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

Click to enlarge.

To begin with, I’m really not sure how H I 21 became confused with Σ 285 in the WDS, since William Herschel was very specific about its proximity to 12 and 13 Trianguli in the catalog description I included in part one.

Not only that – but on page seven of his 1827 Catalogus Novus Stellarum Duplicium Et Multiplicium, F.G.W. Struve explicitly linked H I 21 with his catalog number 269 (Σ 269).  And at the same time, he also made no mention of H I 21 in his listing for Σ 285.  If you click on the thumbnail image of page seven of the senior Struve’s book at the right, you’ll see the entry for his catalog number 269, and below is the entry for number 285:

In addition, H I 21 is also specifically identified with Σ 269 on page 67 of Thomas Lewis’s huge 1906 compilation of observations of Struve’s double stars, Measures of the Double Stars Contained in the Mensurae Micrometricae of F.G.W. Struve:

As I mentioned in part one of this twisted tale of suspense, if you look at the WDS “Notes file” for Σ 285, you’ll see this notation – “H 1  21” – but what really surprised me was what I saw in the “Notes file” for  Σ 269:  “STT  41. May also be H 1  21”.  (STT 41 is the same as OΣ 41 in the excerpt above from Lewis).

At any rate, it should be abundantly clear at this point that Σ 285 is not  H I 21.  More to the point, based on Wm. Herschel’s 1782 catalog description, plus Struve’s 1827 catalog entry, as well as Lewis’s 1906 compilation, it’s obvious that H I 21 is Σ 269.

HOWEVER –—  Σ 269 is itself surrounded by a puzzling Piazzi mystery boiling up and out of the excepts above from Struve’s and Lewis’s catalogs.

In case you didn’t notice, Struve associated Σ 269 and H I 21 with a star from Giuseppe Piazzi’s 1814 Palermo Catalog, namely P.  II. 93 (which you can see in the thumbnail image at the top right of this page) —— while in the excerpt immediately above, Lewis associated Σ 269 and H I 21 with a different star from the Piazzi catalog, Piazzi II. 89.

(Note:  Struve, Lewis, and Smyth used different formats to express Piazzi’s catalog numbers, but they still refer to the same catalog.  I’ll quote the format in use by each of them — just remember they’re interchangeable.  The key ingredients are the actual numbers, 89 and 93).

In other words, although we now know that H I 21 belongs with Σ 269, we have two conflicting reports as to which star Σ 269 is.   🙄

Admiral Smyth’s account of H I 21 in The Bedford Catalog doesn’t help with this confusion.  His account of H I 21 is actually titled “93 P. II. Trianguli” — but at the end of it, he throws a large wrench directly into the spokes, almost as an after thought:

While this was in the press, I learned that Professor Struve had discovered, with the gigantic refractor at Poulkova, that the neighbouring star 89 P. II was double; the components being of the 7 ½ and 8 ½ magnitudes, and 1 ½” apart.”  (p. 63 of The Bedford Catalog)

That newly discovered double star is the one Lewis described above as being independently discovered by Otto Struve, which Lewis also identifies as Piazzi II. 89 (same designation, different format once again) — as well as H I 21.

So now we’ve come to this:  for 93 Piazzi (93 P. II. or Piazzi II. 93), Admiral Smyth reported magnitudes of 6.5 and 10, and F.G.W. Struve reported magnitudes of 7.8 and 11;  for 89 Piazzi (89 P. II or Piazzi II. 89), Otto Struve reported magnitudes of 7.5 and 8.5, while Lewis reported magnitudes of 7.5 and 9.8  ——-  and  ——  all four of them equated their Piazzi catalog designations with H I 21!

Based on those reported magnitudes, it’s possible the two Piazzi designations, 89 and 93, refer to as few as two stars or as many as four stars!  Of course it’s also possible, given the relatively wide latitude of magnitudes reported in the mid-nineteenth century, that they’re the same star.

After I recovered from this surprising and unexpected convergence of confusion, it struck me that H I 21 was orphaned once again.   I decided my next move would be to find out exactly what stars were being referred to with the labels Piazzi II. 89 and P. II. 93.  And that took some real digging, believe me, because if Piazzi’s catalogs are in the public domain, I sure can’t find them – and I spent hours searching for them.

Eventually I stumbled across a book that includes a cross reference for some – not all — of Piazzi’s and Flamsteed’s catalog numbers: Taylor’s General Catalogue of Stars for the Equinox of 1835.0 from Observations Made at the Madras Observatory During the Years 1831 to 1842, which can be found here. One odd and potentially confusing aspect of this book which bears mentioning is that the introduction is numbered with Arabic numbers and the body of the text is numbered with Roman numerals.  But notice – this is a general catalog of star positions – and not a double star catalog.

Click to enlarge.

If you go to page XXIII of that book, which you can see if you click on the thumbnail at the right, and scan down the column farthest to the right, which is labeled “Piazzi”, you’ll find “89” almost exactly halfway down.  If you continue down five more entries, you’ll come to “93”.  Now, from “93” scan across to the third column from the left (Star’s Name) and you’ll see it says “13 Trianguli”.  So now we know that 13 Trianguli is the same as F.G. W. Struve’s and Admiral Smyth’s 93 P. II.

Go back up the right column to 89 Piazzi, scan over to the third column from the left, and you’ll find this: “Piazzi II. 89”.  Rats! – no cross reference to  Flamsteed or anything else we can use to match up with today’s catalog numbers.  But we do have magnitudes, right ascension, and declination numbers to work with.

So I looked at the coordinates for RA and Dec listed by Admiral Smyth for his 1834 observation of 93 Piazzi and found they match Taylor’s 1835 numbers – which confirms the star Smyth described as 93 Piazzi/H I 21 is 13 Trianguli, just as he stated it was: “The larger star is 13 Trianguli of Flamsteed . . . “.  (page 63)

But . . . . . . . what about 89 Piazzi?  Can we find a star that corresponds to that?

Let’s take a look at Taylor’s 1835 coordinates for this mini-triangle of confusion:

12 Trianguli                    RA: 2h 18m 31s    Dec: +28° 55’ 42”
13 Trianguli/93 P. II       RA: 2h 19m   9s     Dec: +29° 11’   6”
89 P. II                              RA: 2h 18m 32s    Dec: +29°   7’ 45”

Now, if we carefully compare the coordinates of these stars, we can locate 89 Piazzi precisely in relation to 12 and 13 Trianguli – and what we find is:

89 P. II is 1 second in RA east and 12 arc minutes north of 12 Trianguli —
and it’s 37 seconds in RA west and 3 arc minutes south of 13 Trianguli.

Can we plot 89 Piazzi on a current map of the sky with that information?

Here’s a chart showing the epoch 2000 coordinates of Σ 269, along with 12 and 13 Trianguli:

Click on the chart for a larger view.

If you go 12.5 arc minutes in declination north from 12 Trianguli, you come to Σ 269 – and if you look closely at the chart, you’ll see Σ 269 is just barely east of 12 Trianguli (as in 1 second)   ——–   and   ———

If you go 35 seconds in RA west of 13 Trianguli and 3.5 arc minutes in declination south, you’ll come to Σ 269 again! !!! !!!!!

Now the question of the proper motion of each of these three stars arises here, but suffice it to say their motion is negligible.  Those figures are available in the WDS for both Σ 269 and 12 Trianguli,  and figures for 13 Trianguli are available in the Bright Star Catalog.    And if you go back to the sketch of Σ 269 in part one, you’ll see there just aren’t any other stars in the vicinity that could be 89 Piazzi.  I’ve also added an STScI photo at the end of this post showing the same area.

So the inescapable conclusion is:

Σ 269 is 89 Piazzi II, or Piazzi II. 89, or P. II. 89, or 89 P. II  —–  it doesn’t matter how you say it, Σ 269 and that Piazzi scoundrel are the same star!

Which means we now we’ve reached this point:

  • Σ 285 is not H I 21
  • 13 Trianguli is Piazzi 93, and was identified by Struve and Smyth as H I 21
  • Σ 269 is Piazzi 89, and was identified by Lewis as H I 21
  • 13 Trianguli is NOT a visible double star based on my observations, and is NOT cataloged as a double star in the Washington Double Star Catalog
  • 12 Trianguli, with a separation of one tenth of an arc second and magnitudes of 5.4 and 7.9, does not match the descriptions of H I 21 provided by Herschel, Struve, or Lewis.

Conventional view — click to enlarge either image.

SO ——- the only possible match for H I 21 is  ——

Σ 269, aka 89 Piazzi!!!

You really, really have to wonder why so much confusion took place — after all, only one of the three stars in this triangular configuration at the east edge of Triangulum Minus is a visual double star.  No doubt there’s a logical explanation, but I have no idea what it is.  It’s possible there were errors in the Piazzi catalog.

At any rate – I’ve now found a home for  H I 21 , and I now know which Piazzi catalog number belongs with which star ——

Refractor view (Both STScI photos with labels added).

so maybe now I can leave the constricted confines of this constellation characterized by confusing triangular constructions.


Keep an eye out for a streak of light emanating from Triangulum – I intend to eject myself with enough force that I could well end up in the middle of a summertime constellation.

To clear and less confusing skies!  😎


2 Responses

  1. Hi John!
    Some real fine research there. I appreciate the co-ordination of all the data. It demonstrates graphically how things can quickly leave the rails. Thanks for the links to all those ebooks (catalogues). I’ve added them to my list of shortcuts. I’ve headed into Perseus for my next series of submissions. Some very neat star fields. Looking forward to your next tour.

    Cheers, Chris.

    • Thanks, Chris — very much appreciated, believe me.

      I hadn’t intended to stumble into a marathon research effort when I first came across Σ 285 and H I 21, but it was one of those things that just wouldn’t let go of me. Making sense of the Piazzi confusion was the biggest challenge. I’m still mystified that his atlas isn’t available in the public domain, at least as far I know. I’ve looked for it since I finished the post above, and still no luck with it.

      Looking forward to Perseus, a place I intend to spend some time once I get some clear skies.


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