• 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.

A Sigh for a Psi (ψ) and a Sigma (Σ) Enigma: 23 Orionis; Psi (ψ) Orionis and Σ712; 33 Orionis and Σ721

When I was roaming and Rho-ing through Orion a week or two ago, I  banged my head rather hard on several double stars in the area north of where I was exploring.  After the swirl of stars around my eyes subsided (and my language improved 😉 ),  I made a mental note to come back and take a look at them.   Which led to the two evenings of observations described here — the first being a challenge to my balance, and the second resulting in some insight into eyepieces — what works, what doesn’t, and why  — that I had been mulling over for several months.   And of course, some out of this world double star observations.

But before you put your coat on to come out and join me, you might want to grab a couple of motion sickness pills.  The stars tonight look like the storm tossed lights of fishing boats on a wild and raging sea.

Fortunately, the first one on our list is separated by a reasonably wide 31.6 arc seconds of sky, so you won’t need to grip the railing too tightly.

The upper two-thirds of Orion is seen here, with our targets located halfway between Bellatrix and Mintaka. Click on this and any of the other images that follow for a larger view. (Stellarium screen shot with labels added).

23 Orionis  (Σ 696)  (H IV 84)            HIP: 25142    SAO: 112697
RA: 5h 22.8m   Dec: +03° 33′
Magnitudes: 5.0, 6.8
Separation:  31.5″
Position Angle: 30°  (WDS 2009)
Distance: 962 Light Years
Spectral Classification: B1

This one is easy enough to find — just draw a line from Mintaka, the westernmost of the three belt stars, to Bellatrix and point your telescope at the center of it.  In an 8×50 correct image finder with a four to five degree field of view, you’ll see an image that should match the chart shown below.  As you can see, all of the stars on our list are within a single field of view.  So for this session you won’t need to go to the  GOTO apparatus 🙂

All five of our stars are located within the circle, which represents the field of view in an 8×50 correct image finder. (Stellarium screen shot with labels added).

23 Orionis will be at the west edge of your field of view.  If you happen to be looking at Orion while it’s on or near the meridian, and are using a correct image finder, that would put it on the right side of the finder, just as you see it in the chart.

23 Orionis – note that the image is inverted to match the eyepiece view in my refractor. (STScI photo)

This is a nice, wide pair as I look at in my 60mm f/15 refractor equipped with a 20mm Plössl (45x).  The 6.8 magnitude companion is just close enough to suffer a bit from the glare of the fifth magnitude primary, so you may have to ogle it closely to see it, but once you pick it out, it’s easy enough to see — although with the horrible seeing tonight, it really takes some effort to hold the image of it steady.  I also have a four inch f/10 refractor out here tonight, and using the same 20mm TV Plössl (which gives me 50x), I can see the primary is a very respectable bluish-white, and the secondary seems to be almost identical in color.  Despite the squirrelly seeing, I put a 14mm Radian (71x) in the four inch scope to get a closer look at the secondary in order to confirm the color — and sure enough, it’s the same blue-white as the primary.  This double is one of those that Haas describes as a “showcase pair” in a 60mm refractor — and I’m sure it’s much better on on a better night than this one.  She sees “azure white and ashy blue” — which I think translates into bluish-white — but is a wording I wish I had thought of, and which really describes them well.

Because of the seeing — which by now is totally off the scale of rotten — I switch to a 24mm Tak (42x) in the four inch refractor, and the view improves considerably.  This really is a pleasing pair — if only they would hold still for half a second!!!

And, as I look now at the separation of the other stars on my list — 1.9″, 2.9″, and 3.0″ — I can see that it’s hopeless to try for them tonight, so I decide to give up and wait until tomorrow evening …………………….

Psi (ψ) Orionis (28 Orionis, or Psi-2)  (Knott 3 — KNT 3 in the WDS)
HIP: 25473    SAO: 112775 
RA: 5h 26.8m   Dec: +03°  06′
Magnitudes: 4.6, 8.6
Separation:  2.9″
Position Angle: 327°  (WDS 1991)
Distance: 1418 Light Years
Spectral Classification: B2

Σ 712  (H I 53)
HIP: 25443    SAO: 112765
RA: 5h 26.5m   Dec: +02° 56′
Magnitudes: 6.7, 8.6
Separation:  3.2″
Position Angle: 66°  (WDS 2007)
Distance: 509 Light Years
Spectral Classification: B9.5

…………………….. And here we are again!  Sure doesn’t take long to spend twenty-four hours around here!

And the seeing looks like it should be much better now because the stars don’t look like fireworks tonight — although I can’t really see much because of the murky haze.  But because Orion is one of the brightest constellations to grace our skies at night, I’m still able to trace its outline.  So what the heck, let’s get a scope set up and see what develops tonight and ignore the fickle forecast.  In consideration of the challenges we have ahead of us, I’m going to go with the AR-5, which is now equipped with a 60mm f/13.3 refractor that I attached to it last week while the rains were raining.

To test the seeing, I decide to take a quick look at Eta (η) Orionis, which has a separation of 1.7″.   I’m able to barely split it through the haze with a 10mm eyepiece (118x) in the AR-5, so it REALLY looks like we might just be able to get something done on these close stars tonight.

A quick look at 23 Orionis in the 60/800 at 40x is a bit better than last night because it isn’t jumping around, although in the haze the secondary is still tough to pick out.  But let’s move a bit to the east of it now and try our luck on Psi (ψ) Orionis and Σ 712.

Psi (ψ) is one of those stars that has more names than it does components.  Its Flamsteed designation provides it with the name 28 Orionis, Sissy Haas’s Double Stars for Small Telescopes refers to it as Psi-2, the Sky and Telescope Pocket Atlas designates it as just plain Psi, and the Cambridge Double Star Atlas calls it by two names, Psi and Knott 3  (G. Knott recorded some double star discoveries and observations in the 1860’s, but that’s about all the information I can find on him).   Overwhelmed by all those names, we’ll just sigh and call it plain old Psi — as in Ψ.

And if you’re curious, on our first chart Psi-1 is the star located to the south of Psi (ψ) which is labeled as 25 Orionis.

In the 60mm scope, both Psi (ψ) and Σ 712 are a wide pair that make a pleasant impression at 40x, even in the haze — which, by the way, is getting thinner (!) — and are even better in the 127mm aperture of the AR-5 at 49x.  What I’m looking for at the moment is Psi “B”, a dim companion at 327 degrees, just a bit west of north — and this is proving to be a tough one.  Eta (η) Orionis, at 1.7″ was easier, because there is only 1.3 magnitudes of difference between the two stars.  But here, even though the separation is greater at 2.9″, we’re dealing with a difference of four full magnitudes.  Which in plain language means the Psi (ψ) secondary is 40 times fainter than the primary, whereas in the case of Eta (η), the secondary is a little less than six times fainter than the primary.  To get that figure, you multiply 2.51 by itself for every full difference in magnitude between the components.  (For Psi, that’s 2.51 x 2.51 x 2.51 x 2.51 = 39.6)

At any rate, I’m not having any luck at all here.  I’ve worked my way up from an 18mm Tak LE (66x) to a 14mm Radian (84x), then a 12.5mm Tak (94x), and now I’m staring into a 10mm Tak LE (118x), and still cannot see the faint photons of that secondarial light.  Hmmm, I look down in the opposite corner of the eyepiece at Σ 712 —- and what in the name of Knott is this?

It’s a clean split.

Astounded, I back away from the scope now and look up at the sky for an answer from on high — and it’s cleared completely!  In fact, it’s absolutely stunning — black sky and gleaming stars everywhere I look.

But back to the scope.

What we have here is a failure to computicate.  By that I mean — first of all — that the 1.9 magnitude difference of the components of Σ 712 translates into “B” being about six times fainter than “A.”  Second — also in it’s favor is the greater separation of the two stars — 3.2″ here, versus 2.9″ for Psi (ψ) — a difference which really is more slight than significant.  And yes, as we’ve just seen, those two factors actually should make Σ 712 easier to split than Psi — BUT —  because the primary of Σ 712 is 2.1 magnitudes fainter than Psi (ψ) primary, I really had expected that it would be more difficult to split — as in less light, less luck.  So this Sigma is an enigma for sure — or maybe we’ve just learned something we can park in the memory banks for later use.

HOWEVER —  having succeeded so admirably with the photon friendly Σ 712, we now have a clue of what to look for as we heave a huge capital sigh (Ψ) of thanks and return to Psi (ψ).  Why?  Because the secondaries of both stars are the same magnitude — 8.6!  Aha!  A fortuituous unforseen stroke of photonic fortune!

So, glancing at the 8.6 magnitudes worth of photons glimmering from Σ 712’s secondary, I look very closely again at Psi (ψ) for a similar soft point of light  — and nothing.  Maybe the 10mm is causing too much glare, so I put the 12.5mm back in, and still there is nothing where that speck of light should be.  So I reverse directions and reach for a 7.5mm Tak (157x) and take another look — lots of glare, a slightly unsteady image, and no sign of Psi “B”.

OK.  There’s only one thing to do.  I go into the house and, from it’s hallowed location on a hall shelf, I remove the mysterious orange inscribed 7.5mm Celestron Plössl that has saved me from failure so many times in the past, and holding it with great care in the outstretched palms of my hands I return to the telescope and make the sacred switch.  As I slowly bring the image into focus, I notice there is virtually no scattering of light from the primary and that the image is more stable.  Already the magic is working, and I’m not quite focused yet!

A bit more, a bit more, just one more bit, and then another microscopic turn of the fine focus knob — THERE IT IS!

I got it, I got it, I got it,   I     GOT      IT!

Got what, you ask?  A very, very, very fine point of light — see it?  Not much more than a speck, really, but look!   It’s really there!

More magnification, you say?  Well, why not!

I put a 5mm Tak LE  (236x) into the diagonal, and again I get so much scatter from the primary that I can’t see past it to the secondary.  Well, it just happens that the mysterious 7.5mm Plössl has a mate that I haven’t been too impressed with yet, but I decide to give it a try.  Back in the house, open the box, and remove a 6.3mm Celestron Plössl (187x) of the same vintage and heritage as the 7.5mm.  Into the diagonal it goes, a few turns of the coarse focus knob, a few more turns of the fine focus knob — and slowly a sharp image begins to come into view — and LOOK! — it’s both stars again!

And it’s pretty darn steady, too.

I’m frozen into position —- shoulders hunched down, head bent forward over the eyepiece, right hand perched just beside the fine focus knob.  I have no desire to move from this spot for a couple of hundred years.  This is A-MAZING! One well-rounded, sharply defined yellowish white globe of light shadowed by a very miniscule, very fine, very faint point of light right at the top of it — that is as sharp and clear as it is faint.

Whew!  Get a grip, man!  You’ve been at this for an hour and half.  We still have another pair of stars to look at.

33 Orionis  (Σ 729)  (H I 22)         HIP: 25861    SAO: 112861   
RA: 5h 31.2m   Dec: +03° 18′
Magnitudes: 5.7, 6.7
Separation:  1.9″
Position Angle: 28°  (WDS 2011)
Distance: 1568 Light Years
Spectral Classification: B1.5

Σ 721  (H IV 45)        HIP: Not assigned in Simbad    SAO: 112824
RA: 5h 29.6m   Dec: +03° 09′
Magnitudes: 7.1, 9.1
Separation:  25.7″
Position Angle: 149°  (WDS 2010)
Distance: ?????
Spectral Classification: B5

Well, there’s no encore for something like that experience, so reluctantly we move on.

If you look at the second chart above, you can see that our next pair is on the east side of our finder field, and slightly north.  We’re not moving far, fortunately, so if these prove to be a disappointment, we’re going to go right back to the mesmerizing Psi (ψ).

You’ll notice if you position 33 Orionis in the northeast corner of your eyepiece, Σ 721 will be positioned on the opposite side of the field and a bit south.  Hmmm — this view is remarkably similar to that of Psi (ψ) and Σ 712.  Uh oh, here comes that deja vu feeling all over again  ……………..

But actually, with a 14mm Radian (84x) in the AR-5, 33 Orionis is a bit elongated, and I can see the split in Σ 721 with no problem.  I replace the Radian with a 12.5mm Tak (94x) and the elongation becomes a stretched out pair of stars that won’t quite come apart, so I remove the 12.5mm from the focuser and replace it with a 10mm Tak (118x), change the focus slightly, and —–

5 …… 4 ……… 3 ……….. 2 …………… 1 ………………………..    we have lift off!

Wow, that was a whole lot less struggle — and look at that view!  The primary is mainly white with a trace of blue, and hugging it closely — with a slice of black sky in between — the secondary is about half again as small and a little bit less white with a slight touch of yellow.  Both are very sharp and very vivid.

On the other side of the field, the primary of Σ 721 is pretty close to the color of 33 “B”, and I notice just the faintest tinge of red in the 9.1 magnitude secondary.  Now normally I wouldn’t expect to see any color at all at that magnitude, but I look several times, and with several different magnifications, and it’s still there.  You have to look closely at the sketch to see it, which approximates pretty well the way it appears in the eyepiece.

And just as I’m adding the last star to my sketch, I notice the field is getting dim.  I look up, and the entire western half of the sky is engulfed in fast moving clouds.  Usually, when there’s a sudden change like this, I can detect it in the eyepiece because the seeing begins to deteriorate quite quickly.  But not this time — it literally goes from clear to solid clouds in not much more than sixty seconds.  It really looks like someone has thrown a blanket over the entire sky, and it feels like it, too, as a damp west wind blows in at the same time.

So, don’t sit here and gawk — it’s liable to be raining in another few minutes!

A Word About Eyepieces

Eyepieces are like star colors — not everyone sees the same thing, and what you see on one night you may not see at all on another night.  Many are the things that affect the view through an eyepiece  — like aperture, focal length, baffling — not to mention seeing, transparency, moisture in the air, and what you had for dinner.

The Celestron 7.5mm has really done some marvelous things for me when I’ve had it in a focuser.   But, when I first got it, I was absolutely not impressed with it.  It went back in a box and stayed there for well over a year.  Similarly, the 6.3mm Plössl of that same line did not impress me at all when I got it about a month ago.  It wasn’t until I tried it on Psi (ψ) Orionis that I had any success with it.

The Tak LE’s are excellent eyepieces.  There is no question that their light transmission exceeds that of the two Celestron Plössls. But they do scatter a bit of light, and when there’s moisture in the air, or as in the case described above, I’m trying to split a close pair of stars separated by a wide range of magnitudes, they may not be the best choice.  Still, that’s not an absolute rule.  Tomorrow night they may work just great.

And the same applies to the Radians — superior light transmission and great contrast, but also a bit of scatter at times. And similarly, what works well tonight may not work at all tomorrow night.  Or, to put another spin on it, what fails tonight may succeed beyond your wildest dreams the following night.

So don’t interpret any of my comments on eyepieces as the definitive description of their peformance.  They aren’t.

What I try to do to deal with the issue is have a couple of different kinds of eyepieces of each focal length for the higher magnifications, since that’s where problems like those described above begin to show themselves.  In addition to the Taks and Radians, I try to blend in a few Plössls and Orthos because they have fewer elements of glass and because their fields of view are a bit more narrow.  For some reason — and I have no real idea why — the Plössls and Orthos aren’t affected quite as much by seeing.  Many times — and I’ve described it above and several times elsewhere — the image is more stable in the narrower fields.  But not always.  And if the seeing is really rotten, nothing makes any difference.

So take all of this as a reflection of my experience.  Yours could very well be different.

And if anyone quotes me, I’ll deny everything.  🙂


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: