• 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.

The Other Alula: Alula Borealis (Nu {ν} Ursae Majoris)

I came across this one two weeks ago when I was in search of the ethereal yellow light of Alula Australis, also known as Xi (ξ) Ursae Majoris.  It can be found shining about 1.5 degrees north of Xi (ξ).  I would gladly have spent some time with it that night, but between being totally immersed in splitting Xi (ξ), and having the night cut short by clouds, I never had the chance.  But — I had gotten a glimpse of it in my finder — and the contrast of its reddish orange glow with the deep yellow of Xi (ξ) was etched firmly into my photonic Star Splitter memory screen.  So like a hummingbird being pulled north in the springtime by a vague primal urge, I knew I had to return to see what secrets I could see behind its beckoning glow in the northern sky.

And when I did, like a hummingbird, I found myself flying in reverse.

However — I had no choice but to wait impatiently for two weeks while clouds and rain and hail and thunder were followed by more clouds and more rain and more hail and more thunder — and there was still more after that.  After this long wet winter, I’m beginning to appreciate why Lewis and Clark were less than thrilled with the north coast of Oregon:

Again we had a wet stormy day, … There is more wet weather on this coast, then I ever knew in any other place; during the month we have had but 3 fair days; and there is no prospect of a change.  (December 5th, 1805)

The winds violent Trees falling in every derection, whorl winds, with gusts of rain Hail & Thunder, this kind of weather lasted all day, Certainly one of the worst days that ever was!  (December 16th, 1805)      Lewis & Clark Journals

Finally — the eventual night of clearing came, but along with it was a warning from the Clear Sky Chart:  seeing was forecast as dark gray squares.  Translated, that means very poor seeing, as in one on a scale of five.  And believe me, it lived up to it — it might have even been worse than that.

I wanted to get a good look at Porrima, though, because I was interested in comparing it with Xi (ξ), since the pairs of stars in each are similar in brightness and separation.  Somehow, I must have found the only relatively decent location of seeing in the entire sky, because I was able to get a clean split of Porrima at 167x.  Thrilled with that, I moved up to Xi (ξ) — which was directly overhead — expecting to do the same.

And right away I found there was zero chance of splitting the gyrating glow of that yellow star — it wouldn’t hold still for a fraction of a second — but that didn’t prevent me from trying.  I refused to give up until both eyes were crossed and I was so dizzy I couldn’t stand up and my dinner was performing jumping jacks in my stomach.  I’m still not quite sure how the seeing could have been so decent over in the southeast part of the sky at about forty-five degrees above the horizon and sixty seconds later be totally atrocious right at the zenith.  I think the Sky Gods are still mad because I convinced them the over-sized military surplus erfle I sacrificed to them was an Ethos.  Probably better not try that one again. 😉

Anyway, since I was nearby, I moved the scope a degree and a half north and took a look at the other Alula.

The two Alulas in relation to Ursa Major and Leo. Alula Borealis is the northern one (Borealis means northern), Alulal Australis is the southern one (and Australis means southern). Stellarium screen image with labels added – click on the chart for a larger view.

Alula Borealis  [Nu (ν) Ursae Majoris(Σ 1524)     HIP: 55219    SAO: 62486
RA: 11h 18.5m   Dec: +33° 06′
Magnitudes: 3.5, 10.1
Separation:  7.4″
Position Angle: 149°     (WDS 2005)
Distance: 421 Light Years
Spectral Classification: K3

Now follow this one closely.  As I mentioned above, we’re going to approach in reverse.

When I moved my 105mm f16.7 refractor north to Nu (ν), sitting in the diagonal was the 9mm Nagler (167x) I had been fruitlessly fidgeting with in hopes of coaxing Xi (ξ) into duality.  It is not a normal thing to approach a double star by starting with the highest magnification you can use on a particular night and work backward from there — but my mind was still slightly scrambled from the beating it had taken trying to pry Xi (ξ) apart.  I plead temporary insanity caused by high frequency stellar scintillation.

The Nagler may have been a poor choice on this night — there was so much moisture in the air that the glow from the primary was sending shafts of light off to either side of the field of view.  If I hadn’t known better, I would have thought I was looking at opposing jets emanating from a black hole.  I had just used that same 9mm eyepiece to split Porrima a few minutes before — without that effect — so I presume it was just another measure of how badly, and quickly, conditions had deteriorated.  I had also looked at Porrima with a 9mm Meade Plössl, which came out a poor second to the 9mm Nagler, but I thought I would try it again now.  I made the swap, took a look, and saw that the opposing shafts of light were gone — plus, the image was a bit clearer.   Hmmm — just goes to show that testing eyepieces against each other is a risky business.

But there was no secondary visible in either eyepiece, so I started my backward battle and dropped down to a 12mm Brandon (125x).  Nope. Great contrast.  But no luck.

Next backward move was to a 14mm Radian (107x).  Still nothing.

So, I reached down into my eyepiece box, picked out a 16mm Meade SWA (94x), and replaced the Radian.  I was going from memory as far as separation and position angle were concerned, but I knew the secondary was relatively close.  At 94x, there was still an awful lot of hopping around in the eyepiece, but the main thing was the view was sharper at the lower magnification, and there was no problem with light scatter.

I peered and I looked and I searched and I averted vision and I nudged the focuser and I peered some more  …..  and then   …..   I saw it.  A faint dot of light at about 145 degrees.

Even in a six inch refractor, that barely there secondary will test your visual acuity.  But that strange shade of red, or orange, or maroon -- whatever it is, it's not of this world.  (East & west reversed to match the refractor view, click for a large version).

Even in a six inch refractor, that barely there secondary will test your visual acuity. But that strange shade of red, or orange, or maroon — whatever it is, it’s not of this world. (East & west reversed to match the refractor view, click to get a better view of the secondary).

Now with a difference of 6.6 magnitudes, that barely-there-secondary works out to be somewhere around four hundred times fainter than the primary — and a separation of 7.1 arcseconds puts it within the glow of the primary as well.  So I was filled with photonic thrill.

However, this was another instance of the focus having to be very precise — otherwise, that faint point of light would simply be engulfed in the glow.  Because of the poor seeing, the secondary would come and go as the atmosphere warped the focus back and forth slightly — kind of like looking at a rock beneath a shimmering surface of water — but I was able to hold it in sight for as much as a couple of a seconds at a time before one of the atmospheric waves moved it into another focal plane.

I put the legendary 12mm black Brandon back in for another look, and this time I managed to catch the elusive secondary a couple of times with it. But the atmosphere was working hard at hiding it, so I went back to the 16mm Meade and watched it shimmer in and out of view.

Now let’s take a look at Admiral William Henry Smyth’s (1788-1865) observation which is recorded on p.157 of Sissy Haas’s book:

“A delicate double star  … immediately above Xi  (ξ) … orange tint; cerulean blue, preceded exactly on the equatorial line by a 7th-magnitude star.”

The orange tint is the primary, which I saw as reddish orange.  And I saw the preceding seventh magnitude star — you can’t miss it. But what really intrigues me is his description of the secondary — “cerulean blue.”  I was amazed I could even catch a glimpse of it at all, let alone see any color in it.

I dug a bit deeper to see if I could find out what size scope Admiral Smyth was using, and the best info I can come up with is a 5.9 inch Tulley refractor.   If he used a larger one, I can’t find a reference to it.  Even in a six inch refractor, though, and with the eyepieces of that era (this is around 1830 or 1840), if he could see “cerulean blue” in the secondary, then I should be able to see it, too, with my six inch f10 refractor.

So guess what my current primal stellar urge is.

Meanwhile, may your April showers be few and the hail brief and merciful (and small).

Clear Skies, Star Splitters!

Advertisements

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: