Another Way to Polar Align

If you’ve been reading this blog for a while, you probably realize I thread my way through the night sky by star hopping.   There was a time when, like many other people, I used a Go-To mount and let it figure out how to get me to where I wanted to go.   But I soon realized I really wasn’t learning my way around the sky, which felt distinctly unsatisfying – kind of like relying on a GPS device to get you from point A to point B repeatedly without taking the time to learn the road and street signs you pass every day.   Given the fact that the skies above me are pretty darn close to magnitude six on a decent night, I decided there was no excuse for being lost most of the time when I looked up. It took a while, but I now know the constellations as well as I know my eyepieces, and there are parts of some constellations that are permanently etched into the corner of my mind reserved for maps.

But to be honest, if I was laboring under the typical light polluted urban sky, I would most likely have felt differently about the whole matter. My experience with light pollution and telescopes is limited to natural pollution, otherwise known as the full moon. It’s certainly possible to star-hop under light blasted skies, but I’ve found the typical 8×50 finder is limited to stars of about 6.0 to 6.5 magnitude when a full moon is hard at work refracting its rays all over a moisture laden sky. Under dark skies I can see stars as faint as 8.5 to 9.0 magnitude in an 8×50 finder, which makes finding my way around much less of a battle than it is when the moon is in charge of things.

If you use an equatorial mount, you quickly learned it needs to be aligned with the north or south pole in order to track an object in right ascension. If, like me, you have a motorized (tracking) EQ mount without GoTo capability, pointing it at Polaris will provide reasonably accurate tracking for most purposes.   But if you stay fixed on an object long enough, you’ll find it drifts from the center of the field of view, which requires you to use the mount’s declination controls to re-center the object.   For low-powered viewing, that’s not much of a problem.

But if the object of your attention requires high magnification, you’ll find yourself constantly re-centering it.   And if you’re trying to sketch the field of view, that perpetual wandering away from the center can make it difficult to accurately represent the stars in the field relative to each other. Which raises two questions: Why does it happen, and What do you do about it?

The answer to the first question is .75 of a degree, which is how far Polaris is from true celestial north. Which is another way of saying Polaris is really not quite the north star you thought it was. At low magnification, that .75 degree difference is minor, but with each increase in magnification, the quicker the object becomes unlatched from the center of the field. The more magnification you add, the sooner it starts to roam — somewhere around 200x you’ll see the object begin to take off almost immediately.   And if you’re a double star observer who finds 300x and 400x to be rather useful on occasion, you’ll find yourself constantly re-centering the object.

The answer to the second question – What do you do about it? – can be summed up in four words: find another north star. Or at least one closer to the actual celestial pole. As it happens, there’s a 9.65 magnitude star located a mere 13.5’ from true celestial north, which goes by several names: BD +89 38, GSC 04661-00002, SAO 3788, and TYC 4661-2-1. We’ll call it SAO 3788 since that’s the name most likely to be used to designate it.

If you’re beginning to feel a bit lost or puzzled, let’s take a look at Polaris in relation to the north celestial pole:

Stellarium screen shot with labels added, click to enlarge.

As you can see, Polaris is a bit shy of occupying the actual north celestial pole, which is the point at which all the lines converge.   But as you can also see, there are several stars which lie closer to the actual pole, one of which is the previously mentioned SAO 3788.

So now for the main question: how do you get to it?   You star hop to it, of course! Fortunately, we don’t have far to go, so if the idea of star hopping has you on the edge of your seat, despair not. You can do this quite easily from within the field of view of a wide angle eyepiece.

But before we get to the eyepiece view, there are a couple of things we need to pin down, the most important being the positon angle of the ninth magnitude companion of Polaris, which also serves as an important navigational tool.   In fact, we might just as well take a quick look at all the pertinent data on Polaris:

Polaris (Σ 93)  (H IV 1) (Alpha [α] Ursa Minoris)
HIP: 11767   SAO: 308
RA: 02h 31.8m  Dec: +89° 16′
Magnitudes: 2.04, 9.10
Separation: 18.10″
Position Angle: 233° (WDS 2013)
Dist: 432 Light Years
Spectral Type: “A” is F8, “B” is F3

Note the declination of +89° 16′ — further confirmation that Polaris is three-fourths of a degree short of celestial north, in case you still had doubts.

But the key number is the position angle, 233°. We’re going to use that as a reference point for determining which direction to move in order to aim ourselves towards the north celestial pole (which is at 360°). Determining celestial directions in the vicinity of the celestial pole is a very tricky business, even for the experienced observer, and it can be downright confusing when you’re gazing into an eyepiece.  The old trick of turning off your drive motor and letting a star drift across the field of view to determine which direction is west doesn’t work this close to the pole, so a navigational aid is a necessity.

Let’s start by imagining that the the line running from Polaris A through Polaris B stops at the edge of your eyepiece.   We’ll label that point 233°. When we subtract 233° from 360°, we get 127°, which is how far we need to move around the outer perimeter of the eyepiece in order to point ourselves towards celestial north.

Now we’re faced with the big question: which direction do we go? Clockwise or counterclockwise? The answer is that it depends on the kind of telescope you’re using, so pay close attention — it means the difference between success and frustration.  Assuming the use of a conventional inverting star diagonal (NOT an erect image diagonal), if you’re using a refractor or an SCT, north is clockwise from the 233° mark. If you’re using a reflecting telescope (Dobsonian, Newtonian), north is counter-clockwise from 233°. If moving by degrees around the outer perimeter of the eyepiece field is confusing, you can draw a line perpendicular (90°) to the line running between Polaris A and B and then add another 45° to that to point you toward north.

Here’s a diagram which should make all that more clear:

This may look simple when north and south are straight up and down, but that will seldom be the case when you peer into the eyepiece! Click to make the image easier to read.

And here’s how that move looks when superimposed on our previous chart:

Stellarium screen shot with labels added, click to enlarge.

Now that we’re directionally oriented in the eyepiece, there’s one more thing we need to discuss before going any further, which is how to move to where we want to be. If you’re new to this, it may come as a surprise, but it’s the mount that needs to move, NOT the telescope.

When you bought your mount, the instructions for it should have covered the procedures for lining up on Polaris. The first thing you would have done is set up your mount so that the declination axis was pointing toward Polaris, and then you would have used the altitude control to move the tilt of the declination axis so that it matched your latitude – in my case, that just happens to be 45 degrees. Then you would have centered Polaris in your finder by using both the declination and azimuth (horizontal) controls on the mount, and then fine-tuned that further by making final adjustments to center Polaris in your eyepiece. During that entire procedure, you would have left the telescope untouched.

So that’s what we’re going to do here.

With the counterweight shaft pointing straight up and down, and the declination circle lined up with the ninety degree mark, lock the declination and right ascension clutches on the mount and then use the altitude and azimuth controls to center Polaris, first in your finder, and then in your eyepiece (if your mount has locks for the altitude and azimuth controls, make sure to unlock them now – and don’t forget to lock them when we’re done!). Here are photos of two frequently used equatorial mounts, which will give you an idea of what to look for in the way of altitude and azimuth controls:

This is a Celestron CG4 mount. The altitude and azimuth controls are unlocked when one of the pairs of control devices is loosened, and locked when the two opposing devices are turned so they’re pressed tightly against one another. Other mounts, such as the CG5, have similar controls. Click for a larger view.

 

To unlock the azimuth and altitude controls on the Losmandy G11, just loosen the wing nuts shown in the photo — note there are two, one each on opposite sides of the mount. The Losmandy G8 uses the same setup. Click for a larger view!

All the movements we’re going to make from this point forward will be made using the altitude and azimuth controls on the mount.

Now if you look carefully at the chart above (here it is again), you’ll see there’s actually an easy way to star hop to SAO 3788. Notice that the Polaris A-B line points almost directly at 6.45 magnitude HIP 7283, which is distinctive because it’s bright and because of the ninth magnitude star located next to it (that star has a name by the way, SAO 223).   And if you move towards true celestial north from HIP 7283, you’ll see it leads you past 8.10 magnitude HIP 3128. And if you extend that line an equal distance, it just happens to lead you to our goal, 9.65 magnitude SAO 3788.

And here’s how that looks when diagrammed, minus the celestial grid in our previous chart:

Stellarium screen image with labels added. (Both this and the previous image portray the scene as it would be seen in a refractor or SCT, meaning east and west have been swapped).

Here are those moves once more, but this time plotted on our earlier grid:

Stellarium screen image again, click to enlarge.

So how does all that look in the eyepiece?

Click to enlarge – note, east and west are reversed here to match a refractor or SCT view.

This is the view with a 40mm Celestron Plössl in a 9.25 inch SCT. I’ve moved Polaris to the eastern corner of the field in order to pull HIP 7283 and HIP 3128 into the field of view.

If you now move toward the north until HIP 3128 is in the same position in the eyepiece as HIP 7283 was, you’ll see our goal, SAO 3788, come into view at the opposite (north) corner of the field of view:

Click to enlarge!

Center SAO 3788 in your eyepiece and you’re now a mere 13.5’ from true celestial north.   Once you’ve done this a few times, you’ll find it’s quick and easy to do.

I’ve found parking SAO 3788 in the center of my eyepiece is more than sufficient for a 400x view — I can barely detect any motion unless I stay on the object for ten minutes or so. Remember, we’ve gone from being 44’ off center from celestial north to 13.5’, which is a huge improvement.

Lock up your altitude and azimuth controls, unlock the declination and right ascension clutches, grab a 4mm eyepiece, and go split that pair of sub-arcsecond stars that’s been on your list for the past year without having to chase it across the field of view!

Happy star hopping and clear skies!

The Polaris (binocular) challenge – a learning exercise for new Splitters and a warm-up exercise for experienced ones

Polaris (Alpha [α] Ursa Minoris) (Σ 93)
MG: 2.0, 9.1  Sep: 18.2″  PA: 232°  (WDS 2009)

You can take this as a challenge, a lesson in splitting, or a warm-up exercise to use any time you feel like it  before moving on to something new.  For Northern Hemisphere observers Polaris is perfect in this respect because it is available every night, all night,  and stands virtually still. What’s more, it is not only a good challenge for binoculars, but also for any small scope.

Conclusions first

For me it has been all these things, but most importantly it has been a learning experience. I won’t keep you waiting – here’s what I have learned by taking the Polaris challenge:

• I can easily split Polaris at 30X
• I can intermittently split Polaris with 20X80 mounted binoculars in average conditions
• All the numbers we use  – I use – are approximations, so don’t get anal retentive about them unless you have done a thorough, optical analysis of your equipment. (Something that is beyond my knowledge and patience.)
• My binoculars say “20X80” on them. The effective objectives are really closer to 72mm, not 80mm –  that much I can measure.
• I have  developed a simple, sure-fire way to always know where Polaris B should be
• I have found that splitting nearby Mizar, with stars much more closely matched, but separated by 14 seconds instead of 18 seconds – is a great warm-up to splitting Polaris.
• All the other general rules for splitting apply in spades –
  • be comfortable
  • be well rested
  • be fully dark adapted
  • focus with extreme care
  • position your head carefully in line with the eye lenses
  • spend time on target
    • look for at least a solid minute at a time

And now the details – how I got there from where I was

I start as a 70-year-old star splitter who has never sought the challenges John routinely takes on, but who has over half a century split more double stars more times than I care to remember and at the top of my list of stars frequently split is Polaris. I do a lot of outreach and I almost always include it in the show, usually using at least a six-inch scope so my  visitors have no trouble seeing that little faint dot next to the second magnitude primary and reminding them then that if our Sun were placed at the distance of Polaris it would be a bit fainter than the  secondary – Polaris B.

Recently I finally made a breakthrough splitting doubles with binoculars – something that was a real eye opener for me – and I was hooked on the kind of delicate images – and  elegant splits you get at low power – or any time your splitting takes you into the realm of the improbable. So I had to see if I could split Polaris with binoculars. And I thought I did on my first try with 25X100 Zhumells – only when I checked our own web site to remind myself  of the position angle  (pa) of Polaris I found that my supposed split was simply wrong – way wrong – 180 degrees wrong!  Now that is embarrassing to an experienced star splitter – but it came because I was really under estimating what I should see and because I didn’t have an easy way to know where to look for Polaris B.

Knowing where to look is a special case – and I have since seen writings where experienced observers screw it  up – because Polaris is rotating around the North Celestial Pole just like every other star – so Polaris B will, in the course of 24 hours, appear to rotate about Polaris. All this means is to use the Position Angle of 232 degrees for Polaris you have to apply the same two rules that you apply to any star:

• west is the direction the stars appear to be moving
• north is the direction from the primary towards Polaris

Whoops! Can’t use that second one here because we’re looking at Polaris. So which direction is true Celestiual North when you look at Polaris? To answer that find the crude asterism known as the “engagement ring” – those  stars will always be to the south of Polaris and the position angle of the brightest star in the ring is darned close to the position angle of Polaris B – all of which should become clear as you study this chart.

Low power finder chart for Polaris B showing field for 20X80 binoculars. Polaris B is at almost the same pa as the star marked 64 - brightest star in "Engagement Ring" asterism. Click for a larger version. Developed from Starry Nights Pro screen shot.

The preceding chart serves as a guide in two keys ways – first, use it to know where to look for Polaris B.  The secondary is, of course, much closer to Polaris than any of the stars shown, but with a pa of 232° it is for all practical purposes in the same direction as the brightest star in the Engagement Ring marked 64. Using Starry Nights Pro software I measured the PA of that star from Polaris as 229° – so Polaris B is just a tad  west of this line.

Not rocket science, but not easy – it pays to sneak up on this one

Knowing that Polaris B is magnitude 9.1, it helps to first find the other numbered stars on this chart. The numbers follow the standard convention for showing magnitudes on a chart in that the decimal point is left out – so the star marked “90” is of magnitude 9.0. Since Polaris B is impacted by the glare of Magnitude 2 Polaris, I used the 9.8 magnitude star as my rough guide to know what to expect to see.

The next question was, however, just how close should I expect Polaris B to be – and for this I took two approaches. First, I did a warm-up exercise with a Televue 85mm. I started at 85X with a 7mm Nagler. My eyes weren’t fully dark adapted and the night was far from perfect, so it took a few moments for Polaris B to pop into view even at that power – but it soon was shining steady and obvious right where it is supposed to be and you wonder why it wasn’t always so obvious.  I then dropped the power systematically, staying on each step until I had a solid, positive identification.  I went to 66X, 54X, 46X, and finally 30X with a 20mm TV Plossl.  That was my lowest solid, consistent view for that session.  I could see it from time to time with a 25mm Sirius Plossl (24X), but I could not see it with a 32mm Antares Plossl – a better 30 or 32mm Plossl should have produced it, though – at least intermittently.

Actually, before I did this with Polaris, I shifted to Mizar and got a clean split right down to 19X using the 32mm Plossl.

The Mizar connection

Why Mizar? Well, it’s nearby, so the sky conditions are pretty much the same.  The two stars, Mizar A and B are much more closely matched in brightness at magnitude 2.2 and 3.9. And finally, the split is similar to that of Polaris at 14.3 seconds vs 18.2 seconds.  While this was a piece of cake for the scope, it’s a good challenge star for the 20X80 binoculars. They do split it cleanly, but it gives me a real good idea of how close I expect Polaris B to be to Polaris A when seen in those same binoculars.

The PA of Mizar's companion is indicated by the short arrow - I think of it as always in the general direction of the 7.6 magnitude star that forms a triangle with Mizar and Alcor. Click chart for a larger version. Prepared from Starry Nights Pro screen shot.

So I split Mizar first with the 20X80 binoculars and once comfortable with that split, moved on to Polaris without changing the focus.

The numbers are precise, but the measurements aren’t

We can be such fools for numbers – see the book “Proofiness.”  But don’t let the numbers associated with binoculars fool you.  They sound precise, but they aren’t.

But first, should you even expect to be able to split Polaris with binoculars? In this case you need to forget about  the usual answer to that question which starts with checking the Dawes limit. The Dawes limit for an 80mm objective is 1.4″   ( Dawes limit = 4.56 arc seconds/Objective diameter in inches.) Ha! Good luck. As star splitters know this is seldom achieved and of course there are  many other variables – local conditions, observer, and the difference in magnitude in the two stars, for example. These all have a significant impact on the true limit of what you can split leaving you with a rough, but useful guide.  However, when you introduce binoculars into the equation all bets are off – the Dawes limit moves from being a reasonable guide to being virtually meaningless.

I like the formula the Sky and Telescope columnist Gary Seronik uses. Because binoculars are low powered instruments, he has a rule of thumb that says the practical splitting limit for a binocular is 300 divided by the power.  By that rule the 20X80 binoculars should be able to split stars separated by just 15 seconds. The Polaris pair is 18.2 seconds apart and should fit comfortably into that rule. And, of course, the Mizar pair are a little closer together than that – and a fairly easy split, which is why I say all of these numbers are just rough guidelines.

What’s more, the numbers on your astronomy equipment may simply be wrong. In fact, the more I read, the more I am convinced that the numbers most of us take on trust and use as if they were absolutes are really approximations. This is certainly the case with binoculars, as Ed Zarenski has frequently reported on Cloudy  Nights over the years.  And Seronik, in the December 2011 Sky and Telescope, pointed this out with one simple test anyone can perform. Point a flashlight into the eyepiece end of a binocular and measure the diameter of the projected circle of light – that’s your effective objective.

Rough and ready flashlight test of the 20X80 Zhummel binoculars. The bright circle of light in the inset shows the working objective diameter the system yields for my particular pair. So while the lens may be 80mm, the effective objective is something closer to 72mm. Click image for a larger view.

If the effective objective measure is off by that much, then what about magnification? I suspect it is wrong as well, not to mention field of view. In fact, it seems like every time someone put a stock binocular to the test they find that in most cases all the key numbers tend to be on the high side. Doesn’t mean there aren’t accurate ones out there – for me it just means take it all with several grains of salt.

That’s one reason why I am not suggesting we have a contest to see who can split Polaris with the least amount of power – but I do encourage you to give it a try and report your results here in the comments after this post being sure to mention exactly what you were using by make and model.  And if you’re new to this game, don’t get discouraged. A decade ago I was feeling very satisfied to split Polaris at high power with a 6-inch!

As for me, I’m going to keep trying. The “intermittent” split I got last night isn’t good enough. I could only hold it for about 10 seconds at a time. What’s more, I want to try the 25X100 Zhumells again on this, plus the 20X60 Pentax – and  I have some 16X70 Fujinons on the way. These last are, according to the reviews I’ve read, really, really good. Wonder if it will make a difference? Since you’re only using the center of the lens, I suspect the inexpensive Zhumells are pretty good – but the Fujinons may do better because of better contrast – and the individual focus eyepieces should do a better job of finding and holding the best focus.

I’ll see. Meanwhile, I expect to use Polaris as a frequent warm-up exercise for star splitting, helping me to fine tune focus, get used to the correct eye position, and telling me when I am well dark adapted – not to mention having something to say about transparency and seeing on any given night.

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Touring the 50mm/60mm Skies, Tour Number Two: Polaris and Cassiopeia

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!

Pi 1 Ursa Minoris anchors an equilateral triangle inside a not-so-equilateral triangle

Pi 1 Ursa Minoris –  RA: 15h 29m   Dec: +80° 27′ MG: 6.6, 7.3  Sep: 31.7″   PA: 78  Spectral Type: G0, G8 subgiants Distance: 71 light years

Hmmm . . . I should be able to say something more about this easy double than that it’s a triangle inside a triangle – afterall, wherever you find three stars you can find a triangle of sorts. But John has been threatening lately to find doubles inside Ursa Minor and when he got distracted by other things, I decided I would take a look. Guess what? there are slim pickings here – especially for a 60mm. Sissy Haas lists only six doubles in Ursa Minor and uses a 60mm on only two, one being Polaris. Polaris, of course, is an exception, but it’s a challenge object for a 60mm, not, in my book, a “60mm jewell,” though it certainly is a gem in a larger scope. 

Pi 1 is not a challenge. You should be able to split this little dude with anything – even a telescope you got as a prize in a Crackerjack box! And in a 60mm, it’s actually quite satisfying. Hey, I’m going to call it a very subtle violet and green, though I suspect others see it as white and, uh, sort of white. (Yep – that’s what Haas says, though it’s spectral class might suggest a bit of yellow. Maybe “sort of white” is right.)

It’s also in a kind of fun area to explore. Start at Zeta –  that’s the fourth magnitude star that anchors the cup of the Little Dipper to the handle, then draw a mental line northward to the  next star in the handle, Epsilon.  Half way between these two, and a bit to the west, is a nice grouping of stars in the 6th-8th magnitude range. (Careful –  there’s a nice group of stars to the east also.) Part of the Pi group includes a triangle of 7th magnitude stars that fits nicely inside the 2 degree field of my 32mm Plossl when used on the 60mm Unitron (28X). And inside this triangle is a second, smaller triangle of 7th magnitude stars and this one is equilateral with its southern most corner being the double. But you don’t have to figure out which corner is to the south – just look for the double. The stars are pretty closely matched (6.6 and 7.3) and split by 32 seconds – a bit more than Albireo!

Wikipedia says this pair also has  an 11th magnitude companion, 135″ away. Didn’t see it. Well – didn’t look for it. Maybe another time.

Bet this field would make a nice sight in the 20X80 binos – have to give that a try!

Polaris (Alpha [α] Ursa Minoris)

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

After two weeks of constant clouds and rain (2.5 inches in the previous twelve hours), I woke up this morning at 3AM and discovered the moon was actually visible.  I poked my head outside and IT WAS CLEAR! Now this being the first week of June, that meant I had about an hour before the sun (if it actually dared to come out) began to brighten the sky, so I moved as quickly as I could, and by 3:30, I was set up outside and ready to go with a 76mm refractor.  I lined up on Polaris with a 25mm Plössl (48x), and despite the moon-brightened sky, I could clearly see the dim companion at about the eleven o’clock position.

That surprised me!  Normally in a 76mm scope it wouldn’t be quite that easy to see.  I switched to a 15mm Plössl (80x) for a different view — still there and very distinct — and then tried a couple of orthos I had just bought — a 12.5mm and a 9mm, both sold by University Optics — the “volcano top” variety.  That dim companion was still very distinct in both of them — really sharp in the 12.5mm (96x), and just a little bit more difficult to pick out in the 9mm (133x) because of some thin clouds and some moisture in the air.   Now normally I prefer the view of Polaris in a larger scope, mainly because the companion can be so difficult to detect.  But this morning, I was thrilled with what I could see in the 76mm Tasco.

Viewing Polaris with a 76mm Tasco – click on the image for a larger view!

Polaris has a yellow tint to it, and the companion appears to me to be white.  Actually, this is a triple star system, but it takes a hundred or more inches of aperture than I have to see that third star.  Polaris is also a variable of the Cepheid variety, but the change in brightness is not noticeable to the naked eye.  And although you can’t tell by looking, it’s a supergiant as luminous as 9000 suns, while the eighth magnitude companion has a luminosity of a mere 28 suns.  Distance to this system of stars is about 431  light years.

By now the sky was brightening considerably and the clouds were beginning to return across much of the sky.  I got a quick look at Mizar in Ursa Major and then a quicker view of Rasalgethi in Hercules, but lost it to the clouds before I could switch to a higher magnification.

Time to pack up and consider myself fortunate to have caught the sky gods napping.