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Pi (π) in the Sky! — Pi-1 Orionis; P-3 Orionis and H VI 83; and OΣ 100, Σ627, and Σ630

What do Orion and a hungry Star Splitter both have in common?  Pi (π!) and Pie!

Now what I have in mind is not quite the same thing as that hungry hunter in the sky — in fact, I would settle for a single slice of it right now, but Orion seems to have six varieties of Pi (π).  They can be found in the western arc of stars which forms his shield.  The two stars at the top (north end) of the shield are 11 Orionis and O2  Orionis.  South of those two stars, you’ll find the Pi’s are lined up in order, north to south, starting with Pi-1 (π-1), and that they belong to five different stellar classifications.  In order, from Pi-1 (π-1)through Pi-6 (π-6), they are A0, A1, F6, B2, B2, and K2.  But I only have one variety in the house — cold and old.

Orion shown here holding a stack of six Pi’s (π’s!). (Stellarium screen image with labels added. Click on the chart for a larger view).

But let’s quit making ourselves hungry here and get busy.  If we’re going to have a late night feast, we need to work up a real appetite.  There’s a real gem of a dual double star waiting out there for us.

First, though, a minor housekeeping measure.  That shield really puzzles me.  It looks more like a bow, as in bow and arrow.   And look at it!  It’s stretched out across fourteen degrees of sky in north to south declination!  If that was you up there holding up all that weight (shields aren’t light, you know) at the end of your outstretched arm, wouldn’t you think your arm would give out after several hundred thousand years of that torture?  It hurts to think about it.

But let’s quit questioning and start hopping.  Forward to the stars, Star Hoppers!

We’ll begin at Bellatrix, located at the northwest corner of Orion.  This would be Orion’s western shoulder if you were staring at him as he was perched on the meridian staring back at you.  And the arm attached to that shoulder is the one that’s holding that  ….  shield that looks like a bow.

Use this chart to locate our first four stars — OΣ 100, Pi-1 (π-1), Pi-3 (π-3), and H VI 83. And don’t forget to click on the chart for a larger view. (Stellarium screen image with labels added)

If you draw a line from Bellatrix northwest to Pi-1 (π-1), you’ll pass through 14 Orionis at the halfway point.  I like to think of this line as the arrow that is perched in Orion’s bow.  (You can see why a shield just doesn’t work here!).  We’re going to imitate a tight-rope walker and edge out along that line now, so stare straight ahead and don’t look down — there’s nothing below you but dark nothingness.

Whew!  Let’s stop at 14 Orionis and get our breath for a second — and by virtue of some cosmic coincidence, there just happens to be a double star here!

OΣ 100             HIP: 24031    SAO: 112481
RA: 5h 10.0m   Dec: +08° 10′
Magnitudes: 7.0, 10.4
Separation:  3.5″
Position Angle: 275°  (WDS 2011)
Distance: 275 Light Years
Stellar Classification: F7

Inverted image to match refractor view of field the field surrounding OΣ 100. (Stellarium image with labels added, click on the image for a larger view)

This tough little devil is located just to the southeast of 14 Orionis.  Looking into a 24mm Tak LE (49x) parked in the diagonal of my AR-5 on Feburary 19th, OΣ 100 formed a triangle with 14 Orionis and the star to the south of it, 6.7 magnitude HIP 23896.  The primary is a pleasing orangish red, and the secondary — well, let’s just say you’ll be doing good to see it, period.  I think I got a glimpse of it in the AR-5 using a 15mm TV Plossl (79x) and a 12.5mm Tak LE (94x). I tried again on a rather nippy twenty-five degree February 25th with a Celestron 102mm refractor, and again, I thought I got a glimpse of it, but I won’t swear to it.

Finally, on March 7th, I cracked it with the AR-5 under slightly better seeing conditions than previous attempts.  I thought I had a glimpse of it with a 12mm Brandon (98x), but a 10mm Radian (118x) did the trick.  I was able to pry it a bit further apart with an 8mm Radian (148x) — at least when it would hold still.  And when it did, there was a very gaping gap between the two stars, and the tenth magnitude secondary was a very visible point of delicate light.

This one reminds me of its nearby relative, OΣ 111, just north of Meissa.  There are 3.2 magnitudes of difference in that one (5.6 and 9.8) separated by 2.9″ — and after numerous tries, it also leaped into sight one night in my 102mm Celestron.  Common sense says both of these should be a bit easier, but if we had any common sense, we wouldn’t be tight-rope walking along this thin thing above nothing.

So let’s leap off of this line dangling in darkness and land at Pi-1 (π-1).

Pi-1 (π-1)   (ENG 19)          HIP: 22845    SAO: 94201
RA: 04h 54.9m   Dec: +10° 09′
Magnitudes: 4.7, 8.95
Separation:  172″
Position Angle:  253°  (WDS 2010)
Distance:  120.6 Light Years
Stellar Classification:  A0

And when we come down, we find ourselves looking at a bluish-white primary.

Pi-1 (π-1) Orionis — note west is at the left to match the refractor view. (STScI photo, click to enlarge)

For the secondary, you better have a score card with the position angle on it or you’ll be roundly confused  — like me.  I remembered this was a wide pair, but I had neglected to look up the PA in the Washington Double Star Catalog (you won’t find this one in the Haas book).  As you can see in the photo, there is a star to the north that is a possible candidate, as well as a pair of fainter stars to the southeast.  Those two blurred into one star when I was looking at them, possibly because of the haze, or perhaps because the sky gods were playing tricks on my eyes in return for calling Orion’s shield a bow.  At any rate, the one you want is lingering over there to the southwest, and is not difficult to see — and I wouldn’t begin to hazard a guess as to color because it was just too faint.  But it was easy to see in a 60mm f/13.3 using a 20mm TV Plossl (40x).

Before we leave, it’s worth a two degree move to the west to take a quick look at an attractive open cluster, NGC 1662, which was easy to see in the 60mm f/13.3 — in fact I first noticed it in my 8×50 finder.  In the AR-5, with the 18mm Radian (66x), I counted about twenty sparkling stars silhoutetted against the black sky.  Rather nice.

Shall we move on now?  The next stop is a real gem — actually, a pair of gems — Pi number three and it’s very close neighbor, H VI 83.

Pi-3 (π-3)   (OΣ 560)  (Tabit)        HIP: 22449    SAO: 112106
RA: 04h 49.8m   Dec: +06° 58′
Magnitudes: 3.2, 8.8  (11.3 – WDS 2010)
Separation:  75″
Position Angle: 168°  (WDS 2010)
Distance: 26.2 Light Years
Stellar Classification: F6
Status: Optical pair

H VI 83                 HIP: 22490    SAO: 112117
RA:  04h 50.3m   Dec: +06° 57′
Magnitudes: 7.2, 8.7  (10.14 – WDS 2002)
Separation:  94.8″
Position Angle:  5°  (WDS 2002)
Distance:  591 Light Years
Stellar Classification: A2

Now you can call Pi-3 (π-3) by that name, or by 1-Orionis, or by STT 560, or by Tabit — it answers to all four names.  But H VI 83 is just H VI 83, and with a name like that, it doesn’t need anything else — although it has been called something else, which we’ll get to in a moment.

And to what does a name like H VI 83 refer, you ask?  William Herschel came up with this one.  He set up six classifications for his double star observations, basing them on the separation between the stars.  The classifications are Roman Numerals “I” through “VI”.  Category “VI” is the widest, for stars between 1′ and 2′ (or 60″ and 120″) in separation.

Now delving into the explanation of the name of this star caused me more than a few problems because the Cambridge Double Star Atlas identifies it as H V 83 on both its chart of Orion and in the back of the atlas where the data is listed — and Herschel’s category “V” is for stars with separations of between 30″ and 1″  — which doesn’t fit this one at all.  On the other hand, the Washington Double Star Catalog labels this one as “H 6 83.”  I was able to track down the original list of 500 hundred stars classified by Herschel, and found it’s listed there as H VI 83, not H V 83.  (The stars in that list are in order of right ascension, which is at the extreme right).   So it appears the Cambridge Double Star Atlas has it wrong and the WDS has it right.  For an excellent source of information on William Herschel and his double star endeavors, take a look at this site.

But it’s what’s in the eyepiece that counts!  So let’s quit quibbling and take a peek.

H VI 83 is the pair of stars on the right side of this sketch. (Click on image to enlarge.)

Ah, stellar bliss.  Especially after the interesting, but somewhat less than spectacular two stars we’ve already hopped past.

If you’re using an eyepiece with any kind of a decent field of view, you’ll see both of these in the same field.  I was using a Meade AR-5 with an 18mm Radian (66x) that gave me a field of view of about nine-tenths of a degree and scooped both of them out of the sky with no problem.   I could also see both of them in the more narrow field (.45 of a degree) of a 12mm Brandon at 98x, which was a terrific sight. The primary of Pi-3 (π-3) is a very noticeable yellow, and that of H VI 83 is bluish-white.

In my 60mm f/13.3, Pi-3’s secondary was very difficult to see in the 3.2 magnitude glare of the primary, but the H VI 83 secondary was a breeze, thanks to a much dimmer primary magnitude of 7.2.  Here again, though, there are discrepancies.  The WDS lists the secondary magnitudes at 11.3 (Pi-3) and 10.14 (H VI 83).  The Cambridge Double Star Atlas, on the other hand, has them at 8.8 and 8.7.  I wasn’t aware of the discrepancies at the time I looked at these two stars, but I would be very surprised if Pi-3’s secondary could be seen at all in the glare of the primary if it actually has a magnitude of 11.3.  That would make the secondary 1575 times fainter than the primary.  And I had no problem seeing the H VI 83 secondary in the 60mm scope, so that argues against it being a challenging magnitude of 10.14.   So I’ll lean toward the Cambridge Double Star Atlas on this one.

And now, let’s slide right on down in a gentle arc to the bottom of the bow — or shield.

Use this chart to locate Σ630 and Σ627, click to enlarge. (Stellarium screen image with labels added)

Σ 630  (A-BC is H III 52)            HIP: 23419    SAO: 112340
RA: 5h 02.0m   Dec: +01° 37′
Magnitudes   A-BC: 6.5, 7.7     A-D: 6.5, 10.4
Separation    A-BC: 14.4″         A-D:  131″
Position Angle   A-BC: 49°  (WDS 2011)        A-D:  101°  (WDS 2002)
Distance:  508 Light Years
Spectral Classification: B8, B8

First we’ll move south to Pi-4 (π-4), then past the visual pair of Pi-5 (π-5) and 5 Orionis, on to Pi-6 (π-6), and come out practically at Σ630, a tempting little triple star.  Geez, all this Pi (π!) is getting rather tempting.

Click on image to enlarge.

The primary of this one is an eye-catching blue-white, and the slightly dimmer secondary appears to me to have a slight tinge of yellow or red.  Haas notes the secondary was seen as blue by Castle and Webb, but I missed that  — could have been because it was low in the sky by the time I got to it.  The third star, “D,” floats out there colorlessly all by itself.  If you look closely at the field surrounding these three stars, you’ll see they’re nested in a north-south oriented trapezium, which is also pointed out by Haas.

If you have excellent seeing and a lot of aperture (fifteen inches?) and observe at about 6000 ft of elevation, you might have a shot at splitting the secondary, “BC.”  The magnitudes are 7.8 and 10.5 with a separation of four-tenths of an arc second, as in .4″  —  I’ll pass on this one.

Last stop: Σ 627!

Σ 627           HIP: 23287    SAO: 112305
RA: 5h 00.6m   Dec: +03° 37′
Magnitudes: 6.6, 7.0
Separation:  21.2″
Position Angle: 260°  (WDS 2011)
Distance:  140 Light Years
Spectral Classification:  B9, B9

If you look at the last chart above, you’ll see that Σ 627 is at the point of a triangle which it forms with Pi-6 (π-6) and Pi-5 (π-5), both of which make up the base.  In fact, it’s exactly two degrees north of Σ 630 and only one minute further west in right ascension.  Put those setting circles to work here!

Σ 627 — the secondary is the left one of the two stars. Note west is at the left to match the image in a refractor. (STScI photo, click to enlarge)

The first time I saw these, I barely got a glimpse of them before they disappeared behind a stand of trees to the southwest of my observing sight.  What I noticed immediately, though, was two bluish-white dots of almost identical brightness.  I caught them on another night in my 102mm Celestron refractor with an 18mm Ortho (56x), and darned if they weren’t still white!  Actually, my first thought when I looked at them was how similar in appearance they were to Beta Monocerotis when you can only detect two of its three stars.  At any rate, they stand out well from the background stars.  You can’t miss them.

So another star hopping tour comes to a successful stop.  And after sampling all of this Orionic Pi (π!), I think it’s time for the real thing.  With a cup of steaming hot tea to warm up our toes and our nose.

And I’ll leave it to you to decide whether the arc to the west of Orion is a shield or a bow.  You know what I think.  Of course, there is one slight problem.  There’s that other arm up there holding the club.

All I can add is that Jim Kaler calls the shield a  …….  “cloak.” 😉


One Response

  1. Terrific tour, John, but you got so focused on your stomach you must have missed the fact that you’re publishing this just two days before Pi Day!


    Yeah 3.14.11 – well, the last “1” doesn’t work so well, but March 14, to the math inclined around the world is Pi Day.

    Now that said, I like your Pi in the sky and it’s better for me than what’s on the table. I especially like that last pair – Σ627. If the weather holds, I’ll take a look tonight.

    Cloak? Well, sort of.. . I’ve always thought of it as a shield, but of a primitive sort, a huge bear or lion’s skin, loosely draped over his arm. And that would be darned heavy as well, but it would tend to shield you.

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