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Surrounded by a Ring of White Fire: Delta (δ) Herculis

Delta (δ) Herculis is shown here just to the right of center. You’ll have to use a bit of imagination to visualize Hercules standing on his head, with Rasalgethi marking the location of one eye. (Stellarium screen image with labels added, click to enlarge).

As the long twilight of a summer evening slowly yields to darkness, if you face south and cast an eye high up into the sky west of Vega, you’ll find yourself looking at the familiar keystone asterism at the center of Hercules.  Halfway between the southeast corner of it and Rasalagethi, you’ll find a fairly unremarkable looking whitish third magnitude star that’s about where Hercules’ left (eastern) knee should be — except that it’s really Hercules’ right shoulder because the poor guy is situated with his head pointing south towards Ophiuchus, not north.

But — if you point a telescope of eighty millimeters or more at Delta (δ) Herculis on a dark, moonless night, you’ll find yourself looking into the center of two concentric rings of white stars with a glowing ball of whitish light and just a dot of a secondary sitting in the center.

And  …  it  …  is  ….  ….  ….  magnificent!

Delta (δ) Herculis  (Σ 3127)    HIP: 84379     SAO: 84951
RA: 17h 15.0m   Dec: +24° 50′
Magnitudes     AB: 3.1, 8.3   AC: 3.1, 10.5   AD: 3.1, 10.6
Separations    AB: 12.3″       AC: 173.8″       AD: 191.6″
Position Angles   AB: 288° (WDS 2010)   AC: 357°  (WDS 2009)  AD: 93°  (WDS 2009)
Distance:  78.5 Light Years
Spectral Classifications:  A3 for each component

In this STScI photo of Delta (δ) Herculis, the central glow and the inner ring of stars is obvious. The outer ring is a bit subdued, but is easier to see if you click on the image and enlarge it. The secondary is lost here in the glare of the primary. (East and west are reversed in this view).

What struck me on my first look at Delta (δ) was how bright the field of view is.  The white light of the primary, at a magnitude of 3.1, is the chief cause of that impression, but it’s helped quite a bit by the north edge of the outer ring of stars, which are almost a full magnitude brighter than those in the inner ring.   (You’ll notice the outer ring is not quite complete, but like a lunar crater missing a part of its rim, your imagination easily fills in the gap).   Adding to the brightness of this image is the glow in the inner ring which is contributed by the gleaming primary.  And the final touch to this impression of a ring of fire is that most of these stars are barely varying shades of white.

This sketch does a better job of conveying the visual impression at the eyepiece, although it lacks the glow within the inner ring. East and west reversed, click to enlarge.

This sketch does a better job of conveying the visual impression at the eyepiece, although it lacks the glow within the inner ring. East and west reversed, click to enlarge.

I’ve included both a photo of the area, as well as a sketch, in hopes that you can mentally put the two together and get some idea of the effect of this configuration of stars.  The photo is a bit misleading because it includes fainter stars than you’re likely to see, and it loses some of the effect of the outer ring, but it does show the glow within the inner ring rather well.  The sketch at the right is a better rendition of the configuration of the stars that your eyes will actually see.   Missing is the silence of the view, along with an intangible quality which was alive at the eyepiece — a quality that words simply cannot begin to touch.

Below is a more recent sketch, which very effectively captures the glow emanating from the primary.  When you narrow the field to the point where the outer circle of stars is right at the edge of the eyepiece field of view, the effect can be both very hypnotic and overpowering:

Notice how large an area is covered by the flow of the primary.  It literally reaches all the way to the stars of the inner circle, and even extends past them in a few cases.   That's one heck of a lot of bright white light!  (East & west reversed here, click for a larger and better view).

Notice how large an area is covered by the flow of the primary. It literally reaches all the way to the stars of the inner circle, and even extends slightly past the “C” companion. That’s one heck of a lot of bright white light! (East & west reversed here, click for a larger and better view).

As you can see from the STScI photo and the two sketches, there is a lot of light here competing for your attention.  After your eyes have roved around the field of view for a bit, if you can get them to settle at the center, take a long, hard look at the two stars that are the main attraction.  I’ve described the primary as white, but there actually is a very slight touch of yellow in it, enough to soften some of the harsh light just a bit.  The secondary is a mere point of much paler white light, but it’s nestled up very closely to the primary, and depending on what aperture and what magnification you’re using, you may have to look very closely to see it at first.  The spacing between these two stars, and the physical appearance of the secondary in relation to the primary, is very similar to Polaris.

Now no matter how long I spend looking at double stars and reading the literature about them, I’ll never cease to be amazed at the variety of colors other people see.  Haas saw the primary as “Sun yellow” and the secondary as “whitish powder blue.”  But at least we’re reasonably close, especially in comparison to Admiral Smyth’s  description of “greenish white” and “grape red.”   I don’t know what to say about that, except that I sure would have liked to have had an hour or two with that 5.9″ refractor he used.

There are two more companions, “C”and “D,” which can be found lurking in the inner ring, both of which are apparently optical only, meaning not gravitationally linked to the primary.  The primary itself is actually two stars separated by a mere .06 of an arcsecond, requiring far more sophisticated equipment to detect than most of us have ever dreamed of using.  More along these lines can be found in Jim Kaler’s description of Delta Herculis.

As for the equipment most of us are more likely to possess, I’ve found the ideal aperture for Delta (δ) is about four inches.  My first view of it was in a 102mm Celestron f10 refractor using an 18mm Radian (56x), and it was perfect for capturing the full visual impact of all that white light which invades the field of view.  To get the full effect of both the inner and outer circles, use a magnification that puts the north edge of the circle almost at the edge of your field of view while Delta “A” and “B” are at the center.  As you increase the magnification and narrow the field, you begin to lose some of that impact, so don’t get too carried away unless you want to create a driving lane between the primary and secondary — which is well worth the effort if seeing conditions permit.

For a visual challenge, try a 60mm refractor — I found an f15 version would provide just a glimpse of the secondary at 45x, using a 20mm TV Plössl, which is pretty similar to what you would see if you were looking at Polaris.  The main difference is the Polaris primary has a distinct yellow tinge to it, whereas the Delta primary shows far more white.  Or at least it does unless you happen to be peering into Admiral Smyth’s 5.9″ refractor.

Now the cumulative visual impact of all this white light populating my eyepieces and saturating my sight was a bit of philosophical reflection about their attraction, as well as some thought about what these stars truly are.

What they truly are is a vast assemblage of nuclear furnaces — something Greg has pointed out numerous times.  They may not look the least bit lethal from your perch behind a scope, but if you ventured too close to any one of them, the result would be quite a bit more than singed eyebrows or fried fingers.  The indisputable fact of the matter is these beautiful stars and their immediate surroundings are tremendously harsh environments.  But — as frequently happens when I bend over the eyepiece and focus my eyes on these unimaginably violent objects that I see as bright or dim points of light, my aesthetic experience of them is far removed from the physical and objective reality.

While words are fine for describing the physical aspects of these stars, they don’t work well for describing the aesthetic experience.   I’ve half jokingly, half seriously, used the phrase “nourish your neurons” in hopes of getting at the inner depths of what happens within us — yet it still doesn’t quite convey its essence.  Something essential, something that reaches very deeply into our present, into our past, and into the very core of our being, takes place.  It’s not quite accurate to describe it as mystical, because it’s real — it’s just that it happens outside of language.  A far better descriptive word for what takes place is ineffable.

So it comes down to this:

There’s a very definite division between describing the objective physical facts of what we see, and conveying the full subjective impact of it.   And yet  …..  the two experiences are inseparably intertwined with each other.  Together they make possible what we experience, an experience as various as the number of people on this unique planet who peer into eyepieces.

There’s a paradox hard at work here, which is this:  these stars are both physically lethal and aesthetically beautiful at the same time.  And there’s a miracle here as well, which is the mere chance that any one of us happens to be in the right place and time to intercept those few photons which trigger this difficult to describe aesthetic experience.  The paradox was described almost a hundred years ago by Ranier Maria Rilke in his First Duino Elegy: “For beauty is nothing but the beginning of terror, yet still we endure it; and it dazzles us so because it scorns to calmly destroy us.”  A bit severe perhaps for our purposes, but only because of the distances involved.  But it does convey the paradox rather well.

And that leads to the rousing conclusion of this discussion of the nature of stellar attraction:

There  is  a reason the chicken crossed the road.  He was curious.  And so am I.  But in my case the road is metaphorical — so I won’t get run over, I won’t singe my eyebrows, and I won’t fry my fingers.  Which is fortunate, because I’m drawn to these pinpoints of light like a moth is to a flame  — or in my case, multiple flames.

So if you’ll excuse me now — and pardon the digression into aesthetics and philosophy, and chickens and moths — I have to get over to the hardware store and pick up that pair of flame resistant gloves and the welding goggles I ordered — just in case.  😎

Safe and Clear Skies!


7 Responses

  1. Hi John,

    By sheer coincidence I came across Delta Herculis about a week ago, quite by accident. I was testing how well I could see M13 in the twilight with my 80mm F/11 and after finding only a disappointing fuzz, panned southeastward until I came across a yellow white star of the third magnitude.
    I had been using my 18mm BGO yielding 50x. When I centred the star I noticed a tiny spark right up against it. Intrigued, I increased the magnification to 180x and confirrmed that this star indeed had a ‘companion’. I was unsure of what star it was, as the twilight was hindering a clear identification. So, I rushed inside and looked up an atlas to discover that I was looking at Delta Herculis. Curiously, Burnham’s Celestial Handbook stated the stars are unconnected and are actually moving at near right angles to each other!
    The 8th magnitude companion was so close to the yellow white primary that I was sure it was a bona fide companion but recent literature suggests this system is quite complex, as you have so elegantly pointed out!

    With best wishes,


  2. Kaler mentions that the motion of Delta “B” is such that apparently it also isn’t linked gravitationally to the primary. That means the only truly linked pair of stars in this system is Delta Aa, the pair that is only six hundredths of an arcsecond apart — the pair we can’t even begin to see.

    And for me that makes this system all the more remarkable. We’re actually seeing “A” and “B” at an ideal time with regard to separation.

    That really became clear when I was looking at the data in the Washington Double Star Catalog, which reveals quite a bit of movement for “B”. In 1799 it was located 33.8″ away from “A” at a position angle of 163 degrees. The most recent WDS data, from 2009, shows “B” at a distance of 12.4″ with a PA of 286 degrees. That gives it a motion toward the primary of one tenth of an arcsecond per year. So in a hundred years or so, this is going to be a rather difficult one to split. But of course, by then, all back yard telescopes will be equipped with a highly advanced form of adaptive optics. I’ve got my order in already. 😉

    Actually, now that I think about it, if you plot a path from 163 degrees to 286 degrees, it would seem that Delta “B” has gone past its closest point to the primary and is now traveling away from it. Of course, it’s not the only thing that’s moving. We’re moving and Delta “Aa” is moving, too. But I think I’ll leave in the order for the adaptive optics anyway.

    As long as I’m at it, the other WDS data shows Delta “C” was located 358.9″ from the primary at a PA of 352 degrees in 1921 — the 2009 figures show it separated by 173.8″ at a PA of 357 degrees. So it’s moving rather fast as well.

    On the other hand, “D” is barely moving. In 1897 it was 190.7″ arcseconds away from “A” at a PA of 96 degrees — in 2009 it had barely moved to a distance of 191.6″ at a PA of 93 degrees.

    And I love that description of “B” as a spark! It certainly is that!

  3. Fascinating posta nd comments – I just spent an hour with this wonderful collection of stars – I hesitate to call it a “system” because from all you and Neil have said, it’s only a system because of our point of view. But it’s still a lot of fun.

    I like your “nourish your neurons” comment, john. Immediately it reminded me of a discussion I had earlier today on Facebook with a former student in which she suggested some folks are playing 3D Chess while others looking at the same set of facts are really playing checkers. So the trick becomes how do you get your brain to see the 3D chess game – an apt metaphor for a collection of stars such as this – when what it keeps reporting looks more like a checkerboard? 😉

    That said, I think most of my time this evening was spent in checkerboard mode and what struck me was something John remarked on – the similarity to Polaris. I was limited to the 60mm TV and 85mm TV on dual mount and that combined with below average seeing meant I really didn’t see these stars at their best and the biggest challenge to me was the secondary. The significantly fainter “C” and “D” components were easy.

    With the 60mm I could barely glimpse the secondary at 70X. Even with the 85mm it was a challenge, best seen tonight with a 9mm Nagler giving 66X – though I did see it at higher powers as well – but I never had a solid, steady view for more than a second or two. So how’s this compare to Polaris? There’s 5.2 magnitudes of difference between these two stars – with Polaris it’s 6.2 magnitudes – which should make Polaris more difficult. But with Delta we’re dealing with a separation of 12 seconds and with Polaris it’s 18 seconds, which should make Polaris easier. I suspect this adds up to a wash and they are equally challenging to small scopes and require at least average seeing.

    One brief note – what threw me for a moment when I first tried to identify the outer components were two stars in your outer “ring of fire.” They almost mock the “C” and “D” stars – just about the right spacing and the right PAs – and with the 60mm scope, especially, dare you to mistake them for “C” and “D. ” Of course, “C” and “D” are really about one fourth the distance from the primary as these two coyly placed impostors. All it took was a little more dark adaption for my eyes to quite easily pick out the real stars in the inner ring. Hmmm . . . too bad we can’t share this with Johnny Cash – or were you thinking of another “ring of fire” when you put that heading on this post?

    Anyway – delightful find and post – thanks. This was my best observing experience in about two months, given other distractions in my life during this period. Now I’m going to head out to find Vesta – I hope. Boy that little sucker is moving fast. I had a chart printed out from a few nights ago when it turned out too murky with too much moon and it’s already out of date.

  4. Delta (δ) Herc really requires a good night. In fact, to experience the full effect, Dr. John recommends four things:

    1. Four inches or more of aperture.
    2. A dark, moonless night
    3. At least average seeing
    4. At least average transparency

    If you follow this prescription, and read the directions on the bottle, I can almost guarantee some magic.

    I got a taste of it again last night, and again it was with a four inch refractor. I haven’t made up my mind which is the best view — the wide view that places the outer ring about 1/3 of the way from the edge of the field of view, or the tight view which puts the outer ring at the very edge of the field. Now that I think about it, what works well is to alternate between the two views a couple of times to get the full effect. The wide view in some ways is the most pleasing, but you need to spend some time with the closer view to appreciate the subtleties of the expansive view.

    And then of course you can always throw caution and subtlety to the solar wind and crank up the magnification far enough to drive the primary and secondary apart — which is really a very impressive view. With enough space between them, that small spark (thanks, Neil!) of a secondary just seems to float in space at a safe distance from the over-powering glare of the primary.

    I also had a chance to do some comparison between Polaris and Delta (δ) last night using a 50mm Zeiss refractor. And you’re right, Greg, it’s a wash. What I saw seems to be what you saw with the 60mm Televue.

    An 11mm TV Plössl gave me 49x, and at that magnification, the secondary was just barely detectable for brief moments in the case of both Polaris and Delta (δ) Herc. I could pry it out of the glare with a 4mm Astro-Tech Plössl, but the 135x it gave me was about at the limit of the small scope’s light gathering ability. It’s one of those cases where you can say you saw it, but it was not quite the satisfying view I wish it had been.

    So I went back to the four inch scope and allowed myself to be mesmerized by the magic once more.

  5. I’m extremely impressed with your writing skills as well as with the layout on your weblog. Is this a paid theme or did you customize it yourself? Either way keep up the excellent quality writing, it is rare to see a great blog like this one today..

    • Thanks for the compliment — we appreciate it! The layout was designed entirely by Greg.

  6. Delta Herculis — another star that draws me like a moth to a shining lamp light.

    I keep going back to this beautiful and entrancing configuration of stars in hopes of absorbing some very vague, elusive, un-name-able quality that lies just beyond my grasp. Sooner or later I suppose I’ll grab hold of it, and when I do, I may well need the asbestos gloves mentioned in the last lines of the post above.

    Part of the reason I keep going back is a desire to capture that intoxicating and mesmerizing glow radiating from the primary. I think I finally got it with the aid of my five inch f/15 D&G refractor, and added it to the center of the post above (here, also).

    With the aid of that scope’s relatively narrow field and a reasonably low magnification of 106x, I felt like I was hovering over the heart of this collection of stars. It was as close as I’ve come yet to seizing that mysterious essence out of the center. I swear I could taste the photons and smell boiling hydrogen gas — but then again, it might have just been the lingering smell of charred steak still hanging in the air from a neighbor’s late outdoor barbecue. Whatever it was, it sure was appetizing.

    For those who have access to Astronomy Now, if you turn to page forty of the August issue, you’ll find my obsession with Delta Herculis has found its way into the magazine. They did a beautiful job with the layout of the article, and I’m thrilled past the tips of my focus fingers that it was published!


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