• Choose a post by category or constellation

  • Learn the Night Sky

  • Search strategies

    Use the Search box below to find doubles by popular name, RA, or telescope size. For example, a search on "15h" will find all doubles we've reported on that have an RA of 15 hours. A search for "60mm" will find all doubles where we used that size telescope.

Traipsing through Triangulum with Epsilon (ε) Trianguli

So what exactly are we doing up here, suspended in this dinky little three-sided constellation wedged between Andromeda and Aries, Perseus and Pisces?

Well, it’s like this — I’m re-paying an old galaxial debt.  For too long, I’ve ignored the Alpha (α), Beta (β), and Gamma (γ) of Triangulum — and everything in between and beyond, at least with regard to double stars.   I guess it’s because I’ve always thought of galaxies when I’ve contemplated Triangulum.  Not only does the third largest member of the Milky Way’s Local Group, the spectacular M33, reside in Triangulum, but there are also quite a number of very faint galaxies hiding up here, many of them so close together you can see several at once in a field only thirty minutes of arc in diameter.  Of course, you need a lot of telescope for that, but a ten inch or larger will net you enough of them that you can subsist for several days.

But there be double stars scattered up here also amongst these shining suns of Triangulum — and some pretty darn good ones, too — and — weather permitting and Sky Gods relenting — I intend to make several long term acquaintances.

Follow me if you dare — it’s not like we’re going to get lost in this small corner of the sky.  And anyway, Andromeda and Perseus will keep a close eye on us.

First, a navigational chart – you can’t sail the skies without one:

Epsilon (ε) is easy enough to find — just look about a third of the distance along the line separating Alpha (α) Trianguli from Beta (β) Trianguli. (Stellarium screen image with labels added, click for a larger view).

Our first foray into the double star population of Triangulum requires five or six inches of aperture, a well-tuned Star Splitting eye, stable seeing, and at least average transparency – not a lot to ask for two or three times a year, is it?

Epsilon (ε) Trianguli   (6 Triangluli)   (Σ  201)          HIP: 9570   SAO: 55218
RA: 02h 03.0 m   Dec: +33° 17′
Magnitudes: 5.4, 11.4
Separation:  4.2″
Position Angle: 119°   (WDS 1990)
Distance: 370 Light Years
Spectral Classification: A2

What we’re dealing with here primarily is a wide magnitude gap aggravated by a tight spatial gap.  In other words, this one is a tough one.  In his account of Epsilon (ε) on page 48 of The Bedford Catalog, Admiral William H. Smyth notes that its discoverer, F.G.W. von Struve, described it with the adjective “difficilis” in the 1827 Dorpat Catalog – and you don’t have to be a Latin scholar to know what that means.  (In the link to the Dorpat catalog, click on the box to the left of “Go”, scroll down to “Section 22-6,” click “Go,” and Σ 201 will come up as the first entry on the page!)

My figures show the seven magnitude difference between the two stars results in the secondary being fainter than the primary by a factor of 2.517 , which in the plain language of Arabic numerals means “B” is 627.647857 times fainter than “A.”  Throwing out the decimals only makes it worse: 628 times fainter.  Throw in the always-hard-to-fathom distance, which in this case is a particularly prickly 4.2 seconds of arc – and you’re in for a long night if the Sky Gods aren’t on your side.  You might have to sacrifice one of Tele Vue’s new Delos eyepieces to those guys to get enough stellar dispensation to guarantee success.

On my first outing with Epsilon (ε), things were looking precariously unlikely.  I had armed my most effective Star Splitting weapon, a six inch f/10 refractor, with a variety of eyepieces before I finally settled on a 9mm UO Ortho boasting of 169 x’s.  The seeing was a very uncooperative II, but it was teasing me with an occasional flash of III, so I sat still and waited for my moment.

And waited.  And waited.  And waited.  A long, long wait it was.

Now you can’t succeed without the pertinent level of patience — but my patience needle had just about pegged all the way over to empty when I saw that first spark of secondarial light.  It was brief, but it was convincing:

Look quickly before it disappears! Note the rather close bonus double over there on the far east side of the field, SEI 21. It boasts magnitudes of 10.7 and 11.1, with a separation of 8.9″ at a position angle of 79 degrees (WDS 2010) — and you’re likely to see interstellar space between its components before you catch sight of Epsilon “B.” (East & west are reversed in this sketch to match the refractor view, click on it for a large version).

So I sat some more and waited some more — and then it flashed me again.  I held my breath, saw another flash, and then suddenly the seeing flattened out at III and I found myself engaged in a staring match with a very, very delicate spark of light — for about ten seconds or so.  And that was it.  It was gone, gone, gone.

But that tantalizing spark of almost white light danced hauntingly in my memory for three weeks — so on the first clear moonless night, I returned to the scene of the Long Wait.  And as I’ve found so frequently in these delicate battles of photonic wits, the secret is in the focus.  It has to be precise.  In fact, precise really isn’t even the right word.  It has to be better than that.  Excruciating comes to mind, but it doesn’t quite pin it down either.

I wasn’t succeeding with the 9mm Ortho, so I tried an 8mm Radian (190x) — no luck;  a 7mm Ortho (217x) — none again;  a 6mm Plössl (253x) — and again none.   So I reversed direction and tried a 10mm Radian (152x), fidgeted with the focuser for several seconds, and suddenly my lost long friend was staring back at me again.  I barely touched the fine focus knob — and he was gone.  I coaxed it back carefully — and there my sparky friend was again.  I did that a couple of times on either side of the critical  focal point — and I could swear there was a range of about one millionth of a millimeter in that fine focus knob where the spark-like “B” consented to an appearance.   I did the same thing with the 9mm UO Ortho, with the same results.

I’ve been back a couple of times since, but my sparkling friend has been absent every single time.  No doubt the mirthless and murk-full skies have something to do with that – but I’ll catch him again before he slides over the western horizon in the spring.  And when I do, I’ll keep a close eye on him until dawn if he’ll agree to stick around that long.


Permit me to provide a tip on this one, because it’s deceptively difficult:  what you’re looking for is a very, very weak glimmer of light right next to the primary.  And when I say very, very weak, I mean almost invisible.  If you’ve ever seen Polaris’s secondary in a 60mm scope at about 45x, its secondarial beam of subdued photons is about five or six times stronger than that of Epsilon “B.”   Seriously.   If you succeed in seeing Epsilon “B”, what you’ll see is so faint you’ll doubt you’re actually seeing it.  But it offers such a remarkable contrast in size and illumination to the yellowish primary, it’s well worth the search.  It truly is one of the most amazing and different kinds of views I’ve seen in the last few years.


So  . . . . .  all things considered, not at all a bad introduction to the duplicitous side of Triangulum.

Coming up next is a pair of colorful pairs on the south side of this three-sided configuration in the sky.

Stay tuned . . . . . . and Clear Skies!   😎


2 Responses

  1. Hi John!
    A wonderful uncluttered description of the process and patience required to observe one of these fainter denizens of the night sky. I took your side bar into the Bedford Catalogue authored by Admiral William H. Smyth and read the exerpt for the Orion Nebula. Now that is a book worth having on your shelf…kind of what I appreciate about your blog…personal with a wealth of information. Great stuff.

    Cheers, Chris.

    • Thanks once again, Chris.

      Yes, The Bedford Catalog is unique — there’s nothing else quite like it in 19th century astronomical literature. Maybe the best way to describe it is as that century’s version of O’Meara’s first couple of books, or as an expanded version of Walter Scott Houston’s observational writing.

      In addition to double stars, it includes a wide-ranging choice of “spiral nebulae” (we call them galaxies now), conventional nebulae, and open clusters. Well worth spending some time with on a rainy night . . . just don’t fall asleep reading it. 😉


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: