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.
Filed under: 4. Choose a Constellation:, Ursa Minor |
John Nanson
Greg Stone
Star-Splitters 
Polaris gave me a good example the other night of why you want a well-tuned scope of observing doubles. My 80mm Towa, which under good seeing certainly should have revealed the companion to Polaris, didn’t the other night because something is wrong with it.
I assumed it was a collimation issue, but that may just be a reflection of my ignorance. What I know is that it was taking all the light that normally goes into a nice set of diffraction rings and putting it into a single quadrant – and it happened to be the quadrant where the Polaris companion should be. As a result I could not see the companion.
What was interesting is it was producing a perfectly round and precise star image – it’s just that you had all this extra light in one quadrant – a whole set of quarter rings, instead of full rings.
I’d like to say the solution to this problem was to adjust the collimation, but on close inspection it turned out that the lens had other, more serious problems. Still, i felt it was a good lesson, telling me to get the collimation right, or suffer the consequences. Splitting doubles isn’t quite the same as splitting wood with axe – a scalpel maybe, but not an axe 😉
Position angle with Polaris fascinates me – I guess because Polaris goes around the North Celestial Pole like any other star, only we tend to forget that it does because, afterall, it is the “pole star.” When i want to know what direction in the sky is north, I draw a line between whatever star I’m looking at and Polaris – that is north.
When I’m looking for the companion of Polaris with a smaller scope the PA becomes important to confirm what you think you see. This morning I used a 76mm like John used in his report on Polaris. I didn’t find it quite so easy, but I did find it and I was sure because the position angle was correct. And how did I know the position angle was correct? It’s 233°, by the way, but how do you know where that is, since you can’t see the north celestial pole? How do you determine what direction is north from Polaris?
The answer I like is you draw an imaginary line between Polaris and Kochab, the brightest star in the cup of the Little Dipper. The North Celestial Pole is on that line, less than one degree from Polaris. So that gives you north and you simply count your degrees eastward from it. But there’s a short cut.
If you draw an imaginary line between Polaris and the star in the Little Dipper’s handle that is closest to Polaris, then you can figure that the companion star to Polaris is in almost the precise opposite direction.
Of course, don’t forget to compensate for your telescope flipping the image!
And why remember all this? Because Polaris is an excellent test object. It will tell you something about transparency, seeing, telescope collimation, the quality of your optics – even your dark adaption. And it does so while practically standing still. I return to it over and over and over again. But that PA has to be taken into consideration each time and in respect to a clock face, it’s constantly changing throughout the night and throughout the year.