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Theta (θ) Virginis (51)

Theta (θ) Virginis (51 Virginis)   (Σ 1724)   (AB is H III 50; AC is H VI 43)
HIP: 64238    SAO: 139189
RA: 13h 10m   Dec: -05° 32′
Magnitudes  AB: 4.4, 9.4    AC: 4.4, 10.4
Separation   AB: 6.4″           AC:  71.1″
Position Angle   AB: 342° (WDS 2012)   AC: 300° (WDS 2002)
Distance: 125 Light Years
Spectral Classification: A0

I came across this attractive little triple system one night after spending some time with Iota Leonis and Porrima.

Theta (θ) is between Spica and Porrima in this Stellarium screen shot of Virgo. See the chart below for a close-up of the area within the rectangle. (Click on this and the next two images for larger views).

As you can see on the chart above, it lies midway between Porrima and Spica, so it’s easy to locate.  The first time I viewed it, there was so much haze in the air that the colors were a pale imitation of themselves.    A couple of nights later, the haze was gone and I was thrilled to see that the colors had regained their luminous luster.  The primary is a bright white, while the 9.4 magnitude secondary has a slight yellow glow to it.

A closer view of the area surrounding Theta (θ). (Stellarium screen image with labels added.)

I was back once more on June 5th, 2010 — and so was the harassing haze.  In my 63mm Zeiss, “A” and “B” were easy to see, but “C” could only be glimpsed with averted vision at 53x.  And, as is frequently the case when a lot of haze is present, increasing magnification only made it more difficult to see the fainter star because it also magnified the glare from the brighter ones.   But I had the cure for that!  I switched over to a 152mm f/8 refractor — and just like magic, all three were clearly visible at 76x and 98x.

East and west reversed here to match the refractor view, click to enlarge.

If you can catch a night of  good transparency, this triple star system is a very rewarding visual pleasure and offers quite a contrast with the much brighter Porrima to the west.


5 Responses

  1. Feb 20th, 2AM — 30 degrees, crystal clear, and a waning moon at about 85% of full.

    I was out the previous night looking at Porrima and Saturn, and I remembered Theta Virginis was in the vicinity, but because the bright moon that was very close, I didn’t have any hope of picking it out of the glare.

    So later in the day I checked Stellarium and found Theta was located on a line drawn from Saturn to Spica, at about 1/3 of that distance from the beautiful ringed planet.

    Sure enough, when I looked in my 8×50 finder this morning, I could see both Saturn and Theta in the same field.

    Theta was actually better than I remembered it — I hadn’t looked at since June 5th of last year. I was using an AR-5 refractor (127mm fl, f9.3) with a 60/800 Lafayette refractor (with a Carton lens) mounted on it.

    In the AR-5 with an 18mm Tak (66x), “B” was hugging the primary very tightly, and “C” was swimming out there in space all alone. Despite the glare from the moon, both were easy to see. And because of the glare, the only color I could detect was white with a tinge of blue.

    I increased the magnification to 94x with a 12.5mm Tak, which was about the limit I could coax from the seeing. Still nice, and it put just a bit more distance between “B” and the primary.

    I had a 15mm TV Plossl (53x) in the 60/800 and, surprisingly, I could see “B” easier than the more distant “C”. I swapped the 12.5mm Tak (64x) into the diagonal and couldn’t detect any difference. “C” was just very difficult to see, even with averted vision, thanks to the nearby lunar light. But it also matched my observation above under darker skies with the Zeiss 63mm refractor.

    This is a curious triple — and I have to say, it has a subtle beauty all its own. It deserves more than a quick observation and a short post. I’ll come back to this one several times this spring.

    But this is why it’s curious: with a difference of five full magnitudes between the primary and “B,” you would expect that “B” would be the difficult one to see — because at only seven arcseconds away, it’s much closer than “C” is out there at its seventy arcseconds of distance.

    That five magnitudes of difference means “B” is one hundred times fainter than the primary (multiply 2.51 times itself five times to get that figure,which is 2.51 to the fifth power). But apparently the seven arcseconds of distance is just far enough to give it a fighting to chance to show itself.

    The reason that “C” is difficult to pick out of the glare becomes a bit more obvious when you continue this math exercise. There is a full six magnitudes of difference between “C” and the primary. When you do the math, that works out to a much larger figure of 250 (2.51 to the sixth power) — so “C” is 250 times fainter than “A” compared to “B” at 100 times fainter.

    In this case, even though “C” is ten times the distance (70″) that “B” is from the primary, it would seem that distance isn’t quite far enough to overcome the 250x factor in image faintness. So there is an inter-play taking place here between both distance and faintness.

    And if that math makes you faint, think of the distances — these three stars are shining back at us out there at a distance of about 125 light years. Which is 186,000 miles per second times sixty seconds times sixty minutes times twenty-four hours times 365 days times 125 years. I’ll let you work that one out. 😉

    And that is why I love the night sky! In addition to the compelling beauty, all those photons that come flying through the refractor lens and out the eyepiece are linked to the laws of physics and optics.

    When I see something hovering in the eyepiece under the intent scrutiny of my star-splitting eye that doesn’t quite make sense, a bit of effort to uncover the mystery always results in another bit of arcane arcana that I can file away for later reference.

    Sure beats being under warm covers at 2AM when it’s 30 degrees outside!

  2. I had the 63mm Zeiss out again early this morning and was mainly looking at brighter doubles with it, such as Castor, Algieba, and Porrima. And of course, Saturn was hovering just below Porrima, so I spent some time on it.

    The seeing was much better than I’ve had recently — Saturn was very rewarding in the Zeiss at 120x with a 7mm Nagler. So I thought I would try splitting Porrima with the 63mm scope — which didn’t seem likely, but you just never know.

    I got up to 168x using a 5mm Nagler, and it really wanted to come apart, but just couldn’t summon the energy to do it. It was hard to hold the image steady, though, so I stopped there. Higher magnification might have done it, but I’ll have to try that on a better night.

    So there was Theta, hovering out there all alone between Saturn and Spica. I slewed the scope south and dropped a 12mm Brandon (70x) into the eyepiece.

    At first, with my eyes having been blasted by the high-energy photons fired off by Porrima and Saturn, I couldn’t see either of the two faint components. I shifted my vision slightly to one side, and suddenly — poof! — just like magic, both of them popped into view. The view of the Brandon was matched by an 11mm TV Plossl (76x), so I worked up to a 9mm Nagler (93x) and stayed with it for a while.

    As I mentioned, and attempted to explain in the previous comment, what always amazes me about this star is the fact that the much closer “B” component (7″) is always easier to see than the more distant “C” (70″) even though there’s only one magnitude of difference between them.

    But what I really like about this triple star – and what keeps drawing me back to it – is it’s delicate quality. After your eyes are blasted by the brightness of Saturn and Porrima, looking at Theta is really a different experience.

    When you stare intently at Porrima for ten or fifteen minutes trying to pry it apart visually, it’s bright white light leaves a mental impression that makes Theta very faint in comparison.

    Each of the two components of Porrima shine at a magnitude of 3.5, which is really quite bright in a telescope — the primary of Theta is a bit dimmer at 4.4. Not a whole lot of difference it might seem, but it’s one star at a magnitude of 4.4 versus two bright stars at 3.5 — so there is a considerable visual impact from that combined brightness in relation to Theta.

    What that means is that as you first focus your eyes directly on Theta in a low power eyepiece, the two much fainter companions are invisible. Averting your vision brings them into view, but just barely, especially so in the case of “C”. Even with more magnification, “B” and “C” are still very small pinpoints of delicate light.

    One of the fascinations of viewing double stars is the various kinds of visual experiences you encounter. After looking at the brighter doubles — Porrima, Castor, Algieba, Mizar, etc. — a dim triple like Theta seems rather boring at first glance. But as you keep at this, you begin to realize it’s like discerning the subtle differences in eyepieces.

    There is an aesthetic quality to this view: “B” hugs the Theta primary closely, while “C” can barely be glimpsed hovering out there all by itself ten times farther away. The view in the 9mm Nagler at 93x was probably the best view I’ve had of this triple system, at least from the aesthetic standpoint. In the 63mm scope that magnification had the effect of accenting the delicate aspects of the entire visual experience. I found it appealingly attractive. 😉

    A year ago, when I first came across this system in the 63mm Zeiss, I had difficulty in picking out both companions, especially the more distant “C.” Last night, knowing what to expect, and working toward squeezing the best possible view out of the scope that I could, I spent a very enjoyable twenty minutes or so absorbing the delicately faint photons of those two companions hovering around their much brighter primary.

    Double stars are really like a fine wine. You start with the brightest and easiest to split, then slowly work your way toward the more difficult ones, and gradually you find yourself admiring the subtle aspects of the experience that went totally unnoticed in previous observing sessions. As with a good wine, it’s the subtleties that enhance the experience.


  3. Great report. Being able to spot those faint components in a 63mm is quite a feat. Tried Theta last night under light polluted suburban skies in my latest new toy…a $150 DS 2090AT-TC Meade 90mm refractor. The seeing was mediocre but was able to pick out B in the correct pa without prior knowledge. Best view was using the 9mm MA at 89x. Also visible with 6mm at 133x. Was unable to see B at 200x as the seeing would not permit it. I assume the lower magnification in the poor seeing concentrated the light of the dim secondary better making it easier to spot. Did not notice C but wasn’t looking for it. Based on the faint mostly averted view of B I doubt if it would have been visible under the conditions The latest WDS measurments for Theta AB are over 10 years old with mag 4.40 -9.39 , 6.9″ PA 324 degrees (1999).

    Clear skies,

  4. Thanks for the WDS info, Karl! I updated the information on the data line using the WDS info, and added the separation between “B” and “C”. The old info was from the Cambridge Double Star Atlas and was apparently a bit older.

    While I was doing that, I noticed that Theta is also one of the stars classified by Herschel, and carries his designation, H III 50.

    The “C” component is really the tricky one to see, as I’ve described in the previous comments, but you should be able to get it in the 90mm scope using averted vision. Might need a darker sky, though, so maybe some kind of filter to counter the light pollution will help.

    Clear Skies to you, also!

  5. 12:30 AM June 25th, 2011

    I came back again to Theta this morning in order to make a quick sketch of it, not that I really needed an excuse to take a look at the subtle beauty of this compact little system.

    It was me and my six inch f10 refractor tonight, and it was nice to have a bit of extra aperture since there was some haze in the southwest as I aimed the scope at Theta. A quick peek in the finder to center it, then a step over to the 18mm Radian (84x), and there it was again. Hadn’t changed a bit, of course, but the view was very comfortable and familiar — kind of like what you feel when you put on a warm sweater on a damp evening.

    I’ve described Theta “A” as white in earlier observations, but tonight it had a pronounced yellow glow. Good old “B” was right there where I remembered it, snuggled up tightly to the warmth of its larger sibling — and “C” just lingered out there in the not too distant distance, as if it was perfectly content to watch it’s two companions in their close comfort. In the six inch, it really wasn’t the challenge it’s been in smaller apertures.

    I have to say this is an addicting sight. It took a few observations of Theta before I warmed up to it, but now that it’s grabbed a firm hold on my Star Splitter affections, it just won’t let go. I’m afflicted.

    There’s an ethereal thrill here I wouldn’t miss for anything.

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