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Traipsing Through Triangulum Again: Six Trianguli, Σ 239 . . . . and Triangulum Minus

On our first foray into Triangulum, we took a hard look at Epsilon (ε) Trianguli, which we found on the north side of the Apha-Beta line.  This time, we’ll travel south of Triangulum’s Alpha-Gamma line and look at two contrasting pairs that offer plenty of relief for color-parched eyes.

Dial up a medium aperture scope – you can see both of the stars on this tour in a 60mm refractor, but you may find 80mm or larger is more to your liking – and take a look at the chart below to get your bearings.  (There is a wide angle chart of Triangulum here which will provide a larger context if you’re not sure where exactly to find Triangulum).

Six Tri is a short two degrees south by east from the Alpha-Gamma line, and Σ 239 is another two degrees beyond that, forming (of all things!) a triangle with 5.3 magnitude 10 Trianguli and 6.7 magnitude SAO 75269. But hold it – there’s one more triangle here, too . . . . . . .

.

In the 1600’s, there was another small constellation in existence known as Triangulum Minus, which depended on Six, Ten, and Twelve Trianguli for its corners …… except that they would have been known as Six, Ten, and Twelve Trianguli Minoris. Thanks again to Jim Kaler’s web site for that delectable morsel of information (link provided in the the first full paragraph below). (Stellarium screen images with labels added, click on either chart for a larger view).

Let’s start with a look at Mr. Flamsteed’s number Six ———

Six Trianguli  (Σ 227)  (Iota Trianguli)  (H II 34)  (SHJ 28)       HIP: 10280   SAO: 55347
RA: 02h 12.4m   Dec: +30° 18′
Magnitudes:  5.3, 6.7
Separation:   4.0″
Position Angle: 69°  (WDS 2011)
Distance: 305 Light Years
Spectral Classification: G0-G5, F5

——— which is easy enough to find, situated as it is southeast of and halfway between Alpha (α) and Gamma (γ).

The labeling of Six Trianguli can be a source of some confusion.  You’ll find it occasionally referred to as Iota (ι), as in Haas’s book, or in Admiral Smyth’s Bedford Catalog.  Chances are, though, you won’t find Iota on any of the commonly used star charts, such as Sky & Telescope’s Pocket Sky Atlas or The Cambridge Double Star Atlas, where it’s normally labeled as 6 Trianguli — a point also made by Jim Kaler in his detailed account of this star (which includes the reference to Triangulum Minus mentioned above).

I found this one first on a moon-free night in my six inch f/8 Celestron refractor, twinkling happily away at the center of the field in orange and gray:

Guaranteed to have you dancing under the moonlight! (East & west reversed to match the refractor view, click on the sketch for a larger version).

The primary was responsible for the orange (actually a pale orangish-white), and the secondary clung close by with a peculiarly vibrant white-gray tone to it.  And over at the northeast edge of the field, SAO 55358, a 7.8 magnitude K0 class star, added it’s orange tint to the overall ambiance of the field, providing an aesthetically engaging view in an 18mm Radian (67x).

I came back a week later with my Skylight f/13 100mm refractor on a night when a scurrilously bright moon was haunting the autumn evening, making it difficult to pick Six Tri out of the sky naked-eye wise.  I finally found it though, and with a 12.5mm Astro-Tech Plössl (104x) resting contentedly in the diagonal, I was treated to a thin black slice of sky between Six Tri’s 5.3 and 6.7 magnitude suns.

But the view that really had me dancing in the moonlight was the one I found in a 20mm Tele Vue Plössl (65x).  The gray-white secondary appeared as a mere dust mote of light nestled up against the orange-white primary – and both were floating in a moon-brightened void bracketed in one corner of the field by SAO 55358’s orangish rays and in the other by the white-like light of SAO 75186, which had stumbled into the picture before me from the southwest side of the field.  And the whole thing was framed magnificently by the eyepiece’s circular field stop, now made very visible courtesy of the moon’s autumnal glow.

Thrilled to my dancing toes as I was with that view – and exhausted, too – I decided to take a breather, have a seat, and see what I could see in the 60mm f/15 refractor I had resting along the spine of the 100mm refractor.  I bent down to my eyepiece box, came up with an 11mm Tele Vue Plössl (82x), leaned over its little lens as I brought the 60mm image to a focus – and gave thanks to my danced-out toes that I was sitting down.

What I saw in that 60mm 82x view was very similar to what I had just witnessed in the 100mm scope, but missing from it were the bracketing beams of SAO 55358 and 75186.  All alone in the center of the field were Six Tri’s two very delicate and now forlorn stars, crying out from their isolated black void for some careful visual attention.  Ah, the heart-rending aspect of it all!  It was more than I could bear in my worn down and danced out state of mind –– I went back to the 100mm view and an 18mm Radian (67x), and thanked it profusely for it’s wider perspective of the heavens.

Now the colors of Six Trianguli seem to be somewhat variable.  Haas’s 60mm report – “A bright grapefruit-orange star almost touched by a little gray globe” – is similar to what I saw, but Admiral Smyth described the pair as “topaz yellow” and “green.”  William Herschel, who discovered the dual nature of Six Trianguli on October 8th, 1781, recorded this description: “pale red or reddish white” for the primary, and “blueish red” for the secondary (1782 catalog, p. 68).   I suspect those colors have more to do with his speculum mirror, though, than anything else.  Burnham notes on p. 1896, Volume Three, of his Celestial Handbook  that the two stars have also been described as bright golden yellow, and sapphire and gold.

Sirs John Herschel and James South didn’t leave any comments on color for posterity, but they did describe them well here:

From page 52 of the Herschel/South Catalog of 1823, link provided in the last full paragraph at the bottom of the page.

And now a slight move to the south brings us to another one of Sir William’s discoveries ——-

Σ 239/STF 239  (H IV 40)  (SHJ 31)  (HJL 32)      HIP: 10680   SAO: 75265
RA: 02h 17.4m   Dec: +28° 45′
Magnitudes:  7.1, 7.8
Separation:  14.0″
Position Angle: 212°  (WDS 2010)
Distance: 113 Light Years
Spectral Classification: F5, G2

——- which also happens to be one of my discoveries.

I actually found this one quite by accident on the moonlight night mentioned above when I was  searching for Six with the 100mm f/13 refractor.  I couldn’t pry Six Trianguli out of the bright sky visually, so I estimated its position, aimed the scope, peered into the finder, and centered what turned out to be Σ 239 (STF 239).  It struck me as being a bit dimmer than what I thought Six should be, so I went back to the finder, caught sight of the triangular configuration mentioned in the caption of the first chart above, and realized the scope and I had wandered too far south.  A quick look at the S&T Pocket Atlas showed me what I had caught twinkling in the eyepiece was Σ 239, which was easy to identify because of it’s proximity to 10 Trianguli.

So as you can surmise, this pair is somewhat similar to Six – although on closer examination, the differences are very distinct.  Apart from the different position angles and separations, the colors are reasonably close, as you can see here:

Just enough yellow and gold to almost make orange! (East & west reversed to match the refractor view, click on the sketch for an enlarged version).

The components of the Σ 239 pair struck me as having the same light gold consistency, with traces of yellow and white visible at times – probably caused by the interaction of the primary’s yellow-white F5 light with the secondary’s yellow-leaning G2 rays.  Visually, they’re very similar in size, and with the bright background contributed by the moonlight, they were a bit haunting in the f/13 100mm refractor as they wavered and hovered slightly in the unsteady seeing.

If you back off to a wider angle view, you’ll find the east corner of your eyepiece decorated by 10 Trianguli, an A2 spectral class star which contributes a 5.3 magnitude shot of blue-white light to the scenery.  Try that in an 80mm rich-field refractor on a dark night not menaced with moonlight, and you’ll have a view that deserves to be etched in glass and hung on your wall.

William Herschel was here first, once again, catching his inaugural look at what he cataloged as H IV 40 on the same night he first saw Six Trianguli (October 8th, 1781), describing it as “the preceding of three telescopic stars” – which it is.  (p. 76 of 1782 Catalog).  John Herschel and James South took a look at this pair on December 15th, 1821, with a 3.75” Dolland refractor featuring a focal length of five feet.  They noted that Struve seemed to have confused Sir Williams’ observation of this star with 10 Trianguli, so they returned to the senior Herschel’s hand-written notes to see what they could find.   And what they found there was this — “preceding telescopic star of a small triangle, whereof the largest is 10 Trianguli.” – which is notably more precise than the printed version of the 1782 catalog quoted above.   (Source: pp. 54-55 of 1823 Herschel/South Catalog, scroll down to the the bottom of the screen)

Which clarified the confusion —— completely . . . . . . .

and just goes to show  ——-  anyone can get lost in the stars.

Next stop – a change of position eastward and a view of two very dis-similar Triangular stellar lights.

Cloud-free skies at night!   😎

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3 Responses

  1. What a fun post. I got out the other night and did a sketch of Struve 239 w/ my C925. Didn’t get as many stars as you did, though. Maybe my eyes were tired. :-] I may have gotten SAO 75269, though. Also a star to the east which can’t seem to identify but may be 10 Tri, but to the east??? Anyway the primary seems yellow/gold and the companion a bit bluish. I hope you can take a look at the sketch and let me know what you think of it. I measured it with my AM EP and got a Sep of 14″ and a P.A. of 211º!!! Getting a little better with this EP…

  2. Great work with the astrometric eyepiece, Steve! You pretty well nailed this one!

    I looked at your sketch — and there’s a good reason you didn’t get as many stars as I did. Your field of view in the C9.25 with the eyepiece you used is about 1/5 of what mine was in the six inch refractor!

    SAO 75269 was outside your field, and yes, 10 Tri is to the east. It holds down the east corner of the triangle it forms with SAO 75269 and Struve 239.

    There’s lots more in this little corner of the sky — hoping to get back to it tomorrow night.

    John

  3. Hi John!
    Whilst finishing up my imaging run in Triangulum, I took a moment to take in Six Trianguli (Σ 227). What a splash of colour. A veritable mini Albireo. For my eyes, the secondary was sapphire blue. This pair will provide for anyone with the time, a wonderfully colourful display. A real treat. I note that Steve and I get the same colour sensation for the secondary…so it must be so…LOL.

    Cheers, Chris.

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