge it).

This view is a big improvement over what was seen in the 60mm battle described in the post above — there’s no denying Delta Cygni has an entrancing beauty that can only be experienced at much larger apertures.  In the 9.25 inch SCT, the secondary was absolutely fascinating to watch as it hovered clearly and distinctly within the radius of the primary’s glare.  Not shown here was a beautiful sharp diffraction ring surrounding the white primary.   (East & west are reversed here to match the view in the SCT, click on the sketch to enlarge it).

19 Responses

  1. Congratulations! And your comments on the Moon mesh with my own experience. For years I cursed it and let it cut my observing opportunities nearly in half. Now I love these moonlit nights for all the reasons you mention!

    However, don’t you think Delta would be just a tad easier – especially in the 60mm – in a dark sky? I’ve often used the Moon as an excuse when I don’t find the companion of Polaris in a 60mm. And I must admit, quite often I wimp out and don’t even try. In any event, here’s to your perseverance and success – looking through that 4mm must have taken you back to the days when all we had were Ramsdens – oh wait, improved “Achromatic” Ramsdens. 😉

  2. Yep – Delta is going to be a problem. Got out about 3:15 this morning to mostly clear sky after being shut out last night. The Moon and Jupiter were sure nice, though the Moon was still close enough to full – and high enough – to really wash out stuff. But all I was seriously interested in was Delta Cygni. Of course it didn’t help that the best scope I have for splitting it – the ES127 APO – was sitting 10 feet away in a locked shed – and I had misplaced the key! 😦

    It also wasn’t particularly helpful that seeing was poor – a “2” on a scale of 5. Still, it was good enough so I could split the Double Double with either a 2.5mm in the 80mm APO (195x) or a 7mm in the 15-inch (241X). Both splits were mushy with the 15-inch Obsession being particularly soft – but that’s normal for the 15. (Of course, I tried lower powers, but could not get a clean split.) While the 15 seldom does well on doubles – and Polaris was simple in it even under these seeing conditions – I thought it might help with Delta Cygni.

    No way! I kept seeing images I thought might have been the secondary, but every time I saw one it was at the wrong PA – not by a little bit, but by at least a quadrant – sometimes a half. So I’m sure I was just seeing – well – poor seeing.

    Here’s to clear – and steady – skies. Hope I get some soon.

  3. OK, it’s getting better – I had a window where I could get in a couple hours observing tonight, centered on midnight.

    Delta Cygni was high and while the moon was rising, it didn’t offer much interference. Seeing was still poor, but not as bad as last night, Using the the ES127 I picked up the secondary at the correct PA with a 5mm Nagler (190X), but I couldn’t hold it. In fact, seeing was still so poor that most of the time I couldn’t see the diffraction rings. But it would settle down and give me several seconds of clear seeing.

    I can’t get excited about it, though. The view was just too poor. I obviously need better conditions. I switched to the 15-inch and the secondary was quite bright in it – but again, the two stars clung to one another like a pair of soap bubbles, linked, and dancing in the wind. Then as the seeing steadied they would elongate some more and from time to time the secondary would break free, only to get sucked right back into the primary a moment later. I was using a 9mm Nagler – 187X.

    I went back to the 5-inch and couldn’t find the secondary at all, so I decided this really wasn’t a double star night. I switched to enjoying some familiar objects with the 15-inch, it’s mirror has been freshly recoated. It was exciting to see all the detail in M51, M13, and M11 – even with the Moon over my shoulder. This is a case of absence making the heart grow fonder. I haven’t used the 15-inch for about six month, but I think I had become almost jaded with these views – I didn’t appreciate them – and, of course, the mirror had gotten in pretty bad shape – it really did need the recoating. I saw enough to really enjoy myself and I know the 15-inch is really going to help visitors, looking at these objects for the first time. Of course, it still isn’t a double star scopes. It can find some special duty inthat respect, but it will never have the crispness of the refractors.

    • Ah, the refractor vs. reflector dilemma! For deep sky, there is no substitute for aperture. But for tight double stars, the unobstructed aperture of a refractor seems to me to be a necessity. I would love to get a look at M51 in a fifteen inch Obsession, I must admit!

      Delta Cygni is one of those doubles that requires very good seeing, though, regardless of what scope you use. I had the Zeiss 63mm out a couple of nights ago, hoping to get a shot at Delta again, but I was being out-maneuvered by the clouds. Every time it was clear in that direction, the clouds reversed direction and covered it up again as soon as they saw me move the scope in that direction.

      But, regardless, I’ll be back again!

  4. At last – getting some more serious steadiness out of the sky – from time to time on the good side of average – occasionally real good. The result was an easy, clean split with the 127mm and an absolutely charming split with the SV80 Lomo triplet. I’m wondering, though, if I would have seen it at all if it hadn’t been for your report, John! The secondary appears much fainter/smaller than I would expect for a magnitude 6.3 star, presumably because of proximity to the primary. If I assigned a color to it, it would be gray next to a white primary – but that color may be more a reflection of contrast in brightness rather than real color. .

    I actually preferred the view in the 80mm.There was something nearly hypnotic about that tiny pinpoint of light next to the primary. But I still don’t think I’ve seen Delta at its best. As often happens with good seeing, transparency was terrible. At times I had Mag 2 skies and I rarely got to see a 4th magnitude star with my naked eye as high clouds filtered through.

    It took a 2.5 mm Nagler – 192X – to give me the split with the 80mm and while it would split with a 5mm – 190X – in the 5-inch, it was better with the 3.5 Nagler – 272X.

    Oh – a little later I tried the 15-inch – no luck. At that time the seeing had deteriorated.

  5. July 3rd/4th, 2010, 2330 to 0030

    Star bright, starlight,
    are you going to give me a clean split tonight?
    Or will it be a struggle and a fight
    to get a split that’s even slight?

    OK, bad poetry, but this star doesn’t give anything up easily.

    I just happen to have a Zeiss Telementor, 63mm in aperture, 840mm of focal length (which makes it f13.3), that was begging for a chance to split Delta Cygni since it’s rival, a 60mm/800mm with a Carton lens, had beaten it to the draw the week before, as described above. The two of us were all set up to give it a try the previous night, but just as we got situated and I had dropped a 6mm eyepiece into the focuser, the clouds threw a blanket over Cygnus and left it there.

    So, we’re back again tonight. The seeing tonight is about a notch less than it was last week at this time, but the transparency is slightly better. So, all things considered, apart from the occasional explosion of artillery-sized fireworks that cause me to jump about twenty feet off the deck, it should be a good night.

    I start with an 18mm Radian (47x) just for locating purposes, and once I’ve got Delta Cyg in the view, I switch to a 10mm Radian (84x), hoping for quick success. And …….. well, it was only a hope. From there I move up to my trusty 7.5mm Celstron Plossl (112x) – – still not the least bump on the primary. I see now that I’m beginning to get some noticeable atmospheric vibration in the eyepiece. Next move is to a 6mm Ortho (140x) that I picked up used last week – nice view, and a pleasing diffraction ring, but still no sign of that beady little secondary.

    At this point I’m beginning to wonder if there’s any chance at all tonight, but a switch to a 4mm Plossl (210x) hints that the secondary is hiding in the diffraction ring. Now it’s time to get serious and blow the dust off of two eyepieces I haven’t used for well over a year – a 3.2mm TMB Planetary and and it’s ultra high-powered 2.5mm sidekick. The 3.2mm yields 263x and a reasonably focused image, but still no secondary after looking hard for about five minutes.

    With some hesitation and a lot of doubt, I swap that one out and replace it with the 2.5mm and a huge leap to 336x. Expecting an image reasonably equivalent to a black hole, I find I can get a soft focus on a dim star and a ragged diffraction ring, which is jumping around quite a bit. Still nothing I can call a likely candidate for the secondary, though.

    Well, what’s next? I can’t go any higher in magnification, and there wouldn’t be any point if I could – if 336x doesn’t do it, nothing else will either. I decide to switch back to the 3.2mm in hopes that the slightly clearer image will give me a better chance. So, out with the 2.5, in with the 3.2, and a long hard stare of several minutes. Finally, between the edge of the primary and the diffraction ring, I can just BARELY detect a little dot that is just BARELY separated from the much larger primary. As I watch, it merges with the diffraction ring, and then pops back into view several times. I put the 2.5mm back in again, and this time I can see it more clearly – not sharp and distinct by any means, but much easier to see in the space between the diffraction ring and the primary.

    After giving it some thought, I reach the conclusion that this split ought to be possible in the Zeiss at less magnification, so I decide to run back through the eyepiece selection in reverse. First the 3.2mm goes back in, then the 4mm, then the 6m, and finally the 7.5mm. Now that I know EXACTLY where to look – and having seen it last week, I thought I already knew that – I’m able to pick out that beady little dot – either in the space between the diffraction ring and the primary, or right up against the edge of the diffraction ring. The problem is that it keeps merging into that ring, and seems to disappear unless you know exactly where on the ring to find it. And the difference in seeing between last week and tonight is just enough to turn this into a real struggle.

    Considering that the seeing is slowly deteriorating as the next weather front approaches, my timing tonight is much better than it had been the previous night. The Zeiss is content now to have matched the Carton lens, so it’s time to leave Delta Cyg alone for a while and move on to other challenging objects.

    But don’t neglect this one if you haven’t tried it – not only is it a good test of optics, it’s a great way to improve observational skill.

  6. Up at 3:15am and surprised to find clear and steady skies. I rushed out to the Observing Deck to take up John’s email challenge – that I test the new – to me – test the AR-5 achromatic on Delta Cygni.

    And yes, it passed the test quite easily! Not bad for a scope I paid $200 for used – not bad at all. In fact, this is my best view to date of this challenging little double, but I don’t think that’s because of the scope. The seeing is well above average and the Moon is quite far away – in the east while Delta is in the northwest – and at last quarter. The split came with a 5mm Nagler (236X) – but I switched to the 6-3 Nagler zoom -196X – and the split was fine – plenty of black sky.

    I also cranked the power up on this to close to 400 and it became easier – though I think the best split was in the 225-300 range. I also split it with the 100mm Orion F6, though this was more difficult and required the 2.5 Nagler (240X) for me to see it clearly.

  7. OK, Delta is becoming a test fo r new scopes now – not to mention conditions. So I tried the new (tome) Orion 110 ED. This is an F7 refractor that fits nicely in the little observatory, but I wasn’t sure what it could do. It was twilight and had just gotten a clean split of the Double Double – very nice split, really. So Delta should be easy.

    Wrong. This is a pesky double! I don’t have a finder on the new scope and because the split was so difficult I kept checking to make sure I really was looking at Delta. I gave up after trying the 6-3 zoom on it and getting no where. I decided the seeing wasn’t as good as it seemed. Or maybe the 110 wasn’t.

    Nearly four hours later I was ready to close up shop, but Delta was practically at the zenith and everything I tried had been splitting beautifully, so I couldn’t leave it alone. (There was an 11-day moon low in he southwest generally washing things out.)

    Now I pointed at Delta, was certain I had the right star with a little check mark asterism of three stars next to it, and bingo! Terrific split using a 2.5mm Nagler – 308X. Oh it would split with less. But the conditions allowed the extra power and that extra power turned a routine success into a very attractive double – first time I’ve reallyf elt that way about Delta. But it has been a saga!

  8. Hi Greg,

    Delta Cygni is one of my staples during the summer. I have enjoyed some lovely views in my 4″ refractors but recently I decided to test my 80mm F/11 refracor on this notoriously tricky pair. For some reason, this telescope works especially well with my 5mm orthoscopic yielding 180x.
    The weather this June has been rubbish on the whole, but on two calm, clear nights, I decided to turn this little telescope on the pair. The first time I tried was on the night of June 3 about 12.30am. and last night, June 16 – at around local midnight and was delighted to cleanly resolve the pair. The little spark of a companion was seen in the ten o’clock position using my set up (1.25″ dielectric diagonal).
    I wonder if anyone here has achieved a clean split of this system with an 80mm scope.



  9. Hi Neil, not yet is my optomistic response. I only have a Celestron ED 80 which has given me some memorable views of doubles taken from Greg and John`s excellent posts- particularly when the seeing is IV or better on their scale. Am moving tomorrow to the top NE corner of Portugal from the Algarve for 3 months. I hope the skies will be as steady as they are clear up there. On a technical point i note your successful split was with a dialectric mirror diagonal. I switch between a Burgess CED 1 mirror diagonal and a Baader (T2) Prism as my scope`s f-ratio ( 7.5 ) might be on the cusp as to which better fits the scope`s optics. I have never done a direct comparison in the same evening. I decide during the day which one to fit and that could stay for several nights. I like the bright images in both. However real success with faint secondaries – aka “C” in sigma Ori and all 6 stars in “Stargate” pushes me to take only the Baader prism up north. Am interested in any comment you might make on the “accepted ” proposition that a long focus refractor benefits more from a prism ? Obviously faced with a tough split you would give yourself the best set-up. Anyway i have another summer project with D Cygni and a lovely area of sky to explore around it. Hope you get better skies this summer. regards, rich.

  10. Hi Rich,

    Portugal? Wow! I envy you. Just think of the tally of clear nights you’ll get there compared with the UK.. In any event, I wish you a very smooth move.
    I’ve been having a lot of fun with my A-P 80mm f/11 guidescope which I have discovered to be a fantastic double star bagger for its modest aperture. It cost me hardly anything but it has already paid for itself many times over.
    At your new, lower latitude, you’ll get a much better view of Antares.
    It’s a hopeless cause this far north (56 degrre N).

    Best wishes,


  11. Hi Neil thanks for your good wishes. The skies here are usually very clear. However the seeing last night was only II on the roman scale that Greg & John use. Nevermind, i got a stunning view of the “glowing” Ring Nebula as compensation. Hope your skies cheer up!
    regards, rich.

  12. 12:30 AM, July 10th, 2011

    What does Delta (δ) Cygni look like at 750x? Strange you should ask — but I think I know someone who just might be able to describe it!

    It had been a while since I looked at Delta (δ) Cygni, so when I spied it climbing the eastern sky early this morning, I swung my six inch f/10 refractor over to it and centered its gleaming white light in the little 6×30 RACI finder. Yeah, I know — what in the world is a little finder like that doing on such a big scope? Hey, it works! And pretty darn good, too.

    But to get back to Delta (δ), I see from the post above that at about this time last year I had a tough time of it in a six inch refractor. Not now, though.

    I swapped the 18mm Radian (83x) for a 10mm Radian (150x), rotated the focus knob a revolution or two, and watch the glowing white primary slowly come into focus. And right beside it was a beaming secondarial dot of light that was slightly less white, separated from its larger brother by a thin slice of interstellar darkness

    On the first try, no less!

    I had the 7.5mm Celestron Super Plössl handy, which would boost the magnification up to 200x, so I gave it a try. The result was a slightly larger image with slightly more space between the stars, and the beginning of a diffraction ring around the primary. But — the main thing was the image was reasonably steady.

    I was about to leap to my feet to celebrate, but I decided instead to leap up to a 4mm Astro Tech Plössl — a strenuous leap it was, too, because it magnified Delta’s (δ) photons to a giddy 375x.

    Now this was nice! These two stars are 2.5″ apart, although you would never know it looking at the image in the eyepiece. Both were dancing and shimmering quite a bit, but they were distinct, they would hold still long enough to capture a few visual snapshots of them, and if I hadn’t known they were magnified 375 times, I would have thought there was enough space between them to build a four-lane highway. OK, slight exaggeration — but you should have the picture now.

    Which is important in order to understand why the next idea came barreling into my brain. There was a 2x Barlow lens in my eyepiece box that I had been using earlier on something or other — can’t remember now what it was — but some sneaky gremlin of the night beamed an image of that thing at me, and suddenly I saw the possibility.

    “Naw, never going to work. 750x? Are you kidding?”

    “No. Try it.”

    I don’t know where that voice came from, but I tried it.

    And it worked. It really worked! It ACTUALLY worked!!!

    So here’s what it looked like: BIG!

    HUGE even!

    Now you would expect the image to be fuzzy, and it certainly was that. And you would expect it to be hopping around like a gnat in a hot iron skillet, and it was. But I could focus it well enough to clearly distinguish both white globes — although the diffraction rings were shimmering so much that at times they almost obscured them.

    And there was LOTS and LOTS of space between the two stars. It would be exaggerating to say they took up most of the field, but when you take into consideration all the spinning, gyrating, and bouncing back and forth they were doing, there certainly wasn’t much unoccupied space in that field of view.

    And that’s what Delta (δ) Cygni looks like at 750x.

    If your skies are steady, give it a try.

    Listen to those voices in the night — some of them actually have a lot of observing experience! 😎

  13. The question before us tonight is: Can we separate Delta Cygni into one solid trembling white star and one very small dot of elusive quivering light nestled up next to it? “Trembling” and “quivering” are required adjectives when the seeing is about a II — at least during the better moments.

    Which will prove to be darn few.

    On the left we have an Orion 90mm f10 refractor. On the right, and outweighing it by a few pounds, we have an 80mm Mizar refractor with an f15 Carton lens. One of them should succeed.

    We hope.

    We begin with a 20mm Astro Tech Plössl (46x) in the Orion as a sort of wide field eyepiece. Stars are very sharp pinpoints of light at that magnification and the sky background is jet black. And the field of view is as stable as a 50mm finder on a twelve inch pier set in concrete . . . . . if only it would stay that way when the magnification increases.

    Fat chance.

    On the 80mm side of the mount, we start with an 11mm TV Plössl (109x). No dice, but lots of shaking goin’ on. No surprise there.

    But we’re not here to stop.

    So the next tool of choice is the 7.5mm Celestron Super Plössl (160x). The primary is flitting around like a moth around a lamp, but there seems to be a speck of something at the correct PA hanging on for dear life.

    OK — out comes the 7.5mm and in goes an Astro-Tech 6mm Plössl (200x). Bending down to the eyepiece, I see so much hopping and leaping and bouncing around in the field of view it looks like a fight has broken out in a pinball machine. I half expect to hear bells going off and see lights flashing.

    Wait a second — I do see lights flashing. Right at the edge of the primary. And just for micro-seconds of a moment — just so briefly that if I blinked I would never see it — is a little speck of light barely separated from its much brighter and larger caroming companion.

    Houston — come in — we’ve just made a rough landing!

    Now just to make sure — it’s always good to be sure in cases like this, when quick glimpses are all we can grab — let’s try a 4mm Astro-Tech Plössl. That translates to 300x and a field of view of eighteen hundredths of a degree — about enough to catch these two stars once an hour as they bounce back and forth across the field.

    OK, it’s not quite that bad. But did you ever try to track two stars, both of which are intent on setting a broad jump record, with a non-driven alt-az mount in a space as restricted as that? The cranial circuits beneath my Star Splitter cap suddenly spring to life — and prompt me to place Delta just out of sight at the bottom of the field so it can drift into sight — and out of sight.

    It takes about four seconds.

    So I have to look quick. And yes, it’s really there. That little dot of elusive leaping light.

    As I breathe an accomplished sigh of relief, I look up — and see clouds. I turn around, and see more clouds. In fact, the only place there aren’t clouds is where I have the two scopes pointed.

    Really strange. Normally that’s the first place they go.

    So, not a moment to waste. I go for broke and drop the 4mm AT Plössl (228x) into the diagonal of the 90mm scope, get a firm hold on the edge of my chair, and prepare to have my eyes assaulted by unfocused and unsteady out of phase photons.

    Which is pretty much what happens.

    But that little speck of dot-like light is there when the photonic phases coincide! Not for long, since the field of view isn’t much better at twenty-two hundredths of a degree.

    But we have two-x success.

    We can call this round a rousing tie and retire for the night with a grin on our face — after a few scowls at the clouds.

    But to switch to a more serious tone now, even though I was able to pick out that miniscule little companion in the glare of the primary, I would not call it a satisfying view in either of the scopes. If the seeing had been better, I think it could have been rather memorable, judging by what I could see of the two stars when they held still long enough for me to capture a good visual snapshot of them. I really would love to look into an eighty or ninety millimeter scope and see that petite point of light sitting calmly next to its much larger companion as opposed to spinning like a whirling dervish.

    So far, the memorable view of Delta Cygni remains with the six inch f10 at 375x that is described in the comment above this one.

    But there are a lot more nights where this one came from. 🙂

  14. Congrats John,

    Fantastic delivery!

    Catching the demon companion of Delta Cygni ain’t easy with an 80mm scope of any specification but like you’ve handidly shown, it’s certainly possible with the right approach.

    I have split this system before on one occasion with a 76mm ED scope at ~200x, but recently I have been using a very nice 80mm f/11 achromat that works superbly with a 5mm orthoscopic eyepiece delivering 180x. It was with that 5mm eyepiece that I resolved this pair.

    It is so much easier with a 4″ glass though and a 6″ makes light work of it.



  15. Here it is, ten days to the Summer Solstice, and Spring hasn’t even made the first attempt to spring. Not even a little leap. Two nights ago it was a bone chilling forty-two degrees. Great for January, unbelievable for June.

    And along with all that there has been a virtual absence of clear skies. Now don’t confuse that “virtual” with the “virtual” in “virtual particles” — which at least pop in and out of existence — because once the clear skies popped out of existence, they didn’t pop back — they were gone for good. Or at least it sure seemed that way.

    Anyway, it was clear at 2AM this morning, and when I saw Delta Cygni beckoning high in the sky above me, I just could not refuse it.

    Up into the air I swung the immaculate white tube of my six inch f/10 refractor, gleaming with the reflected weak light of a last quarter moon an hour above the horizon, and re-introduced it to Delta. It didn’t take long for it to remember Delta’s gleaming white light as it called up last July’s 750x experience (in the third comment above this one).

    I had forgotten the PA of the secondary, but I thought I had a glimpse of a pinpoint of light in a 14mm Radian at 109x, so I went to a 10mm Radian and 152x, and sure enough, that was it. So then I unfolded myself from my low crouched seat, stretched my cramped muscles as I ambled into the house to un-box a a 6mm Radian, strolled confidently back to my low-down seat, applied all 253 x’s to Delta’s dueling white lights —- and I didn’t move. Not for a long while.

    There were two or three diffraction rings pulsating around the primary, and every now and then the secondary would merge with the outermost ring, and then suddenly pop free again. In and out, back and forth, shimmer and spin and circulate and halt and then do it all again — darn, what a sight. What A Sight!

    When it was outside the rings, the secondary was a dinky little dot of pristine white light. Just fantastic.

    Now picture this: One large and round and white ball of light; two and three pulsating diffraction rings that were doing a convincing imitation of strobe lights — and that dinky white dot of secondarial light sitting there just outside the rings, and then in the outermost one, and then out, and then in, and back out —- and in and out, and in and out ……………………………………..

    I literally wore my eyes out on that image. I stared so hard and for so long they both began to water. Which blurred the image. So I would look away for a few seconds, go back and look again until the image began to blur, look away, look back …………. I’m sure you get the picture.

    What an amazing way to cap the end of Spring!

    • Hi John, I too last night had my first look at Delta Cygni I was
      using 100mm Tal refractor, the seeing was pretty good but even
      at 200x I could not tease out the secondary so I switched to the 80mm
      Zeiss. My original thoughts were right the seeing was good there was Delta surronded by 3 diffraction rings almost steady but not
      quite I increased the power to 200x the view was still sharp and there
      were moments when I caught the secondary hiding behind the rings.
      I could not say I split it as the moments when I caught the secondary
      were very brief maybe even my imagation but the view of that little
      dot was magical.


  16. Delta Cygni is my favorite double, and I never miss an opportunity to look at it **when the seeing is good**. For me it is a test of the seeing, not the telescope. I have seen it in an 80 mm and failed to see it in a good C11. When the seeing is fine I think it is prettiest in my C102F at about 150X, … clear but delicate.

    I think the reason it is so difficult is that the secondary tends to fall on, or very close to, the first diffraction ring of small telescopes. I think it’s also more difficult to see it in reflectors because the diffractions rings are brighter than in equal sized refractors.

    Astronomers with a good quality 80 mm refractor should be able to see this beautiful double, but only when the seeing is very steady.


    • Hi Phillip,

      You’re exactly right about that secondary falling on the diffraction ring in smaller scopes. I had a four inch refractor out a few nights ago, and could barely pick out the secondary because it was clinging to the outer edge of the diffraction ring. I’ve noticed the same thing in 90mm, 80mm, and 60mm scopes, which adds considerably to the difficulty of seeing it.

      It’s free of the diffraction ring in both five and six inch refractors, and is a thing of absolute beauty when you use can use enough magnification to get a clean split. There’s nothing like the sight of that round white dot of light floating just out of reach of the primary!

      Welcome to the site!


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