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Epsilon (ε) Geminorum: “A Star with a Distant Companion, on Castor’s Right Knee”

Careful now, careful!  Get it centered, you don’t have much time ………  got it!   Now, look in the eyepiece and get it focused quickly, easy there — HURRY, the clouds are almost here   …………….    THERE IT IS!   Oh, wow, there’s that luscious yellow again, and the scatter of stardust surrounding it on that black velvet background  —-   WOW!!!!   …………..    Hold it.   Hang on to your wow  ……….     LOOK!    It’s fading already  ……………….    it’s gone!   IT’S GONE!      Arghhhhhhhhhhh!!!!!!

Real-life drama here on the rain infested, wind blown, hail strewn, snow socked northwest coast of Oregon.   The day before — and I exaggerate not one iota — there were 60 mph winds in the morning, followed by 2.25 inches of rain in the afternoon, followed by three inches of snow in the evening — and people actually think of this as a vacation destination?

So when I saw huge holes in the clouds the following evening, I couldn’t resist — even though I knew the Sky Gods were just itching to lure me into sucker hole hopping again.  Which they did.  And you just read what happened.

But that was only the first half of it.  The second half came after I went in the house to put on a warmer coat and came back out, only to find the heavens were throwing hail at the ground.   Arghhhhhhhhhhh!!!!!!  again.  Why do I do this?

There’s no quick answer to that question, but in this case the cause was definitely the beautiful deep yellow of Epsilon (ε) Geminorum.  My first addicting glimpse of its glamorous yellow was back in late December after reading Sissy Haas’s description of it:

60mm, 25x: Beautiful pair at low power!  It’s a brilliant Sun-yellow star with a tiny speck of light next to it.  They’re super-wide apart but look like a couple.”

Double Stars for Small Telescopes, p. 77

That did it for me.  I had to look, and I did, and I was very impressed — so I made great plans for this beautiful yellow-saturated primary and its glistening secondary.  But the weather had other ideas, so in the meantime I was left with a craving that increased exponentially with every cloud-covered night.

To tide myself over, I locked up a mental image of that luscious yellow primary in a photon reinforced memory bank, and hoped it could resist the persistent attempts of wind and rain to gnaw through the membrane walls.  They were within a few arcseconds of succeeding when I surrendered to the sinister evils of sucker hole hopping once more.  I know, I know, it was destined to be futile.  But I couldn’t help myself — I had to have a second look.  I had to see it again.  I was starved.  I was helpless.  I was desperate.  My resistance was no longer resistant.

And despite the frustration that resulted, I would to it again in a micro-second of a second.

Epsilon (ε) Geminorum    (Mebsuta)  (S 533)  (H VI 73)    HIP: 32246   SAO: 78682
RA: 06h 43.9m   Dec: +25° 08′
Magnitudes:  3.1, 9.6
Separation:   110.6″
Position Angle:  95°  (WDS 2002)
Distance: 903 Light Years
Stellar Classification: G8

In her description of Epsilon (ε), Sissy Haas also referred to an observation by Admiral William H. Smyth, so I went to my trusty copy of The Bedford Catalog to see what he had to say:

A star with a distant companion, on Castor’s right knee; it is [at] about 26°, or rather more than one-third of the distance, from Procyon towards Capella, where a line led from Rigel through Betelgeuze also reaches it.  “A” 3, brilliant white; “B” 9 ½ , cerulean blue.  This wide object is 73 H. VI; registered by Sir William in 1782, with a distance of 110″.48, but no angle of position given.  It was first measured by S.:  Pos. 93° 42′   Dist. 111″.57    Ep. 1825.04.

This star is called Mebsuta, from al-adhirá al mebsútah, the out-stretched arm; i.e. Castor and Pollux, the bright stars of whose heads form the VIIth Lunar Mansion.”

The Bedford Catalog, Willman-Bell: 1986, p. 157

There’s a wealth of references and information in that quote, so it’s worth going through it carefully and picking it out to learn more about the focus of my irrational obsession.  Let’s start with the Admiral’s directions to it.

Now Epsilon (ε) is really not at all hard to find, and the way I did it (which I thought was the most obvious) was to start at Alpha (α) Geminorum, better known as Castor, and proceed southwest to the next star in the stick figure that forms that side of the constellation, which is Tau (τ).  From there continue southwest along the stick figure schematic for about twice the distance separating Castor and Tau (τ), and you’re there.

Follow along on this chart with the Admiral and I, and one of us will get you to where you need to go! (Stellarium screen image with labels added, click to enlarge).

But the Admiral had a more cosmic outlook when he formulated his directions, managing to cast Epsilon (ε) in the context of a wide swath of the sky.  And there’s an elegant simplicity about each of his approaches which mine lacks entirely.

First:  “. . . it is . . . rather more than one-third of the distance, from Procyon towards Capella . . .”  — and it is!

And second:  “. . . a line led from Rigel through Betelgeuze also reaches it.” — and it does.  And actually, I prefer this one over the others.  By the way, that spelling of Betelgeuse is the Admiral’s, and I’m not about to alter it.    Never argue with the navigator when he’s at the helm of the ship.

We’ll skip past the color for just a second and go onto the next part of his statement  — “This wide object is 73 H. VI; registered by Sir William in 1782 . . .”  —  which is a reference to William Herschel, who cataloged Epsilon (ε) as a double on February 2nd, 1782, and the Admiral’s “73 H. VI” is Sir William’s catalog number.   In the intervening two hundred plus years since his discovery, the order of those characters has been changed to H VI 73, the Roman Numeral “VI” being Herschel’s designation for separations of one to two arcminutes — and this one barely makes the cut.

And then the Admiral adds cryptically, “It was first measured by S.:  Pos. 93° 42′   Dist. 111″.57    Ep. 1825.04.”  That is a reference to Sir James South, who observed Epsilon (ε) on two occasions — December 29th, 1824, and February 6th, 1825 — and numbered it as DXXXIII (533) in his catalog.  If you look at Sir James’ separation and position angle measurements and compare them to the current WDS numbers, you’ll see the secondary’s position has barely changed in the 187 years since his last measurement.  Which is rather surprising, since the secondary is considered to be unrelated gravitationally to the primary.  Kaler mentions that the secondary is thought to be the same distance away as the primary — and if that’s the case, the two stars are essentially traveling in tandem through the galaxy.

Now let’s return to the color.  Admiral Smyth describes the primary as white, as did William Herschel, who ignored the secondary’s color.  South described the secondary as blue and ignored the primary’s color.  But — at least we have agreement between the Admiral, South, and Haas on the secondary.  So why no consensus on the primary?

I saw a very rich yellow, Haas saw “Sun yellow,” and its spectral classification of G8 (see this chart) means it’s firmly in the yellow camp and inching tentatively towards orange.  If it was classified as G2, as the Sun is, it would be tending toward white.  Jim Kaler describes the primary as being in a “rather advanced state of aging” and puts its surface temperature at 4360 Kelvin, which is considerably cooler than our sun’s 5777 Kelvin — another reason for Epsilon (ε) to favor yellow over white.

Delicious, luscious, glamorous, gleaming, and uniquely saturated in yellow, with a hint of cerulean blue in the secondary. East and west reversed to match the refractor view. Turn out the lights and click on the image to be suitably hypnotized by the Mebsutian magic.

So even though everything points solidly toward yellow, the truth is that star colors often defy such rational stellar logic.  It may even be that in this case the larger apertures in use by Herschel (twelve inch f/20 reflector) and the Admiral (long six inch refractor, focal length unknown) had a bearing on the color.  I’ll leave it there, except to say that a 60mm refractor is the ideal instrument for this star because it doesn’t overwhelm it with aperture ……  and that I really, really, really  liked the yellow I saw!

And then there’s that mysterious comment by the Admiral about the VIIth Lunar Mansion  …….  what the heck is that????   I was thrown a bit out of focus by that one, but it turns out it’s a reference to an Arab and Chinese custom of dividing the passage of the moon through the sky into twenty eight sections, or Mansions — and most of Gemini resides in the seventh Mansion.  And what that really  means is this:   while Castor and Pollux reside in luxurious celestial comfort as they wheel their way through the sky, my chattering teeth and I sit beneath them peering through a telescope as moisture runs off the bill of my Star Splitting hat and freezes on contact with the ground.

Finally, there’s that unique name, Mebsuta.  According to a couple of different sources (Kaler and Allen {scroll down to p. 235}), the correct translation of al-adhirá al mebsútah is the “outstretched paw,” which belongs to an early Arabic lion, since at one time, both Zeta (ζ) and Epsilon (ε) represented the two paws of a lion.  Zeta (ζ) is also known as Mekbuda, which refers to the “folded paw” of the lion.  The Admiral has Mebsuta as the “outstretched arm” of Castor, which at least has the merit of fitting it into the current configuration of the constellation.   But regardless of which interpretation is correct, I’ll always think of the “outstretched” limb as reaching for the cerulean blue of the 9.6 magnitude secondary.

And in tribute to the raging weather of Oregon’s north coast (which only differs from the anything but peaceful north Pacific in that it lacks thirty foot waves), I’ll end with this translation of Homer’s Hymn to Castor and Pollux as translated by Shelley. Homer portrays the appearance of the Gemini twins here as a sign to Greek sailors of the coming of spring and calmer seas.

Here’s hoping this will break the weather curse.  😉


Ye wild-eyed muses! sing the Twins of Jove,

.    .    .    .    .     mild Pollux, void of blame,
And steed-subduing Castor, heirs of fame.
These are the Powers who earth-born mortals save
And ships, whose flight is swift along the wave,
When wintry tempests o’er the savage sea
Are raging, and the sailors tremblingly
Call on the Twins of Jove with prayer and vow,
Gathered in fear upon the lofty prow,
And sacrifice with snow-white lambs, the wind
And the huge billow bursting close behind,
Even then beneath the weltering waters bear
The staggering ship — they suddenly appear,
On yellow wings rushing athwart the sky,
And lull the blasts in mute tranquility,
And strew the waves on the white ocean’s bed,
Fair omen of the voyage; from toil and dread,
The sailors rest rejoicing in the sight,
And plough the quiet sea in safe delight.

(From Allen, p, 228)

Clear Skies?  😎

The “Silver Streak,” the hail-repelling Carton lensed 60mm f/16.7 refractor that had the honor of sucker hole hopping with me beneath scurrilous skies. (Click for a closer look)


6 Responses

  1. Terrific description John. Epsilon Geminorum is one of my favorite doubles due to the color, physical size and magnitude differences. After reading this posting I went back through my notes and checked what I had written down regrading color. With my C6R and 13MM Nagler I also described the primary as having a grapefruit color and the secondary as blue. That lines right up with your description.

    I often wonder how much influence the C6R has on the color of stars. If I have a chance I’ll compare Epsilon Geminorum with the C6R and 8″ SCT and compare my notes.

  2. Just want to let you know how much I enjoy reading your blog. I observe from the Denver area with my 78mm refractor and can sympathize with your site problems. I have a street light in my front yard! Needless to say I have more luck with doubles than with Messier objects.

  3. Thanks for the kind comments, John.

    I don’t have a street light to deal with, fortunately, but there is a bathroom light at the same height as my second level observing deck that drives me crazy. I came up with a light screen to block the direct light, but there’s still a glow directly above it that is a real problem to look through.

    • Got a chance to observe epsilon Gem tonight with my 78 mm refractor. Saw a tight pair, yellow and blue. Was best in my 9mm(70x) and 5mm (126x) Naglers but after I had confirmed the double I was able to split it in my 24mm (26x) Panoptic. Colors don’t mean much in my light polluted sky. Wasat, delta Gem, was actually a prettier double to my taste but it was a thrill to split the tighter epsilon pair.

      • Scratch the above comments. I went and re-observed epsilon gem after noting some inconsistencies in separations. It looks like what I thought was a blue secondary was actually a spurious eyepiece reflection. I seen these before, the reflections are almost always yellow and blue in my scope and don’t seem to be related to cool down time as they are generated by the eyepiece. They look exactly like actual doubles but beware if you can’t get a stable position angle estimate because the blue secondary is running circles around your primary!

  4. I am also sucker hole hoppy tonight here in south jersey,but i did have enough time to look at epsilon geminorum , i see a yellow star with a blueish companion through my 80 mm f10 refractor,i have compared star colors between my refractors and my reflectors and don’t see much diffference when the aperatures are the same. Well hope your skies clear up soon John

    thanks for your interesting posts!!!

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