Star-Splitters

This second tour will take a slightly different course than the first one.  Whereas that one started with Albireo, an easy split, this time we’ll start with a more difficult double, Polaris.   After all, if you’re going to be a serious sixty millimeter Star Splitter, you have to work on your observing technique!  But after that, we’ll take a look at two stars which are easy to pry apart, and end in a mysterious, gray area, which comes close to defying rational explanation.

If you haven’t read the introductory post for this series, you might take a look at it here.

So strap yourself in — we’ off again!

Polaris holds down the north tip of the handle of Ursa Minor (Stellarium screen image with labels added)

Polaris
(Σ 93)  (H IV 1)
(Alpha [α] Ursa Minoris)
HIP: 11767   SAO: 308
RA: 2h 32m  Dec: +89° 16′
Magnitudes: 2.1, 9.1
Separation: 18.2″
Position Angle: 232°
(WDS 2009)
Dist: 431 Light Years
Spectral Type: F7
Rating: Difficult

So why are we beginning this second tour with a difficult star?  You really  didn’t think this was always  going to be easy, did you? 😉

Seriously, the reason I decided to start this tour with Polaris is because I start every session by looking at it — and since it’s a binary star, we might just as well see what we can see since we’re here already anyway.

If I’m using an equatorial mount, starting with Polaris is a necessity in order to get lined up with celestial north.   On the other hand, if I’m using an alt-az mount, I find it’s still handy to use Polaris in order to make sure my finder is lined up with the scope it’s mounted on.

Why use Polaris for that, you ask?  Because it doesn’t move!

At least not much for quite a while.  Actually,  if you want a real treat, take a look at the position of the secondary at the beginning of your evening, and then look again about four hours later — and you’ll find it’s moved very noticeably.  Really kind of neat — but then I used to listen to corn grow on hot summer nights in Ohio.

(But to be precise here, the motion you see is caused by the earth rotating on its axis, and that in turn is causing Polaris to appear to rotate very slowly around true celestial north, which is located about three quarters of a degree from the star.  Because the secondary is gravitationally attached to Polaris, it goes where Polaris goes — or in this case, seems to go).

And in answer to the question which I know is on the tip of your tongue  ……………….

“How difficult is it to see that beady little 9.1 magnitude secondary?”  …………………..

The definitive answer is  ……………………

Well, it depends.

When the seeing is poor — let’s call it a I or a II on this scale, it usually isn’t visible in a 60mm scope.  Or if the transparency is below average — again a I or a II  (I don’t have a chart to refer to, but it’s equivalent to the seeing chart) — you can forget it.

Otherwise, it’s there to be had, but it will take some judicious use of focusing talent to catch it.  First, look for a very faint, very barely there, pinprick of light.  Second — don’t overdo it on the magnification, or you’ll lose the secondary in the glow of the primary.

On the night I had the two scopes out for this series, the moon was about half full and over in the southeastern corner of the sky.  Despite that, the sky background was dark enough that I could see the secondary in both scopes.  In the 60/800, it was distinct, but faint, using the 20mm TV Plössl (40x).  I tried the 15mm version (53x), but almost lost it in the glare.

This is a pretty darn close match for what you can expect to see at the eyepiece, so look closely! (East & west reversed to match the view in a refractor, click to get better look.)

In the 50mm Zeiss, I could see the secondary — barely — using the 20mm Plössl (27x), but was able to see it a bit more distinctly with the 15mm Plössl (36x) and the 11mm Plössl (51x).  But still, it was just barely there — as in difficult.

The key in both scopes was a precise focus.  When you’re trying to see something this dim, there is a very critical focal point — meaning a very narrow range of focuser travel — at which that photon-challenged pinpoint of light will pop into view.  Go past it — and it’s gone completely.

One technique for prying it out of the dark sky is to bring the primary into sharp focus, then barely nudge the focuser in one direction, remove your focus fingers from the focuser to allow any vibration to settle down, then nudge again, and again, etc., until the secondary’s faint photons emerge.  If the primary starts to go out of focus, then refocus on it and try the other direction.  In other words, you need a more precise focus than can be achieved by focusing on the primary alone.

Another technique that works is to turn the focuser knob until the dimmest stars in the field of view become visible.  Experiment with that and you’ll find there’s a point at which they just begin to come into view — turn the focuser knob a slight bit more and they’ll begin to fade from sight.    Capture that point at which they first come into view, and then the secondary should be visible.  If not, try nudging the focuser just a very  slight amount in either direction.

You have to be patient!  You aren’t going to pry it out of the darkness unless you look long and hard and carefully.  Based on my experience, what will probably happen is that you’ll be staring into the eyepiece one night, and just when you’re about to give up, you’ll suddenly realize you’re looking right at it — which will prompt an outburst of this sort: “It’s really there!”   And it is.

What if you’re under severely light polluted skies?  I don’t have that problem — one of the most unnecessary evils mankind has ever inflicted on itself — so I can only guess.  But my guess is no, you won’t see the secondary.  The nearest experience I can compare it to is my skies under a full moon in the winter when the evil orb is almost directly overhead, bouncing its reflected rays all over the sky.  If — and it’s a BIG if  — the seeing and the transparency are a IV or better, I can usually just catch a glimpse of it.  But that’s only because I know right where to look.

If you don’t get the secondary on your first attempt, don’t give up.  With practice, it will pop right into view in a 60mm lens, and almost certainly when you least expect it.  Remember, you’re looking for a very FAINT, very SMALL, pinprick of light.  Once you’ve seen it the first time, and realize how small and faint it really is, you’ll have very little problem seeing it again.

But — if you didn’t see it this time, don’t despair.  Follow me to Cassiopeia — we’ll have an easier time there!

All three of the stars we’re going to look at in Cassiopeia can be seen on this chart –Alpha (α) and Eta (η) are at the top and near the center, and Iota (ι) is tucked in to the bottom near the right corner.   (Stellarium screen image with labels added, click to enlarge)

Alpha (α) Cassiopeiae    (Schedir)  (H V 18)              HIP: 3179    SAO: 21609
RA: 0h 40.5m   Dec: +56° 32′
Magnitudes:  2.4, 9.0
Separation:   71.2″
Position Angle: 281°   (WDS 2010)
Distance: 228.5 LY
Spectral Classification: K0
Rating: Easy to Moderate

Now the magnitudes of the primary and secondary of Alpha (α) Cass are almost identical to those of the Polaris pair.   But there’s one major difference — the two stars are four times as far apart.  That means it’s a whole lot easier to see the secondary.  And — even better (!) —  it will also give you a very good idea of what to look for when you go back to search out the Polaris secondary again — because visually, that secondary is a virtual twin of the Polaris secondary.

Easy to separate in a 60mm scope, easy to moderate in a 50mm scope, and a gold beauty in both scopes! (East & west reversed, click to see a close-up version)

I had no problem seeing the ninth magnitude companion with the 20mm Plössl (40x) parked in the 60mm scope.  It’s nowhere near as obvious as the 2.4 magnitude primary, of course, but it’s weak white point of light was beaming back at me very distinctly.  In the 50mm scope, though, you’ll find it’s noticeably more difficult.  I was able to pull it out of the primary’s glare with the 15mm Plössl (36x) with some persistent peering, but if you don’t see it at that magnification, try something in the neighborhood of the 7.5mm eyepiece (72x).

I rated this one moderate because of the disappearing act it might perform in a 50mm scope.  It’s easy in the 60mm refractor.

And don’t ignore the stunning color of the primary — it’s a gold beauty!

Eta (η) Cassiopeiae  (Σ 60)  (H III 3)              HIP: 3821    SAO: 21732
RA: 00h 49.1m   Dec: +57° 49′
Magnitudes:   3.5, 7.4
Separation:    13.3″
Position Angle:   322° (WDS 2012)
Distance: 19.4 Light Years
Spectral Classification: G0, K7 (Kaler)
Rating: Easy

Eta (η) is easy, easy, easy  ………..  and downright beautiful.  At the smaller apertures we’re using, the primary has a weak gold color, and the secondary displays a slightly darker and richer orange — both of which are welcome sights on any night at any aperture.

Easier than easy even — and the colors can be hypnotizing on a quiet, dark night. (East & west reversed to match the refractor view, click for richer color)

As an appetizer, I recommend the 20mm TV Plössl in both scopes (40x in the 60mm, 27x in the 50mm).  That places the two stars very close together, yet still distinctly apart.  Then, for the main course, work your way through your range of eyepieces until you reach a focal length similar to the 7.5mm Celestron Plössl — a heavenly desert of a view if ever there was one.

The 7.5mm eyepiece gives me 107x in the 60mm scope and 72x in the 50mm — and there’s plenty of light coming from these two stars to provide a bright, clear view.  But be careful here!  As you watch the two stars get farther apart with the increase in magnification and see the diffraction rings expand into view, you’re exposing yourself to one of the most addictive activities known in this sector of the galaxy.

And there is no known cure.

Iota (ι)  Cassiopeiae  (Σ 262)   (H I 34 — AB only)  (H III 4 — AC only)
HIP: 11569    SAO: 12298
RA: 02h 29.1m   Dec: +67° 24′
Magnitudes        AB: 4.6, 6.9    AC: 4.6, 9.0
Separation         AB: 2.6″           AC: 7.1″
Position Angle   AB: 229°  (WDS 2012)   AC: 116°  (WDS 2010)
Distance: 141.6 Light Years
Spectral Classification   A:  A5    B:  F5    C:  K1
Rating: Moderate to Difficult

Now I thought twice about even including this one — mainly for fear it might not offer an iota of a chance for someone new to this line of endeavor.  And here’s why.

About a year ago, when I was doing a side by side comparison test, I aimed two 60mm f/16.7 refractors at Iota (ι), using a pair of 17mm Celestron Plössls — one in each scope — that come from the same long line as the 7.5mm Plössl I’m using for this series.  Those two eyepieces gave me a 59x view, and that was more than enough to see both the 6.9 magnitude secondary and the 9.0 magnitude “C” star.

But when I turned the f/13.3 60/800 in use for this series on Iota (ι), I drew a blank.  Well, not a blank — the primary was obvious at least.

The culprit was poor seeing — about a notch below the I on this scale — in other words, really rotten.  Actually, the seeing may have been even worse than that.  Because for three consecutive nights, I could barely get the primary — or any other star, for that matter — to come into focus.  On the fourth night, using a 60mm f/15 refractor equipped with the 20mm TV Plössl (45x), the seeing was a rousing four — and all three stars threw up their stellar hands and appeared in plain sight without a fight.

A devil of an ordeal, but when you get it to cooperate, it’s a stunning little sight in a small scope! (East & west reversed once more, click to get a closer look)

I was about to go grab the 50mm Zeiss to give it a chance, but as I was trying to pull myself away from the stunning view of those three ravishing, alluring, siren-like points of light, I realized they were beginning to fade  —-  out  —-  completely.

Clouds.

They did it to me again.  Covered the whole darned sky.

Heavens to Zubeneschamali!  Been had again!  Rats!

But I’ve decided to include it anyway, as an object lesson in what seeing can do to your observing session.  On an average night, and certainly on a good night, you should be able to coax both of those close companions into view in the 60mm scope.  I’ll exclude the 50mm for right now — when I get another good night, I’ll give it a try and see what happens.

But back to poor seeing for a moment.

One night you’ll swear there’s no way under the stellar vault that whatever star you’re searching for can be seen — and the next night, it’ll be right there waiting for you in plain sight, grinning from one photonic edge to the other.  I’ve been doing this a long time — and after several nights of poor seeing, I still find myself beginning to wonder if my eyes are failing me, or if the scope has suddenly become incapable, or if the eyepieces are defective.  Suffice it to say, it can  —  and it will  —  play terrific tricks with your mind.

Don’t worry, though, you’ll get used to it.

Because when the seeing suddenly improves, and the veil is pulled back once again to reveal that elusive star in all its sharp, crisp, clear clarity — the frustrations will disappear.  Why?  Because your memory banks will be erased, reformatted, and replaced.  All you’ll remember is those distinct, gleaming, sharp pinpoints of light blazing away from in front of their velvet black background.

And now, if I could only remember what it was I was about to say before my cranial circuits were re-set  …………………………..

Oh, yeah  ………………   Let us not dawdle any longer!

Tour number three lies immediately around the celestial corner, so to speak, and I promise an astronomical improvement in atmospheric conditions!  Let’s go see what’s next!

Filed under: 2. Observing Tips and Tactics, 3b. 50mm Double, 3c. 60mm Double, Cassiopeia, Ursa Minor |