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Triangular Tribulations in Triangulum — Σ 269: Or How I Found the Real H I 21, and learned to like it. Part the First.

Trapped in Triangulum I am.

I entered this constellation innocently enough through the Epsilon Portal, then worked my way into the warped web of Triangulum Minus with the most positive of intentions, and eventually attempted an exit in an easterly direction —– but ran head first into a mysterious wall at Σ 285 with a resounding clang that is still probably sending shock waves throughout the seven hundred light years separating us from it.

If this isn’t the galaxial equivalent of the Bermuda Triangle, it’s a darned good imitation.

And all I really wanted to do was go to Taurus.

Maybe I can talk my way out of here if I explain what happened.


The venerable Admiral led me into this labyrinth.

It started with Σ 285, aka STF 285, aka H I 21 – that last label being Sir William Herschel’s 1782 catalog number.  The Roman numeral “I” is Sir William’s designation for a “difficult” star —– “difficult” definitely being an understatement in more ways than one.  (You can find a concise description of Wm. Herschel’s catalog designations on page four of The Cambridge Double Star Atlas).

I first found the H I 21 designation for Σ 285 in the Washington Double Star Catalog (WDS), but mystification materialized from out of the metaphorical blue when I cracked open my copy of the Admiral’s ever-dependable, always reliable Bedford Catalog, where you’ll find H I 21 described under the heading “93. P. II. Trianguli” (the “P.” refers to Guiseppe Piazzi’s 1814 Palermo Catalog, which we’ll return to later).  He described the colors as yellow and gray, estimated their magnitudes at a very surprising 6.5 and 10 (those of  Σ 285 are actually 7.5 and 8.1), and adds:  “This exquisite and difficult object was discovered by Herschel in October, 1781, being No. 21 of the First Class.” (p. 62)

OK so far.  But THEN he captured each and every single scrap of my attention with this comment on page 63: “The larger star is 13 Trianguli of Flamsteed . . .” —- and THAT star just happens to lie at a significantly distant four degrees southwest of Σ 285, where it spends all its time guarding the eastern edge of Triangulum Minus, as you can see here.

So, confronted with a contradiction, I returned to the birthplace of the H I 21 designation, page 62 of Sir William Herschel’s 1782 Double Star Catalog, where I found this entry:

21. c Trianguli, near FL. 12. and 13.
Oct. 8,        Double. It is the most north of a small telescopic trapezium of
1781.         unequal stars. Extremely unequal. With 460[x], [the small star is] ¾ diameter of L[arge].  Position (by estimation) 55° or 60° n. preceding.”

Now not only did I find mention of 13 Trianguli, but 12 as well (Fl. 12) – and in fact, 12 Trianguli is the star being guarded by 13 Trianguli at the eastern edge of Triangulum Minus.

So at least I knew this much now – H I 21 does NOT refer to Σ 285.  That much was glaringly obvious anyway from looking at the Admiral’s estimated magnitudes of 6.5 and 10.

What exactly, then, does H I 21 refer to?  Against my will, I felt myself being dragged back into the bizarre world of Triangulum Minus.

If you go back to Herschel’s entry for H I 21, that first line —  “c Trianguli, near FL. 12. and 13.” –  seems to be saying H I 21 is ““c Trianguli.”  So I found myself wondering what star Sir William was referring to with the “c Trianguli” designation.

Since Flamsteed is mentioned (that’s what the “FL.” stands for in that line), the logical thing to do is go to the same atlas Herschel used, Flamsteed’s Atlas Coelestis, which can be seen here. (Click on “Map of constellation Aries”, enlarge it to 100% and depending on your screen display, either pan back up once or pan to the right once by clicking on the up and/or right arrow to the right of the window showing the enlargement percentage).  When you find Triangulum near the top of the page, you’ll see the outlines of two triangles – the large on is Triangulum as we now know it, and below it, there’s a smaller one, which is Triangulum Minus.  If you look at the far left corner of Triangulum Minus, you’ll see a star that’s labeled with a “c” – and that particular star is Flamsteed’s 12 Trianguli.  (You can compare that against our earlier chart here).

So now we know “c” and 12 Trianguli are the same stars.  But why refer to the same star twice with two different designations (“c Trianguli, near FL. 12. and 13.”), and how can it be “near” itself???

Flummoxed into a Flamsteed-like fog, I checked the WDS to see what I could find on 12 and 13 Trianguli, and discovered 13 Trianguli is not shown as a double star, but 12 Trianguli is —— except that it’s 5.4 and 7.9 magnitude stars are separated by one tenth of an arc second and were discovered in 2003, cataloged as YSC 1, and not measured since.

So – since 12 and 13 Trianguli are not double star candidates for Herschel’s H I 21 label, let’s focus our lens on this: “near FL. 12. and 13.”

If you turn to chart number four of Sky & Telescope’s Pocket Sky Atlas, you’ll find an unlabeled double star wedged tightly between 12 and 13 Trianguli (don’t bother with The Cambridge Double Star Atlas, which doesn’t show it), and with the aid of MegaStar, I discovered that particular double star is Σ 269!

Aha!  So have we found the real H I 21?

Maybe.  Maybe not.  Don’t expect things to be simple in the Bermuda Triangle.

First, let’s look at the current WDS numbers for Σ 269 so we can see what we’re dealing with:

Σ 269  (STF 269)                HIP: 11490   SAO: 75383
RA: 02h 28.2m   Dec: 29° 52’
Magnitudes: 7.59, 8.97
Separation:  1.6”
Position Angle: 345°  (WDS 2008)
Distance: 620 Light Years
Spectral Classification: G0

And even better, let’s go see what it looks like:

Σ 269 was positioned at the top right quadrant of this view in order to include 12 and 13 Trianguli in the field. (East & west reversed to match the refractor view, click on the sketch to get a better view of  Σ 269’s elusive secondary).

I managed to fish this thing out of a turbulently murky sky with something bordering on a maniacal effort.  I would have preferred a better night for prying apart a pair of stars separated by a tight 1.6” with 1.4 magnitudes of difference, but I was fortunate to have the few hours of clear sky I found —- so I decided to persevere and settle up with the sky gods later.

I included 12 and 13 Trianguli in the sketch above so you can see how Σ 269 is positioned in relation to them.  If you remember, Herschel described H I 21 as “the most north of a small telescopic trapezium of unequal stars. Extremely unequal.”  And you can clearly see that’s the case if you include either of the SAO labeled stars as the south corner of the trapezium.

And he describes the position angle this way: “Position (by estimation) 55° or 60° n. preceding.”  When those numbers are translated into modern day terms (there’s an excellent conversion chart on page x of the introduction to The Bedford Catalog), his estimated position angle is 325° or 330°, which puts it in the neighborhood of the 2008 WDS measurement.

The main thing to be aware of before we proceed any further is that 12 and 13 Trianguli have no visible companions.  I put each of them, along with SAO 75389 and 75390 under my six inch telescopic microscope, running the magnification up to 304x with a 5mm Radian in the merciless murk – and I can safely say not one of those four stars has a visible companion in the neighborhood of the 1.5” to 1.6” range that is brighter than tenth magnitude.

So at this point we know what H I 21 is not – it is NOT Σ 285.

Could it be, then, that H I 21 is Σ 269?

This is a good place to pause, take a deep breath, pour a suitable liquid into a cup or a glass, and get comfortably situated for the next surprising twist in this tale of triangular confusion.  Once you’ve wriggled into your chair and propped up your feet, click here to take the next leap.


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