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Delta [δ] (Wasat) and Kappa [κ] Geminorum, a Pair of Almost Identical Twins — and Let’s Not Leave out Lambda [λ]!

I was out a few nights ago lining up my scope on Polaris when I thought I heard a couple of voices coming from behind my left shoulder.  “Wasat?” I asked, as I turned around.

It was the Gemini twins, Jerry and George.  “Hey, Earth Guy!  You’ve been neglecting us for the past several months!”

Hmmm — I had to think for a second.  I remember having spied them back in the fall of last year clawing their way up from the eastern horizon in the early morning hours.  I had great plans for the two of them then, but aside from some time spent prying Propus apart, I just had not gotten back to them.

“Yeah, you’re right,” I said somewhat apologetically.  “If you can do something about this non-stop rotten rain we’ve had for the past five months, I would be glad to oblige.”

Jerry (he’s the east twin) looked at George (the western one) and rolled out a long, rumbling laugh.  “Yep, you’ve been gettin’ deluged down there, haven’t you EG!  We’ll talk to the Sky Gods and see if we can get them to let up a bit.  You know, trying to pass that old military surplus erfle off as an Ethos wasn’t too good an idea.  They’re still sore about that one!”

Jerry was referring to the eyepiece I had offered up a few weeks ago to the Sky Gods in hopes of better weather.  Yep, that one backfired.

“Yeah,” George chortled, “I got a kick out of that.  Not a bad eyepiece actually.  You want it back?”

“No, better let ’em keep it,” I said, “just see if you can exert some influence with those guys!”  I was afraid they might throw that heavy monster back down at me.  “Meanwhile, you have any suggestions?”

“Sure!” Jerry said, pointing to his east side.  “Take a look at Wasat and Kappa.  They’re almost identical twins, like George and me.”

“Wasat?”  I asked.  “What’s that?”

“It’s Delta!”  George said in his western drawl.

So that’s how I ended up spending three nights in a row with the Gemini twins.  And yes, photon deprivation affliction does strange, unpredictable things to the Star Splitting mind.

But I’m feeling much better now.  😉

The long-legged Gemini Twins are seen here dancing in the sky with outstretched arms. Jerry P(ollux) is on the left, George C(astor) on the right. Kappa (κ), Delta (δ), and Lambda (λ) are on the left of the chart, under Jerry’s influence. (Stellarium screen image with labels added, click on the chart for a larger view).

Wasat, AKA Delta (δ) Geminorum  (Σ 1066)  (H II 27)      HIP: 35550    SAO: 79294
RA: 07h 20.1m   Dec: +21° 59′
Magnitudes: 3.6, 8.2
Separation:  5.6″
Position Angle: 226°  (WDS 2009)
Distance:  59 Light Years
Stellar Classification: F0, K

Kappa (κ) Geminorum  (OΣ 179)        HIP: 37740    SAO: 79653
RA: 07h 44.4m   Dec: +24° 24′
Magnitudes: 3.7, 8.2
Separation:  7.9″
Position Angle: 243°  (WDS 2011)
Distance: 143.5 Light Years
Stellar Classification: G8, G4

As you can see, these two double stars are very similar in magnitudes and separation.  Despite that, Delta (δ) can be quite a bit more difficult to pry apart than Kappa (κ) — not really sure why that is, but it is.

The first night I took a try at these two was April 16th, with a 150mm f/10 refractor.  The seeing was absolutely horrible.  I’ll swear on a stack of late night Star Splitter snacks it was worse than the “I” shown on this chart.  Neither star would hold still for long enough to give me a cracker crumb of a chance of seeing the faint companion.

The next night, I was using an 80mm f/15 under slightly better seeing conditions — a “II” — and I thought I had a glimpse of Kappa’s (κ) faint secondary a couple of times, but again, it just wouldn’t hold still long enough to be sure.  What I needed was more magnification than I was using, but I had pretty well reached that night’s limit with a 12mm Brandon at 100x.

As bad as the seeing was, I also had to contend with the top of a star eating hemlock!  If you’ve never seen a hemlock, the tips of some of them tend to bend quite a bit, so instead of passing through a very thin, vertical branch-like top, I had to wait for the earth to turn and move Delta (δ) slowly through the top of a tree bent at about a forty-five degree angle.  And by the time it got through there, the seeing had deteriorated even more.

Ah  ……   but the next night started out with quite a bit more promise.  The previous two nights were plagued with a steady fifteen to twenty mile per hour breeze and clusters of white clouds that kept moving through in large tourist-like groups at unpredictable intervals.  This time it was calm, the only clouds visible were hugging the horizon, and the stars weren’t twinkling like spinning airport beacons.

I started with Delta (δ), AKA Wasat, because it’s the lowest and was subject to the horrible hemlock’s bent top if I waited too long.  I was intent on getting both of these stars, so I brought out the 127mm AR-5, on top of which is mounted an ancient Lafayette 60mm f/13.3 refractor equipped with a Carton lens.

Look closely to see Delta’s (δ) faint companion! East and west reversed to match the refractor view. Click for the image without this caption.

Starting with an 18mm Radian (66x), I saw a yellow primary, with just a bit of white in it, that was sitting absolutely still for a change.  A 14mm Radian (84x) didn’t bring out the secondary, nor did a 12mm Brandon (100x), so I gave a 10mm Tak  (118x) a chance.   Seeing at this point was a “III“, but at 118x, I was beginning to see quite a bit of hopping around in the eyepiece.  Then quite suddenly, the faint point of light I was looking for made a brief appearance, then disappeared, returned, disappeared, returned, etc., etc.  Not wanting to magnify my magnification too much more, I tried a 9mm Nagler (131x), and lost the secondary completely in the glow of the primary.  When in desperate need of a miracle, I usually pull out the magical and mysterious 7.5mm Celestron Plössl (157x) of Taiwan vintage, accompanied by incantations and toasts to the Sky Gods.  But  ….  since they seemed to be sulking over the erfle incident, I raised the 7.5mm Celestron in toast to Jerry and George and placed the chrome cylinder carefully in the diagonal.

This time I had it!  Finally, no question at all!.  I wanted in the worst way to stay with the magic of that eyepiece so I could enjoy the twitching interval of black space separating the two stars, but the image was just gyrating and jumping way too much for my eyes.  So back to the 10mm Tak I went, and then backwards again to the 12mm Brandon.  This time it was a bit easier to see the diminutive dance of faint photons rushing at me from that pinpoint of light, but it was so darned close to the primary that it was an on again-off again type of affair.  I saw the earth was about to spin it into the devouring hemlock, so unable to bear the agony of watching that tree devour Wasat once again, I crept up to Kappa (κ).

Kappa’s (κ) secondary is a bit easier to see in this sketch — east and west are reversed once again. Click on the sketch to lose the caption.

The color of Kappa’s (κ) primary is virtually identical to that of Delta (δ) — no surprise considering the twin-like characteristics of these two stars — although based on the stellar classifications, you would expect some difference.  I certainly couldn’t detect it.

And the secondary — well, to keep it short and to the point, it was hardly a struggle at all.  I was just able to detect it in the 14mm Radian (84x), and it was very clear in the 12mm Brandon (100x).  And this time, the 9mm Nagler (131x) pulled it out of the primary glow with ease.  At that magnification, the faint pinpoint secondary sits at a very comfortable distance from it’s brighter parent and is really quite a sight.  Actually, it’s very similar to the view of Polaris in a 60mm refractor at about 50x.

And that reminds me — just to illustrate how miserably miserable the seeing was two nights prior with the six inch refractor — I was able to extract the secondary in my 60mm f/13.3 with the 12mm Brandon (67x) with very little effort at all.  Maybe Jerry and George were having some luck with the Sky Gods after all.

But speaking of the Gemini twins, just as I was finishing a quick sketch of this area, I realized the seeing was slipping quickly back down the scale to “I” and worse.  I looked up from the eyepiece and found the light of the almost full moon reflected off some billowing white clouds that were staging themselves right at the tree line in the southwest and beginning a rapid advance in my direction.  First to disappear were Jerry and George’s feet, which I saw kicking like mad to get free.  The army of marauding clouds continued to march north, engulfed Wasat and the twin’s waists, advanced up to Kappa (κ), and then swallowed Castor and Pollux just as the twins yelled to me to watch out for rain.

So I quickly got everything off the deck in record time, and sure enough, I was barely in the house when a downpour of rain descended on the deck where I had so blissfully been absorbing faint Kappian photons just a few minutes earlier.

There was a brief roll of thunder — it might have been Jerry and George tussling with the Sky Gods — and I turned around, looked outside, and yelled up to them   ……….  “Wasat?”

Lambda (λ) Geminorum  (Σ 1061)             HIP: 35350    SAO: 96746
RA: 07h 18.1m   Dec: +16° 32′
Magnitudes: 3.6, 10.7
Separation:  9.7″
Position Angle: 34°  (WDS 2008)
Distance: 94 Light Years
Spectral Classification: A3, K8

Now, to get back to the real world for a short time — let’s not overdo it, though! — I came across Lambda (λ) the following night.  I was looking at Gemini in the Sky and Telescope Pocket Atlas and noticed Lambda (λ) wasn’t marked as a double, but I thought I had seen it in Sissy Haas’s Double Stars for Small Telescopes.  Sure enough, it was there, and looking again at the S&T Atlas, I saw that Wasat wasn’t shown as a double, either.  Strange — maybe it’s because the companions are so dim in comparison to the primary.

But let’s let Admiral William Smyth introduce this one:

A delicate double star on the left thigh of Pollux … “A”,  brilliant white:  “B”,  yellowish: the pair observed under the most favorable circumstances of weather and instruments, but the companion was seen best under an averted eye.”  (The Bedford Catalog: Willman-Bell, 1986, p. 171)

So I took a 90mm scope out that night and pointed it at Lambda (λ) and got it rather quickly with a 9mm Nagler (67x) and improved the view with a 7mm Nagler (86x).  It’s very similar in appearance to Delta (δ) and Kappa (κ), with the exception that the secondary is on the north side of the primary at thirty-three degrees, and I think it’s a bit easier despite the fact that the secondary is 2.5 magnitudes fainter.  I was able to see it without resorting to “an averted eye” — but you need dark skies.  Which was very evident as the moon came up and brightened the sky background, causing the secondary to begin a disappearing act.

Color wise, I saw the primary as pretty close to the same color as the Delta (δ) and Kappa (κ) primaries.  What puzzles me — and will continue to puzzle me until I can figure it out or see it for myself — is how anyone can detect any color in the secondaries of these three stars.   Once again, the admirable Admiral Smyth sees “yellowish” in this secondary, while I count myself fortunate to even be able to pry it out of the glare at all.  He also describes the Delta (δ) secondary as purple and Kappa’s (κ) as pale blue.  I’ve tried to detect a bit of color by de-focusing the stars slightly, but the secondaries are just too darn faint for that to work — more often than not, they just disappear from view.

Gotta be a logical answer somewhere to this puzzling puzzle. Hmmm, maybe I should consult with Jerry and George Gemini.  They seem to be well connected.

In the meantime, may your skies be clear, your lenses free of fog, your Star Splitter hat warm and dry — and the voices in your skies friendly!  😎


One Response

  1. Hello John,

    Very much enjoyed your writeup on these two gems in Gemini.

    I have been observing these on and off over the last few weeks. Like you, I find them uncannily similar, but to my eye I find Kappa Gem to be that little bit more difficult. Don’t know why. You would have thought the greater separation would make it easier!!

    if you pan northward into Perseus and zoom in on Epsilon Perseii you’ll get a similar kind of system. I observed this evening before the big bad moon got up. Primary (mag +2.9) secondary (+8.9) in about the 11 o’ clock position using my 5 inch f/9 achromat at 225x. The quoted separation is about 9″. A fine sight on a dark night!

    Finally, while in Perseus, I had to visit an old friend -Eta Perseii -a beautiful showpiece double for small ‘scopes. Though easily split in my 60mm even at low power, it looks positively resplendent with the greater light gathering power of my 4 and 5 inch refractors. Lots of fainter background stars resolved, which makes the view even more picturesque

    Best wishes,


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