Polaris – Double Star – Seeing the Companion With a Very Small Telescope, Maybe Even As Small As 30mm’s?
Polaris has never gained much attention as a double star. However, If you’ve had an interest in double stars, but never seemed to get started, Polaris would be a great double to start with, especially with a smaller telescope.
For this project, lets call a small telescope, anything 80mm’s or less.
Information from the “Cambridge Double Star Atlas” by James Mullaney and Wil Tirion, as a reference:
Polaris has a magnitude of 2.1 and the secondary or companion at a much fainter 9.0 magnitude with a wide separation of 19 arc seconds. The extreme difference in magnitudes can make this double more difficult to separate than you might think, especially if seeing is less than good.
Sometimes I check this star frequently, when setting up, to gauge seeing. I have some notes and sketches from years past, and current using some small telescopes.
July 1996: 4-inch Meade Schmidt-Cassegrain f/10, model 2045d: Seeing only fair, companion was not visible. Roger Ivester – North Carolina
September 1996: 4-inch Meade Schmidt-Cassegrain f/10, model 2045d: Seeing very good, could easily see the companion at 50x. RI
September 1996: 5-inch C5 Schmidt-Cassegrain, white-tube with the single arm fork. Made in USA. Easy, beautiful and clean. RI
February 1997: 4-inch Meade Schmidt-Cassegrain f/10, model 2045d: Seeing only fair. The companion was visible only intermittently. RI
October 1997: 90mm Meade ETX Astro-Scope, Maksutov-Cassegrain: Seeing was good and the companion was very easy at 52x. RI
December 1998: 102mm Vixen/Orion f/9.8 achromatic refractor: Very easy to see the companion at all magnifications. Roger Ivester
I was unsuccessful during the week of April 8th 2018, using my latest small economy Orion CT80 f/5 refractor. Seeing was only fair, so I’ll try it again in the next night or so. Roger Ivester
April 17th 2018: 102mm Vixen/Orion f/9.8 achromatic refractor: Seeing was very poor, could still see the companion, but only intermittently, using full 102mm aperture. Did not even attempt with an effective aperture of 60mm’s. RI
Mike McCabe of Massachusetts was able to see the companion last summer on a night of excellent seeing, using a vintage and classic Sears 60mm f/15 refractor.
Observing notes by Mike McCabe as following, for the night of April 18th 2018: It’s been great getting to know, Mike, who is a very experienced and skilled observer.
Notes from Mike McCabe:
Well, you really got my interest with your lobbying everyone to try and go see the secondary to Polaris with a small scope. I got lucky here last night – totally unexpected it was – with a clear and stable sky sometime around 9pm local time.
At first I turned my interest to the 10% waxing crescent moon, and I brought out my SV80ED to have a quick look. It was spectacular, with incredible earthshine on the moon and a dark, clear sky around it. There were nearly as many stars in the view as you’d see during an eclipse! I watched the moon occult a star (don’t know which one) and then toured the Haydes, the Pleiades and then Polaris. The 80mm brought out the secondary with no trouble.
I decided to bring out the Sears 60mm f/15. That was a good decision! I put Polaris in the eyepiece and ramped the power up to 112x. In short order I had the secondary in view at an ~5:00 position in the field of view.
I’ve assembled a 0.965 eyepiece kit, which includes a 40mm, 25mm, 15mm, 12mm, 10mm, 8mm and a 2x Barlow. I tried many eyepiece combinations, and must’ve looked at Polaris for an hour, and I could see the secondary from 60x all the way up to 180x. The best magnification occurred at 90x, with 75x being a close second. At 112x and higher it was still there, but more intermittently.
After last night I’m going with “it’s not only possible to see the secondary to Polaris in a 60mm telescope, but very, very doable.”
I have another 60mm f/15 OTA (a 1980’s era Celestron FirstScope) which I am currently setting up. I’m wanting to complete the Astronomical League’s Double Star list to receive my certificate which I started working on quite a few years ago, but have never finished. Mike McCabe – Massachusetts
March 2022: Using a 100mm f/5 achromat with an ES 11mm 82º eyepiece with the employ of a 2.5x Barlow (magnification 113x), I was able to view Polaris and its companion. Applying the 50mm sub-aperture mask allowed me to watch it continuously as the image dimmed, so that I would not lose the companion star. Having committed the star’s position to memory, I was then able to see it again without transitioning directly from the 4-inch aperture. The companion star is easily split in terms of spatial resolution, it’s really just the dimness that’s the problem. From a dark site I imagine it’d be easy to get down to 40mm or less and still see the companion. G. Brannon from North Carolina
April 19th 2018: 102mm Orion/Vixen f/9.8 achromatic refractor with an effective aperture of 60mm’s. Seeing excellent: 12.5mm eyepiece plus a 2.8x Barlow for a magnification of 224x. The companion was visible as a tiny bluish dot. Roger Ivester – North Carolina
April 19th 2018: Orion 80 mm (CT80) f/5 achromatic refractor. Seeing excellent: 12.5mm eyepiece plus 2.8x University Optics Klee Barlow for a magnification of 90x. The companion was visible as a tiny bluish dot. Very similar to the view using the 102mm reduced to 60mm’s. A beautiful sight in both telescopes. Roger Ivester
When observing with my CT80 or 102mm refractor, I always use a 1.25-inch correct image diagonal. For me it’s essential when sketching a deep-sky object, to have the correct orientation in the eyepiece field-of-view.
April 20th 2018: Orion 80mm (CT80) f/5 achromatic refractor. Similar conditions to my observation on the 19th. Using the same eyepiece combinations (90x) and was able to easily see the companion as a tiny bluish dot. RI
April 23rd, 2018: What? Observations seeing the companion with far smaller apertures than 60mm’s:
Polaris and companion:
“Celestial Objects For Common Telescopes” By Rev. T.W. Webb – 1859
“Spec. Bin., and slightly var. D., 9 blsh. as I see it. Common test, but only suited for small apertures, being easy with anything much exceeding 2 in. D. has proposed it as a general standard, finding that 80 on 2-in. will show it if the eye and telescope are good; he has glimpsed it with 1 3/10-in. achr. Dawson has glimpsed it with 1-inch. T. T. Smith sees it with 1 1/4-in. refl. In Dorpat achr. it has been perceived by day. De. gives it 8.4 m.”
1 3/10-inch = 33 mm’s
1 1/4-inch = 32 mm’s
1-inch = 25.4 mm’s
Just when I thought seeing the companion with 60 mm’s was really something, I received a telephone call yesterday PM (April 23rd 2018) from ATMoB member and friend, Richard Nugent.
Richard was using a 10-inch reflector with a 40mm off-axis stop-down mask, and was successful in seeing the companion.
The following is a photo of my 102mm refractor with a stop-down mask for an effective aperture of 60mm’s. I’m currently making a 30 mm and 40mm mask for the next clear night with good seeing.
Orion (CT80) 80mm f/5 refractor. Yes….I can see the companion to Polaris with this small short focal length achromatic refractor! My son bought this telescope for my birthday, and it will always be a prized possession of mine.
May 2, 2018: This was the third night in my attempt to see the companion using an effective 35 mm aperture. Seeing was only fair, and could not see the companion, nor with a larger 45mm effective aperture.
I’m thinking of a new plan, which is to make a 45mm and a 35mm off-axis aperture mask for my 6-inch reflector, and my 10-inch reflector. I’ve always had excellent results on difficult doubles using my 10-inch with a stop-down mask. I’ll continue to make entry posts. Roger Ivester
April 2nd 2018: Report by Richard Nugent
Roger, thanks for inspiring me to observe Polaris and it’s faint companion star, Polaris B. As I mentioned I’ve observed the pair more these past few weeks than in total over the last five decades! I’m glad I did. Here’s my report to date…
The challenge was to see if one could detect B using small aperture refractors. While I do own one or two refractors, it was easier for me to make an aperture mask to fit over the front of my 10-inch f/4.7 reflector. The mask offers unobstructed apertures of 90, 80, 70, and 60mm’s. A rotating cover allows me to change apertures very quickly and, with no obstructions, I get refractor-like images! When was the last time you saw Airy disks with your reflector? I thought so. As a bonus, the change to longer focal ratios produces exit pupils much smaller than the average eye’s entrance pupil. The eyepieces I chose to use were a 26mm Plössl (46x), a 16mm Nagler (75x), a 12mm Nagler (100x), and a 7mm Nagler (170x).
The seeing was a little better than average, perhaps 6/10 but with the aperture masks the seeing improved to about 9/10! Polaris B is about 19” away from Polaris so separation is not the issue. Seeing the B star only requires an aperture with a faint enough limiting magnitude. Of course, on any given night, a telescope’s limiting magnitude is dependent on many factors that are difficult to quantify. Limiting magnitude tables seem, to me, to be overly optimistic!
I had no trouble detecting the companion with the full aperture. I expected to have to ferret the star out of Polaris’s glare but the B star is about 19 arc seconds away and was very easy to see. And, after the view through the 10-inch I knew exactly where to look for it. I attached the mask and began with the 90mm aperture. The star was visible at all magnifications. Ditto using the 80 and 70mm apertures.
On to the 60mm. At 170x the star was very difficult and I suspected the magnification was a bit much for the sky conditions. Remember, 50x per inch, right? At the lower magnifications the B star was easy. It really helped that I knew where the star was. Honestly, if I hadn’t known where to look I’d would likely have missed it.
Next, I took a look at the moon. I grabbed my Meade QX 30mm Wide Angle eyepiece (40x, 1.5mm exit pupil, and a 1.75 ° true field of view) and…the view was nothing short of spectacular! The image was tack sharp, steady as a rock, and pleasingly bright. In all my years of observing I’ve never seen the moon look like that through any 60mm refractor I’d ever looked through! And then it struck me. I was using quality eyepieces filled with modern glass and superior coatings. I think if owners of small refractors invested in better eyepieces they’d use their scope more often and thoroughly enjoy each session. Even 0.965” refractors can be fitted with an adapter to allow for 1.25” eyepieces. The only concern might be some vignetting with wide field eyepieces.
The next day I let Roger Ivester know of my success with Polaris B and he wondered out loud — how small of an aperture might we go and still see the B star. That night was clear so I constructed 50mm and 40mm masks. I used the same eyepieces used the night before in addition to a Tele Vue 32mm Plössl. Also, I wanted to try some old school, 0.965-inch eyepieces. I have a box of “junk” and there I found a few eyepieces to try. None of these were branded but they are likely Tasco, 0.965-inch: SR5mm, H12.5mm, and H25mm. I also have a Meade 25mm modified achromatic. Huygens and Symmetrical Ramsden eyepieces are two lens systems designed in the 17th and 18th centuries, respectively. A Modified Achromat eyepiece is a 3-lens design similar to a Kellner eyepiece.
I first tried the 0.965-inch eyepieces with the 60mm mask. I had to hand-hold the eyepieces (my adapter wouldn’t fit into the focuser. Hmmm.) I could not see the B star with any of the Tasco eyepieces but I could just glimpse it with the Meade. I really tried to see the star with the Tasco eyepieces but I was not surprised by their performance.
With the 50mm mask in place I could not see B at 170x although the Airy disk of Polaris was very impressive! A bit later, upon close examination, I could see the companion only with averted vision and during moments of steady seeing. The star was easily visible in the other modern eyepieces. I attached the 40mm mask and could see the star with the 32mm and 16mm eyepieces! It was not visible at all with the 7mm eyepiece.
Two nights later I located Polaris 15 minutes before sunset using the full aperture of my 10-inch scope but I could see no trace of the companion. Later, despite the very bright moon in the sky, I tried a 30 mm mask. I could see the companion faintly using the 60mm mask but the star vanished when I flipped the 30mm mask in place. I went no further that night.
The bottom line: When using modern eyepieces a small aperture refractor can be a fine instrument. Upgrade your eyepieces and give it a try! Richard Nugent – Massachusetts
May 6th 2018: Report by Roger Ivester
Last night, seeing was excellent, and a 6-inch f/6 reflector, with an off-axis 45 mm effective aperture, could glimpse the companion, but with extreme difficulty. This required over more than an hour, using good breathing techniques, as it’s easy to “involuntarily” hold your breath, when attempting a close or faint companion, such as Polaris B. I also used an eyepatch over my non-observing eye, to relax my face.
It’s my opinion, it’s “next to impossible” to observe a difficult double (test) such as this while standing, neither have I been been able to observe any type of deep-sky object while standing.
I’m not planning to attempt anything smaller than 45mm’s. Richard Nugent of Massachusetts has the modern day record, or at least the only amateur I know personally, who has seen the companion with 40 mm’s. This was using a 10-inch reflector with a 40mm off-axis stop-down mask. Roger Ivester – North Carolina
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