Boötes seems to have more than its fair share of double stars — I can easily count about thirty of them on the main Boötes chart of the Cambridge Double Star Atlas, and there are at least ten more to be found around the fringes of a couple of other charts. I can’t help suspecting that when The Herdsman is hidden from sight in the daylight, or lurking on the opposite side of the globe, he’s busy dealing for double stars with his neighbors. At any rate, if you’re in search of multiple stellar scintillation, this can be a particularly productive happy hunting grounds.
On the other hand, if you like your stellar scintillation singular and on the particularly bright side, Arcturus really deserves a place at the top of your list. It gleams at a brilliant magnitude of 0.2, making it the fourth brightest star in the sky. Located a mere thirty-seven light years from where we orbit our own star, it’s surrounded by five very intriguing multiple stars that are under the influence of its soft glowing orange light. Three of them are doubles, one is a triple, and there’s even a quadruple hiding here.
And when you invoke some of the Greek terminology in this group of stars, such as Eta (η) and Pi (π), it’s possible to work up an appetite. Consider this conversation that might be taking place right at this very moment between two Arcturians:
“So, Blârgörkh, may I inquire as to what you ingested for an after dinner supplement this opulent orange evening?”
“I Eta Pi.” (I η π) …………………..
………………….. But we better move on. 🙄
We’ll start this tour in the west and work our way back to the east — and yes, there’s a good reason for picking this direction. The first night I went in search of these five objects, I started in the east and before I could get to Σ 1772 and S 656, they were swallowed by a cluster of ravenous coastal pines. So if you have similar obnoxious obstructions to wrestle with, this will help to avoid them.
And now …… on to Arcturus!
Eta (η) Boötis (Muphrid) (SHJ 169) HIP: 67927 SAO: 100766
RA: 13h 54.7m Dec: +18° 24′
Magnitudes: 2.7, 10.0
Position Angle: 86° (WDS 2011)
Distance: 37 Light Years
Stellar Classification: G0
We’ll start with Eta (η), also known as Muphrid, also known as SHJ 169, and located four degrees west of Arcturus. At a magnitude of 2.7, it’s the third brightest star in Boötes, so it would deserve a bit of recognition even if it wasn’t drawing our Star Splitting attention. Besides being located at about the same distance from us as Arcturus, it has begun to enter the “red giant” stage, so one of these days it will rival Arcturus in brightness. As far as the name goes — well no one really knows. It’s ancestry is Arabic, but beyond that, it’s a bit obscure. So we’ll leave it that way for now, although more information can be found on Jim Kaler’s Star Site. And, if you’re wondering about the SHJ designation, that comes from it’s place in James South and John Herschel‘s joint catalog of 1824 — on some star maps you’ll see the prefix “Sh” used instead, as in Sh 169.
This is an easy, wide double, although the tenth magnitude secondary can be a bit tricky if the moon is full. Fortunately, my first night with this one was about thirty minutes before a very bright waning moon rotated over the horizon. In my six inch f/8 Celestron refractor at 87x, the primary was a light shade of orange with a bit of white in it. The secondary was way too faint for seeing color, but otherwise it was no contest to find. Admiral Smyth saw “pale yellow” in the primary and “lilac” in the tenth magnitude secondary — but I can’t imagine how. Haas describes the primary as “Sun-yellow,” and the secondary as “a misty little dot.”
Faint and misty would be a better description of it. In my 60mm f/13.3 refractor it’s tenth magnitude dimness performed a dance of disappearance and reappearance. I had a glimpse of it in a 20mm TV Plössl (40x), lost it completely when I moved up to its 15mm sibling (53x), but got it back again with the 11mm (73x) TV Plössl. Then I had the brilliant idea that dropping back to a 24mm Brandon (33x) would defeat the glow and allow that tenth magnitude dim dot to pop into view …… but it didn’t quite work out that way. It was as baffling in the Brandon as it was in the 20mm Plössl. The seven magnitudes of difference in brightness between the two stars was really stretching the optical limits of the small refractor, so I patted it on the objective, said “good job,” and gave it a rest.
Σ 1772 (1 Boötis) HIP: 66727 SAO: 82942
RA: 13h 40.7m Dec: +19° 57′
Magnitudes AB: 5.8, 9.6 AC: 5.8, 11.9 AD: 5.8, 7.4
Separation AB: 4.5″ AC: 87.3″ AD: 208.4″
Position Angle AB: 133° AC: 25° AD: 1°
Data AB: WDS 2010 AC: WDS 2001 AD: WDS 2010
Distance: 303 Light Years
Spectral Classifications: A1 for all three components
Now if you take a peek in your finder (or look at the second chart above) you should see two stars, 7 Boötis (magnitude of 5.7) and HIP 67521 (magnitude of 6.8), just southwest of Eta (η). These two form a line that points northwest to our next star, Σ 1772. And a stunning little four-ple it is, too.
I had a mere glimpse of this one in the six inch Celestron about a week prior to the observation shown in the sketch, but it was inhaled by the pine trees and all I was left with was a tantalizing taste of what could have been. So I was more than eager to get back to it the first time the clouds parted, which took well over a week. Was it worth the wait? Is Jupiter a gas giant?
Yes, and Yes!
Now this one isn’t over-poweringly bright, but it kind of pulls you in by catching your eye with it’s two white wonders, “A” and “D”, which Admiral Smyth described as “sapphire blue” and “smalt blue.” And if you look closely, you can even pry 11.9 magnitude “C” out of the darkness in a 60mm refractor with some judicious use of averted vision — provided you have dark, reasonably transparent skies. I couldn’t see it in my 60mm f/16.7 at 50x, found it at 67x with averted vision, and lost it again at 91x — another dance of disappearance at the outer limits of the optical twilight zone.
But I recognized immediately that something was missing — 9.6 magnitude “B!”
Now, you would think that even with almost four magnitudes of difference, 4.6″ would be enough separation to spy this uncooperative companion with relative ease — or at least I did. And I really should know better by now — call it a case of over zealous zeal. Invoking the 2.51 rule — meaning each decrease in starlight of a full magnitude reduces the visible light by a factor of 2.51 — we find that “B” is about 39 times dimmer than “A” (that’s 2.51 to the fourth power). Now really, that still doesn’t seem like a lot, especially considering that for the star we just looked at, Eta (η), the tenth magnitude “B” component is 628 times dimmer than the primary. But we’re not helped at all by the fact that this 9.6 magnitude “B” is little more than a diminutive dot of light — and 4.6″ is nowhere near far enough away for that pinpoint of light to escape the glare engulfing it from “A.” So what all that adds up to is the fact that “B” is a bit of a battle.
In my six inch Celestron with an 18mm Radian (68x), I had a hint of it. Moving up a few notches to a 14mm Radian (87x) was enough to grab it from the glare, and as the sketch shows, it surrendered a solid split to a 2x Barlow loaded with a 24mm Brandon (101x). It still seemed to need more distance, though, so it was a real stroke of inspiration when I pulled the 15mm TV Plössl from it’s perch in the diagonal of the 60/1000 and dropped it into the Barlow. That allowed a leap skyward to 162x and a nice slice of black sky between the two stars — but as usual in my seeing challenged skies, it was hopping and twisting and diving and lurching and fidgeting and vibrating so much it was more than my eyes could keep track of for long.
So I backed off to the 14mm Radian again and just absorbed the view for another few minutes, until I glanced up and saw the approaching trees beckoning with their boughs …………….
S 656 HIP: 67543 SAO: 83022
RA: 13h 50.4m Dec: +21° 17′
Magnitudes: 6.9, 7.4
Position Angle: 208° (WDS 2011)
Distance: 338 Light Years
Spectral Classification: G0
……………. and I decided I better get moving before S 656 was gobbled up again.
Now this is another one of those situations where I found myself attracted to the configuration of the stars in the field of view more than the double star itself. After sliding two degrees to the northeast in the 8×50 finder, I leaned over to look in the 20mm TV Plössl (50x) sitting in the 60mm scope, and found my eyes drawn immediately to the two stars at the center of the field — and the one to the west, and the one to the east. There’s really little else in the field of view to compete for your attention.
If you look at the sketch, you can see that the “B” component of S 656 forms a line with 4.9 magnitude 6 Boötis to it’s west, and the “A” component forms a parallel line running in the opposite direction to 8.5 magnitude HIP 67591. Six Boötis is a beautiful star in it’s own right — a reddish-orange class K star located 368 light years from us. It’s partner on the opposite side of the field of view is notable for it’s distance, 1424 light years — which helps explain it’s lesser stellar magnitude.
But, this is about double stars, and James South’s catalog number S 656 is no slouch. Both stars are white, although there seems to be enough of a tinge of yellow in them to subdue the white light and lose the glowing headlight effect you get in bright class A and B stars. This is really a view that is ideal for a 60mm scope, but it doesn’t lose anything in a larger aperture, either. In the six inch Celestron, the subdued white glow of the “A” and “B” components is a rather remarkable contrast with the reddish-orange hue of the significantly brighter 6 Boötis.
So take your pick — sixty millimeters or six inches, or anything in between — and allow your eyes to relax in the expansive field of view as the photons of these four stars nourish your neurons.
Σ 1825 HIP: 69751 SAO: 83259
RA: 14h 16.5m Dec: +20° 07′
Magnitudes: 6.5, 8.4
Position Angle: 154° (WDS 2012)
Distance: 105 Light Years
Stellar Classification: F6
Now this one ……. this one is a star of a different color. But at a degree north of Arcturus, it’s easy to find.
I’ll turn it over to Haas first:
125mm, 83x: A fine star that’s nicely placed. It’s a bright amber-yellow star almost touching a little silvery globe. Easily spotted just outside the viewfield of Arcturus, which is about one degree to the south-southwest.”
Now my color perceptors didn’t quite see it that way — they reported orange and blue-white.
But regardless of color, I had to look real close to see two stars. It’s not that it’s a difficult double, but I had spent so much time soaking up the wide, comfortable field surrounding S 656 that it took a few moments to force my eyes back together in order to focus on the center of the field.
I came back to this one a few nights later, when my eyes hadn’t been widened by S 656 and it’s associates, and came away with a totally different impression. I was using my six inch f/10 refractor on a night with very stable seeing (IV) and transparency that was almost as good — and found the view in an 18mm Radian (84x) was simply beautiful. That little silvery globe that Haas saw was nestled right up against the primary at a bit more than hair split distance — and it struck me as a very delicate jewel of silver-blue light. This pair of stars pretty much dominates a fairly sparse field, although there is an interesting pattern of tenth and eleventh magnitude stars stretched across it to the north and west.
And if you look closely and carefully, that silvery little globe can be glimpsed in a 60mm f/16.7 scope at 50x — but you gotta peer pretty intently to catch it.
Pi (π) Boötis (Σ 1864) (H III 8) HIP: 71762 SAO: 101139
RA: 14h 40.7m Dec: +16° 25′
Magnitudes AB: 4.9, 5.8 AC: 4.9,10.6
Separation AB: 5.4″ AC: 127″
Position Angles AB: 111° (WDS 2010) AC: 163° (WDS 2009)
Distance: 317 Light Years
Stellar Classification: B9, A6
And now, if Blârgörkh hasn’t eaten it, we’ll head for the highlight of this tour.
Zeta (ζ) Boötis is located at the joint of the Hunter’s eastern knee, and Pi (π) is just a short two and half degrees north of it. Easy as pie ….. or a piece of cake ….. depending on what you’re having with tea after this tour.
Now this one IS a pair of headlights coming at you on a dark highway, especially if you’re using four or more inches of aperture. I don’t know where it’s been all my life, but if someone had introduced me to this gleaming white pair of stars with a whisper of gold in the primary a few decades ago, I would have become engaged on the spot. They really are an attention grabber. At the other extreme, the faint 10.6 magnitude “C” companion is easy to overlook — although at a respectable distance of just over two arc minutes, it’s visible in a 60mm scope with a bit of averted vision under dark skies.
But the A-B pair is a very attractive sight in a 60mm scope as well, which is what Haas was using when she described them as a “showcase pair . . . split by a hair at 35x.” My experience was the same, in both a 60mm f/15 at 46x and a 60mm f/16.7 at 50x. The beauty of the 60mm aperture is that it forces you to look closely to see the split. And if you do, what you’ll see are two very sharp, very well defined gleaming white stars that are so close together they couldn’t be any closer and still be separate. And that kind of split in a 60mm scope ranks right at the top of the many optical delights I’ve experienced.
Now if you had been splitting stars with the Herschels two hundred years ago, you might not have seen it that way. Jim Kaler writes that these two stars were about two seconds of arc further apart when William Herschel first observed them back in those pre-headlight days. But even then, they must have been a blinding sight in that huge reflector. (Click on the photo that comes up at the top of that page and you’ll get a much better view of the scope).
I’ll be returning to Pi (π) every time I have a clear sky this summer — in fact, I’ve already been back back to it a couple of times since the night I made the sketch. The brilliant white light escaping from these two white suns just begs to be captured in the circular confines of a telescope tube.
………. and since that ravenous Arcturian, Blârgörkh, left a piece of pie (π), I’ll go grab it while he’s practicing his Greek.
May your skies be clear and strewn with doubles of delight! 😎
(WDS data updated 7/16/2013)