I’ve been sleuthing and slithering around in the dark in this serpentine sector of the sky for what now seems like the better part of a long, long time — in reality, it’s only been for a couple of normal length months that were stretched into extra length months by a stubborn string of uncooperative spring weather. Every time I’ve planned an exit from this region, I’ve heard the call or felt the lure of some new stellar delight, and there I am — stuck in the snake’s lair once more. But one way or another, I’m sliding south from here when I get this post done, provided I can get the serpent to look the other way long enough.
The first of the stars in this short tour shares its field with a ghostly ethereal presence, while the other is accompanied by two additional faint pairs of double stars that only emerge from hiding when adequate aperture is applied. Both were planned for appearances in other posts, but were shifted further back in the pecking order for various reasons, none of which I can remember any more. At any rate, it’s time to make amends to each of them.
Serpens Caput is where we’re going, and if you haven’t been there, here’s a chart that will orient you in relation to the surrounding constellations. Once you’ve carefully committed every star on that chart to short term memory (there might be a test before we get done here 😉 ), you’re ready to move on to the next chart, which we’ll use for hopping from the first star to the second:
OΣ 300 HIP: 76733 SAO: 101673
RA: 15h 40.2m Dec: +12° 03′
Magnitudes: 6.3, 10.1
Position Angle: 261° (WDS 2008)
Distance: 1059 Light Years
Spectral Classification: G7.5
First of all, let’s take a look at a few observations that are notable for what they didn’t see, or at least mention.
Johann Heinrich Mädler first observed and measured this star in 1844, coming up with a separation of 15.43” and a position angle of 261.2 degrees. Otto Struve was four years behind him in 1848, with measurements that averaged out to 15.20” and 261 degrees. And W. J. Hussey, who recorded all of this data on p. 132 of this book, made three observations in 1898 that averaged out to 15.32” and 261.2 degrees. Based on their position angles in comparison to the 2008 observation in the Washington Double Star Catalog (WDS), it’s obvious these two stars have barely moved relative to each other, if at all, since their 19th century observations.
Finally, Sissy Haas had this to say about OΣ 300: “125mm, 200x: Striking contrast for the separation! A bright whitish peach star with a little vaporish bump on its edge. At 50x, a bright white star [Chi (χ) Serpentis] is wide in the field.”
And here’s what I saw:
Now you’ll have to look at the southeast edge of the field to see OΣ 300 – it’s not at the center in this sketch. I saw the secondary as a bit more than Haas’s “vaporish bump,” but then I was using another twenty-seven millimeters of aperture – which may also account for why I saw the primary as a light, pale yellow, with a slight lean in the direction of white.
And over on the opposite side of our circular field of view, you’ll see the ghost-like glow of a galaxy that goes by the name of NGC 5970.
Now I knew it was there when I went in search of OΣ 300, and in fact, it was part of the reason I wandered into this area. But I wasn’t really sure I would see it. For the record, it’s magnitude is listed at 11.4, but it’s surface brightness (SB) is listed at 13.1. That last number is more significant since it measures the effect of spreading out the galaxy’s 11.4 magnitude light across it’s entire size, which is 3.0’ x 2.1’ – in other words, to the telescopically aided eye, the galaxy has the appearance of a 13.1 magnitude object, not an 11.4 magnitude object.
Even though I knew the galaxy was near OΣ 300, I wasn’t sure that I would be able to capture the two in the same field of view even if I did see it. The first night I went in search of it, I was using my five inch f/15 D&G refractor, and thanks to very good transparency, I was able to easily catch sight of it. After that, I caught it again in my six inch f/10 refractor, as well as in an eight inch Celestron Edge SCT. But on those last two occasions there was a lot of murky moisture in the air, which made it a real struggle to pick the galaxy’s faint glow out of the sky background — it had actually been easier to see in the five inch refractor because the transparency was so much better that night.
To see it, you’ll need a dark, moonless night, and at least magnitude five skies. I’m under magnitude six skies, and still I had to really look hard for it on the two nights of poor transparency. Using the light blue beauty of 7.4 magnitude SAO 101663 (HD 139609) as a guide, look about ten arc minutes to the southwest of it – and it helps quite a bit to move your scope back and forth just a bit to get it to emerge from the background. And use averted vision! You’ll never see it by looking directly at it.
And now we return to our regularly scheduled double star program. 😉
Using the chart above, slide down the serpent’s back past Delta (δ) and Alpha (α) Serpentis until you reach Epsilon (ε). Two degrees to its south, you’ll see Omega (ω). You’ll find our next star, Σ 1987, sitting at the eastern corner of an equilateral triangle it forms with those two stars.
Σ 1987 (H III 103) (Sh 212) HIP: 78134 SAO: 121277
RA: 15h 57.2m Dec:+ 03° 24′
Magnitudes: 7.3, 8.7
Position Angle: 320° (WDS 2010)
Distance: 430 Light Years
Spectral Classification: A0
This is another star with a history, and like the previous one, it’s not standing alone in its field either – but this time, it’s a pair of double stars that provide the accompaniment, not a galaxy.
I first came across this pair when I was using an AT90mm f/6.7 refractor, which rewarded me with a delicate view of a light gold primary tinged with a bit of white, and a secondary that was a mere dot of surprisingly blue light. I didn’t expect either the color or the small visual size, mainly because there are only 1.4 magnitudes of difference between the two stars. I was also able to pick both stars out of the sky with a 63mm Zeiss refractor and a 15mm TV Plössl, so it’s not a particularly difficult pair to see.
But that night I also spied a pair of suspiciously close stars about four arc minutes northeast of our main attraction, which I eventually identified as TOB 255 (magnitudes of 12.0 and 12.9, 14.9”, and 198 degrees, WDS 2000). In the process of establishing their identity, I also found there was a second pair of doubles about 11.5 arc minutes to the west of the Σ 1987 pair. I had seen them as a single star in the ninety millimeter scope, so I returned with a six inch f/8 Celestron refractor in my hands and pried the dim little devils apart with the greatest of ease. That pair is BAL 1410, shining weakly at magnitudes of 11.18 and 11.20, closely separated by 8.1”, and parked at a position angle of 68 degrees (WDS 2000). Apparently they were just close enough that I couldn’t detect them as a pair in the 90mm scope at 60x. What’s surprising is that I could split the first pair, which are a full magnitude fainter, in the 90mm scope, but not BAL 1410. Either that extra six arc seconds of separation made a significant difference, or the first pair is brighter than the 12.0 and 12.9 magnitudes listed for it.
Just to provide a sense of the different perspectives provided by the two scopes, I’ve included sketches made with each of them:
And again, as with so many double stars, Sir William Herschel was here first. He found the Σ 1987 pair on March 4th, 1783, measured them at 12.5” apart with a PA of 320 degrees, and described both as red, although he qualified that with this: “a dry fog, if I may call it, probably tinges them too deeply.” (p. 197 of 1784 Catalog)
His son, John Herschel, and sometimes observing companion James South, observed the pair in 1823 on three occasions – May 21st, June 6th, and June 12th – and came up with 10.66” and 323 degrees, but left no comments on color. Friedrich George Wilhelm von Struve observed them in 1831 (10.27”, 324 degrees) and described them as white and ash, and Admiral Smyth caught them in 1835 (10.5” and 324.7 degrees), and saw white and gray. (Sources: Herschel/South Catalog, pp. 239-240 — scroll to the bottom of the linked page; Struve, p.434 of this book; Smyth, p. 350 of The Bedford Catalog)
Sissy Haas also had a look at these two stars in a 125mm scope and caught sight of the same colors I did: “A pretty pair that seems to jump out of an empty field. It’s an amber yellow star with a tiny blue companion just a small gap apart.”
And so …………. I think that’s mainly about it for Serpens Caput for a while since I’ve been detained here longer than I ever thought was possible. Although I’ve enjoyed every minute spent here, it’s time to move on — there are new paths calling to me from remote areas of the heavens not previously penetrated by me and my telescopic companions, and my focus fingers are twitching in anticipation.
But, but, but …………… before we go, it’s worth a short look back at this constellation. I took a tour the other night of all the stars I’ve visited the last few months and found it was a very satisfying way to spend an evening. I started at the southwest corner with a four inch refractor and picked off one star after another as I worked my way north and east, lingering over each until my eyes had their fill. Altogether, I suppose I spent about an hour.
I’ve attached a chart below which shows all those stars, and beneath it I’ve listed each of them, including separate links to both the original post and the individual sketches, along with a comment on the minimum aperture needed to see them – depending on your sky conditions, you may need a little bit more or a little bit less. There are two or three there that are beyond the reach of a four inch (100mm) refractor, but most of the others can be seen in apertures as small as 60mm.
So give it a try some evening. It’s a great way to get acquainted with a small section of the sky, and experience a very enjoyable evening while doing it. Highly recommended!
Clicking on the name of the star will get you to the post on it, and clicking on the minimum aperture will take you to a sketch of it:
49 Serpentis: 60mm for AB, probably at least 70mm for C
Σ 2007 (STF 2007): 60mm
OΣ 303 (STT 303): 127mm, maybe in a 100mm scope under ideal conditions
Σ 1988 (STF 1988): 100mm, but much less struggle in 127mm
39 Serpentis: 80mm, but you can catch the secondary in a 60mm with averted vision
Beta Serpentis: 60mm (you’ll need to use averted vision for the AB pair)
OΣ 300 (STT 300): 70mm, possibly 60mm under ideal skies
Delta Serpentis: 60mm
Σ 1987 (STF 1987): 60mm (Sketch 1; Sketch 2)
Σ 1930 (STF 1930) / 5 Serpentis): 70mm for AB, 60mm for C and D
Bu 32 / 6 Serpentis: 127mm
Bu 943: 152mm (on a night with stable seeing!)
Happy sleuthing, and Clear Skies! 😎