University Lowbrow Astronomers

Double Star Projects: The Spirit of 33.

by Collin McClain
Printed in Reflections: August, 2002.

Well it look like it was going to be a pretty good night for looking at the stars but it was almost a full moon so the deep space objects weren’t going to be as impressive as they are on dark nights.  So I thought I’d try and hunt down some double stars and see how many I could split with an almost full moon dominating the sky.  About a year ago I came across a website dedicated to double star observing, it’s called “The Spirit of 33 - An international network of double stars observers.”  http://www.carbonar.es/s33/33.html.  They have a nice list of observing projects broken down by constellation, “33 in Virgo”, “33 in Taurus”, etc.

I thought I’d try the 33 in Cepheus project.  There were several aspects of doing this project that I enjoyed so I thought I’d share them with you.  The first step was to lookup the 33 doubles and locate them on my Sky Atlas 2000.  I have the deluxe non-laminated version.  This allows me to circle the doubles on the charts and write in their names.  After locating all the doubles I then looked at the arrangement and came up with a strategy for the hunt.  Now I enjoyed using the transparent overlay with the grids that comes with the atlas, it’s the only time I use the thing.  But I realize this may not everybody’s cup of tea so the website does have star charts for some of the constellations.

By this time my telescope should have cooled off well enough and it was starting to get dark with the moon just starting to rise.  I noted that the moon had a very strange green glow when it was just coming up, I don’t know what could be in the air to cause that.  The first time I tried one of these 33 projects I used my XT8 DOB and had pretty good success.  But since then I’ve gotten an Intes MK66 Maksutov-Cassegrain on a GP-DX equatorial mount so I was looking forward to see how well the Mak was going to do with the harder doubles on the list.  The MK66 has a focal length of 1800 mm and I primarily used a UO ortho 12.5mm and a Televue Radian 6mm for the close doubles.

I picked Cepheus because it was at a good location in the sky this time of year.  One nice thing about these projects is that they’re confined to just one constellation.  This has the advantage of not having to point the telescope all over the sky and not having to perform the physical contortions sometimes required of an equatorial mount.  Plus it also gives you a chance to spend an evening on a single constellation, kind of a one on one up close and personal encounter with the King.

The project is a good exercise in star hopping.  I used a Telrad just to find my starting spot then an 8x50 right angle correct image finder star hopping with the manual slow motion controls.  I could make out only 7 or so stars in Cepheus naked eye.  I started at alpha Cephei and started looking for Struve 2764, a fairly easy double with a separation of 7.2 arc seconds and magnitudes 8.3 and 9.0.  A note on the observing lists from the website, most of them have a difficulty level, DI, listed for many of the double stars.  The site has a page, which describes how they use fuzzy logic to determine the DI values, which range between 0-100.  If anybody is interested or knows about that sort of stuff it might be worth checking out.  A quick summary, the DI depends on how close the stars are and the difference in magnitudes of the stars.  The greater the difference in magnitude the harder to split and of course the closer the harder.  For example BU 152 has a separation of 1.1” and a DI of 83.1 but Otto Struve 457 is 1.3” a little farther apart but a DI of 92.6.  The star magnitudes were 7.3/8.1 versus 5.9/8.1 respectively.

The website has a list as to how to classify the view of a double:

I don’t get quite so particular, I just use three descriptions:  no split, elongation, or clearly split.  The list had 3 that had a DI above 90, I clearly split the hardest one DI=95 but only saw elongation for the other two, 90 & 92.6.  Despite the full moon I had good success with the final score:  clearly split 29, elongation 3, no split 1.  I find that some of the nicer to look at doubles are pretty close in magnitude and are not real tight.  That night I noted that Struve 2863/Cephei 17 (8.5” 4.6/6.6) and Struve 2903 (4.3” 6.7/6.7) were quite nice.  It took about 2 hours to go thru the list so it’s a nice project for an evening.

I thought the MK66 perform quite well, there’s a kind of satisfaction using a quality optical instrument on a good mount and successfully hunting down 33 double stars.  Using the Radian 6mm gave me a magnification of 300x and a very nice star diffraction pattern.  A nice bright airy disk with the first ring somewhat well formed (the seeing wasn’t the best) and the 2nd and 3rd rings quite faint compared to the first ring.  On the closer doubles < 2” that I could split I could clearly see two separate disks and the first diffraction rings making sort of a figure eight.  Kind of cool to look at.

Another aspect of double stars is that sometimes there is a nice difference in the color of the stars with Alberio in Cygnus as the standard example.  Also in the process of star hopping around Cepheus I did see a few interesting groupings of stars and also came across a nice red carbon star, S Cephei.

So all in all it was an enjoyable evening and something I would recommend and I’m definitely going to try and complete the other constellations.  It’ll give you another reason to get the scope out especially on those nights with a full or near full moon.

Collin McMcCain (the author of this article).  Hoping for another clear Moon lit night to get back to some Double Star Splittin’.  Nice Article Collin! We all hope to see more!

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This page originally appeared in Reflections of the University Lowbrow Astronomers (the club newsletter).
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