A strange thing happened while I was on the way to Cygnus . . . . I found myself in Pegasus. Now actually, that’s not as unlikely as it seems. Even though we (or at least I) think of Cygnus as a summer constellation and Pegasus as an autumn constellation, they actually border on one another. If that surprises you, look at a star atlas and you’ll find Mu (μ) Cgyni resting barely inside Cygnus’ northeastern border.
All it would take is a slight celestial nudge to push it into Pegasus. In fact, by my measurements, Mu (μ) is a mere seventeen degrees from Beta (β) Pegasi and just a few furlongs further from Alpha (α) Pegasi at twenty-two degrees.
Now when I look at chart number six in The Cambridge Double Star Atlas, I don’t see a lot double stars in Pegasus, especially inside the area known as the Great Square. In fact, within the area bounded by that slightly irregular rectangle there are only eight double stars identified by name. And if you inspect all 240 square degrees of that area a bit closer, you’ll struggle to come up with even a half dozen more no-named pairs. A veritable double-star desert, so to speak.
But as Chris Thuemen, who has photographically corralled a veritable herd of double stars in Pegasus, mentioned to me, you just have to look a bit deeper. They’re there. In fact, it was his photo of the Σ 3060-3061 pair that roped me into throwing a six inch refractor into the saddle of a large mount and taking a gander. Chris, by the way, is the brains behind this site, which is devoted to photographing all the double stars within reach of the lens of his refractor.
But enough of this horse talk. Let’s spur ourselves into action – we’ve got a heap of hedges to leap.
From 2.45 magnitude Markab (this will open the chart above in a second window to make it easier to follow along), you can move three-fourths of a degree south to 7.10 magnitude HIP 114028, then go a degree due east to 6.50 magnitude HIP 114378. From there, it’s a long northeast leap of four degrees to HIP 115288, which is parked just northeast of a distinctive arc of seventh and eighth magnitude stars easily seen in an 8×50 finder under reasonably dark skies.
Or, you can start at Markab and move a bit more than a degree north to 6.40 magnitude HIP 113994, then head northeast almost two degrees to 5.65 magnitude HIP 114449, and next go east with a slight tilt to the south a total of about two and a half degrees to HIP 115288.
From HIP 115288 if you look a degree and half to the southeast, you’ll see a parallelogram consisting of 7.45 magnitude HIP 116021, 7.95 magnitude HIP 116091, 7.10 magnitude HIP 115910, and at the northwest corner our faint targets, Σ 3012 and Σ 3013, looking for all the world like a single star.
Σ 3012/Σ 3013 HIP: 115800 SAO: 108618
RA: 23h 27.6m Dec: 16° 38’
Identifier Magnitudes Separation Position Angle WDS
STF 3012 AB: 9.47, 9.82 2.80” 190° 2012
STF 3012 AC: 9.47, 8.51 52.20” 66° 2012
DOB 18 AD: 9.47, 10.20 49.50” 64° 2012
STF 3013 BC: 9.82, 8.51 53.80” 64° 2012
DOB 18 BD: 9.82, 10.20 51.40” 62° 2012
STF 3013: CD: 8.51, 10.20 3.10” 277° 2012
Distance: 247 Light Years
Spectral Classification: “A” and “C” are G0
And as you’ll quickly realize, you need to sit up straight in the saddle and get a firm grasp on the reigns in order to pry these two tight pairs apart:
Now I gotta be honest – the first time I looked at this pair I couldn’t see any duplicity. I think that was with a four inch refractor on a night when the seeing was shakier than the view from the top of a horse streaking for the finish line at the Grand Prix de Paris. The 2.80” and 3.10” of separation is well within reach of a four inch refractor, but the dearth of starlight is really a heck of a hurdle to overcome, and unsteady seeing certainly doesn’t help matters.
I did better with a five inch refractor, and of course a six inch improved the view – although not by much. But once you manage that first rewarding view of the delectable slices of black sky intervening between the AB and CD pairs, you might just find yourself returning again and again. I can’t recall ever having seen a pair of stars in this configuration – the way they lean into each other is unique.
However, if the tight distances and faint photons cause your telescope to rear up on the hind legs of its mount in disgust, don’t despair. If you take a look at this list of observations in Lewis’s compilation of Struve’s stars, you can see they’re slowly moving farther apart. So give it a few hundred years and the view will improve.
While I was roaming around this area, I came across a rather interesting Struvian triple, Σ 3021, which had concealed itself as HIP 116691 a short degree to the southeast. I made a mental note to return, and although it took almost a month, I finally found my way back.
Σ 3021 HIP: 116691 SAO: 108659
RA: 23h 31.4m Dec: +16° 13’
Magnitudes AB: 8.06, 9.26 AC: 8.06, 10.79
Separations AB: 8.90” AC: 118.50”
Position Angles AB: 308° (WDS 2012) AC: 23° (WDS 2012)
Distance: 727 Light Years
Spectral Classification: “A” is F8
Once again, the seeing was poor when I got my first look at this triple delight. I don’t know what was in the air, but in addition to the quivering image, I had the impression I was looking through a layer of mud. It’s possible there are some dimmer stars to be seen in this field on a more transparent night, although considering the conditions, this turned out to be an interesting threesome of stars. But what I wouldn’t give at times for a stall full of stable skies.
Now don’t yank your boots out of the stirrups just yet! We’re going to trot over to the opposite side of the Great Square now for our second pair:
From 2.80 magnitude Algenib (here’s that second window again), move north about one and half degrees to 6.50 magnitude HIP 1057 and then bend northwest and move about the same distance to 5.55 magnitude 87 Pegasi. In you finder you’ll see a skewed rectangle consisting of 87 Peg, 7.45 magnitude HIP 493, 6.55 magnitude HIP 258, and 7.05 magnitude HIP 759. Move a distance of about three quarters of a degree across its north edge to HIP 493 and center it in your finder. As you start to move your scope south, the first of our two stars that comes into view is Σ 3060 which is just nine arcminutes south of HIP 493.
Σ 3060 HIP: 495 SAO: 91707
RA: 00h 05.9m Dec: + 18° 05’
Identifier Magnitudes Separation Position Angle WDS
STF 3060 AB: 9.32, 9.65 3.40” 135° 2011
STF 3060 AC: 9.32, 12.15 66.50” 272° 2011
LEP 1 AD: 9.32, 7.47 573.20” 359° 2000
LEP 1 AE: 9.32, 16.58 999.90” 267° 2000
Distance: 127 Light Years
Spectral Classification: “A” and “B” are K0; “D” is F8
Notes: AC is an optical pair; AD is also HJL 1001 and SHY 112; AD (“D” is HIP 493) is also probably a physically related pair, with both stars moving parallel to each other at the same apparent rate.
Here’s the first view:
And as you continue to move your scope south, you’ll see Σ 3061 come into view just 14 arcminutes away.
Σ 3061 HIP: 482 SAO: 91703
RA: 00h 05.7m Dec: 17° 50’
Magnitudes: 8.40, 8.51
Position Angle: 149° (WDS 2009)
Distance: 548 Light Years
Spectral Classification: F2, F2
This pair of doubles is a bit easier to see than the first pair, thanks to wider separations. I haven’t tried them in a four inch refractor, but neither pair should be out of reach under average seeing conditions considering how easily they separated with the five inch used for the two sketches.
Where this pair differs considerably from the first pair is in their rate of proper motion. Σ 3060 in particular is sprinting through the galaxy as if it was a thoroughbred streaking for some imaginary celestial finish line. In the notes I attached to the data above for Σ 3060 you’ll see a comment about the AD pair moving parallel to each other, which is quickly apparent in the Simbad plot below:
And when we flip the Simbad switch and narrow the field of view from fifteen minutes of arc to five, we see the AB pair is moving parallel to each other as well:
The proper motions illustrated so well in the two charts for “A”, “B,” and “D” are:
STF 3060 A: -146 RA, -146 Dec
STF 3060 B: -154 RA, -155 Dec
STF 3060 D: -149 RA, -151 Dec
Those figures represent thousandths of arcseconds per year (as in .146”), with the negative sign indicating westward motion in right ascension and southerly motion in declination.
That first chart also showed noticeable movement for the Σ 3061 pair, which is revealed more clearly when we zoom in three times closer:
The proper motion for these two star is:
STF 3061 A: +060 RA, -018 Dec
STF 3061 B: +055 RA, -014 Dec
Now if you go back to the first of the three Simbad charts, you can see the Σ 3060 pair is moving southwest as the Σ 3061 pair moves almost due east. So given enough time, they’ll eventually put enough distance between them that we’ll need a wide-angle eyepiece to keep them within the same field of view. Maybe by then the optical magicians at Tele Vue will unlock the secret to providing eyepieces with apparent fields of view of two hundred degrees.
While you’re thinking about that possibility, I’m going to reign in my eastward motion and gallop off to the west. I need to catch Cygnus before it flies out of sight for the season.
Clear Skies! 😎