Tonight we’re beaming up to a remote sector of northwestern Boötes to explore a dim, neglected section of sky that cuts a narrow swath through the middle of the Herdsman’s club. There isn’t any blinding light from dualing doubles to be seen here — although the last one comes close — but there are certainly some subtle visual delights to be savored in this no-man’s land of sparse light.
But the first question you probably have has to do with what in the world drew me to these stars.
Star atlases are like road maps, promising unique adventures in unknown territory. When I see the names of little known towns in the middle of nowhere on a map, I can’t help but wonder what the real thing looks like up close. Or when I scan a U.S. Forest Service map of a wilderness area and see faint trails wandering through a maze of topographic contours, my imagination runs rampant with thoughts of the sights to be seen there.
And it’s no different when I look at a star atlas and see those horizontal lines drawn through the dots that represent stars — my curiosity soars to the surface with thoughts of what those dim points of light must look like. That’s especially the case if I see a star that’s marked as a double, but without an identifying name next to it — which is the way the last three stars we’re going to look at here are shown in the Sky and Telescope Pocket Atlas. Or especially if I see a star not labeled as a double when I’ve seen it referred to as one in a printed source — which describes the first one.
And that’s where we’re going now ……………………..
13 Boötis (H VI 112) HIP: 69068 SAO: 44905
RA: 14h 08m Dec: +49° 27′
Magnitudes: 5.5, 11.0
Position Angle: 271° (WDS 2005)
Distance: 557 Light Years
Spectral Classification: M1.5
If you draw a line from Lambda (λ) Boötis to Kappa (κ) Boötis, you’ll find 13 Boötis lying at the midway point and about an arc minute west of it. I can pick out it’s fifth magnitude glow with both of my naked eyes working in harmony, thanks to dark skies, and it’s distinctive reddish glow is easily spotted in binoculars or a finder.
This one caught my eye because I saw it referred to in the Cambridge Double Star Atlas with William Herschel‘s distinctive designation. In his catalog of 1782 to 1784, the Roman Numeral “VI” (6) identifies it as having a separation of between one and two arc minutes. If William Herschel took the time to catalog it, I figured it was worth my time to look at it.
And it’s a red-orange-gold gem that is a feast for the eyes. The secondary is a delectable dot of faint light, but is several magnitudes too dim for detecting color in the average sized back yard telescope. I’ve found it’s easily visible in everything from an 85mm to a six inch refractor. And a bit of averted vision in a 60mm f15 scope brought it into view several different times for me in a 20mm TV Plössl (45x), which will give you something to shoot for.
Haas doesn’t list this one in her book, and Admiral William Smyth apparently ignored it also. But William H. didn’t, and I haven’t, and if you like red or orange or gold in your stars, neither should you!
Σ 1834 HIP: 70066 SAO: 45000
RA: 14h 20.3m Dec: +48° 30′
Magnitudes: 8.1, 8.3
Position Angle: 104° (WDS 2011)
Distance: 232 Light Years
Spectral Classification: F9
But now we move on to some sterner stuff — perilously close points of dim light in a rarely traveled star lane. We’re going to bisect the Boötes club, so a short hop of two arc minutes due east with a slight bias to the south will take you through the lower third of it and just past its edge. This one can be tough to find — if you get lost, note that it forms an extended right angle triangle with 6.3 magnitude HIP 69862 and fifth magnitude HIP 69951, straddling the line that runs from Lambda (λ) to Theta (θ) Boötis. That trick has bailed me out on this one more than once.
And once you’ve found it, we’ve got some serious work to do.
When I first came across the numbers on this, I really doubted I would have much luck splitting it with anything short of six inches of aperture. My first try was with a Meade AR-5, which has five inches of glass, and much to my surprise, this pair rolled over and surrendered without a fight. In an 18mm Radian (66x) it was barely elongated, in a 14mm Radian (84x) it was clearly elongated, and in a 10mm Radian (118x) I found myself staring at a hair-split pair of subtle-hued yellow-white stars so close to each other that the black space between them almost wasn’t there. The always dependable 7.5mm Celestron Super Plössl carved a dark and definite slice between the stars and served them up on a velvet black background.
The subtle beauty of that view was absorbing, captivating, hypnotizing — a Star Splitter’s heaven even. A good comparison is the “B-C” pairing of Σ 761 in Orion as seen in a 60mm refractor. The magnitudes of that pair are similar, 8.4 and 8.6, but they’re much wider at 9.0″. In the 60mm lens, though, those magnitudes are dim enough to make them difficult to separate — so in that sense, the views are uncannily similar. More on Σ 761 and its brighter and more complex neighbor, Sigma (σ) Orionis can be found here and here.
Lured by the promise of that view, I returned the next night with my six inch f10 refractor for another small taste of heaven. This time the two stars were touching in a 14mm Radian (109x), elongated and trying to get free of each other in a 12mm Radian (127x), and split by a bit more than a couple of hairs in a 10mm Radian at 150x, as shown in the sketch. I had a more defined split in the 7.5mm Celestron Plössl (203x), which prompted me to try a 4mm AT Plössl. But at 380x those two eighth magnitude stars were having trouble squeezing enough photons through the pinhole on the field stop of the lens to illuminate the other end of it, so I went back to the 10mm Radian.
Now I’ve been back to Σ 1834 several times with smaller scopes since the observations described above, and I’ve found that under category III seeing conditions, I can split it in a four inch refractor. But it’s tight — you have to look very closely to get it, and there’s a limit as to how much magnification you can use before reaching the point where the light from the two stars becomes too faint to work with. I almost got it with a TV85 one night when seeing conditions were similar, but there was just too much movement in the eyepiece to be sure of it. It may be possible under much better seeing conditions.
But now that we’ve strained our eyes so strenuously on this closely separated pair of faint stars, let’s give them a rest and move on to something a bit more comfortable.
Σ 1843 HIP: 70447 SAO: 45045
RA: 14h 24m 39s Dec: +47° 49′ 50″
Magnitudes A: 7.7 B : 9.2 C: 9.7
Separation AB: 20.9″ AC: 98.9″
Position Angles AB: 180° AC: 59° (WDS 2011 for both)
Distance: 361 Light Years
Spectral Classification: F4
Σ 1843 is about three quarters of a degree to the south and east of Σ 1834 — and yes, it’s easy to get the numbers of these two stars mixed up. And I’ve found it can be a difficult one to locate as well, despite its short distance from our previous star. The best visual aid is to look at it as the first in a short arc of three stars — seen in the last chart above, or the one below– as you move slightly southeast towards it.
Now if you just happened to stumble across this compact little triple star without knowing what it was, you would probably make a quick mental note of it and keep going. But after I spent a prolonged period of time dissecting Σ 1834 in a very confined and restricted circle of space, this was really a welcome contrast — the difference was immediate and obvious. When my eyes took in the wider separations of the three stars, I felt like I was cavorting in an open field.
My first sighting of it was with the AR-5 in an 18mm Radian (66x). All three stars were easily seen, but I needed to look up the position angle of “C” in order to distinguish it from another star of similar magnitude located about the same distance to the northwest of the primary. The primary I saw as white, and I was able to pick out a slight tint of reddish-orange in “B” — no luck with seeing color in “C.”
At magnitudes of 9.2 and 9.7, the “B” and “C” components can be difficult to pick out in a 60mm scope. In the Lafayette 60/800 I have mounted on the AR-5, I needed to look closely with a 20mm TV Plössl (40x) to see the AB and AC splits. With a 15mm TV Plössl (53x), AB was a very tight pair and “C” almost faded from sight without the use of averted vision. I tried a couple of .965″ eyepieces in that scope and found I needed averted vision to separate “A” from “B” in an H20mm, but it was easy with direct vision in an HM12.5mm (64x).
I swapped those two little eyepieces into the AR-5 for a quick look and was really struck by the difference in the view. Everything I could see in the 18mm Radian was visible in the two .965″ eyepieces, but the tighter radius of the field pulled everything into a more compact circle, shrinking the already diminutive points of starlight as well. A different experience, but one worth repeating.
39 Boötis (Σ 1890)
HIP: 72524 SAO: 45231
RA: 14h 49.7m
Dec: + 48° 43′
Magnitudes: 6.3, 6.7
Position Angle: 45°
Distance: 229 Light Years
Spectral Class: F6, F5
Now we’ll leap about three degrees to the northeast and get clear of this club the Hunter is waving in the air and reward ourselves with a brighter and more colorful pair of stars. Draw a line from Σ 1843 so that it goes midway between 6.5 magnitude HIP 71235 and 5.7 magnitude HIP 71280 and it will take you right to 39 Boötis.
Admiral William Smyth approached it from Polaris, however, by extending a line to Beta (β) Ursa Minoris, also known as Kochab, “and prolonging it just as far again.” (The Bedford Catalog, p. 329) That works, although the distance from Polaris to Kochab is about fifteen degrees, and from Kochab to 39 Boötis is a bit more than 25 degrees. You’ll need dark skies to see it, however. Mine are normally dark enough that I can just pick it out with averted vision, but using the finder on the scope or a pair of binoculars is less strain on the old naked eyes.
As you’ll notice right away, this pair is considerably brighter than anything we’ve looked at so far. Two things add to its beauty — its color and the close separation of the two stars. Although, as Haas notes, they’re not too close for a 60mm scope:
Showcase pair. 60mm, 120x: A pair of touching twins, whitish gold in color, that are just bright enough for a 60mm to show them sharply.”
She credits Webb with seeing white in both stars, and Admiral Smyth saw white and lilac, which must have been his favorite color, one I have yet to see in a star. What I did see, though, was identical colors in both stars — gold with a slight tint of red. At any rate, the brighter and richer colors were a welcome sight in comparison to the prior stellar sightings.
My 60mm f/15 Carton lensed scope was just able to pry this pair apart with the aid of an 11mm TV Plössl at 82x, and at the time I tried, the seeing had started to deteriorate to the point that there was no sense in adding more magnification. I also managed a clean split in a TV85 with a 6mm Celestron Ortho (100x), but the advantages of aperture were apparent in the 152mm f/10 refractor. As the sketch shows, both components were clearly separated at 127x in a 12mm Radian. But it was their color that really grabbed my attention — a soft, glowing gold that gleamed against a very dark sky. If it hadn’t been for the vibrations caused by the seeing conditions, I almost would have thought I was looking at a painting. A real pleasure, especially after the dim terrain we’ve been picking our way through up until now.
And that pretty well puts a Star Splitter’s cap on a wonderful series of nights I spent searching this area. I must have gone back half a dozen times to look at these four stars with apertures ranging from sixty to two hundred millimeters, and to familiarize myself with the territory. I can throw away the map for it now — it’s imprinted so well in my memory, I should have no problem negotiating through it again in another month or so.
Thanks to the cooperation of the sun, we’re entering the time of year now when darkness begins just a bit earlier each evening — and that has the effect of almost suspending the westward march of the constellations since it’s possible to begin viewing a bit earlier each night. So Boötes will still be perched in the southwest shortly after dark, beckoning to me with his club.
And resistance is futile.