Telescope Reviews: New Double Star Observing Project (II)

Finally had a chance to continue on with the project of checking a list of 30 double stars (taken from the Astronomical League's original double star observing club list), used as observing targets for the local club's beginners observing program. These pairs (and trios) were picked with the idea that they would be relatively easily located and observed by beginners using apertures as small as 60mm. (I’m using the 60mm f/11.8 refractor I’ve had since I was a teenager, now supported by an Orion AstroView EQ tripod and mount. eyepieces: 17mm Celestron SMA and 10mm Sirius Plossl.) In the set below I discovered yet another example of how, when compiling such a list, separation is not the only parameter that needs to be considered.

Observations made 19 June 2012. NELM 4.5 with moderately good seeing and a temperature at 9:00pm MST (4:00 UT) of 92°F.

24 Comae Berenices
I tell the beginners group here that one of the advantages of double star observing is the ability to observe these objects from home. No need for truly dark skies. If you can find them, you can observe them. 24 Com proved a good example of how finding the target (without GOTO) can be the challenge, not the observation itself. I found it quickly enough, but someone new to all of this, under comparable conditions, would probably need to work at it. In my small refractor the pair displayed a definite contrast in magnitude, with a warm yellow primary and a pale blue companion. The two were easily separated even at 41x. A good target for beginners, once they find it.

Kappa Bootis
Right at the edge of naked eye visibility, near enough to go straight to it with a finder scope. It was no challenge at all to split with the 60mm refractor, at 41x, though I found I liked the view better at 70x. No real colors were seen, with the primary a cool white and the companion a sort of grayish-white. I expect old time writers might have called the companion “ashy gray.” The magnitude contrast (4.6 vs. 6.6) was quite noticeable.

Zeta Coronae Borealis
Another one that flirted with naked eye visibility, and proved easily located. The components of this pair were pretty tight using modest aperture and relatively low (70x) magnification, but they were still easily separated. There was some contrast in magnitude, almost none in color, with both components having a sort of flat white look, with maybe a hint of blue to the primary. A good test for a beginner with a small telescope, but not what I’d call a show piece object.

Delta Herculis
Not a problem to find, being a third magnitude star and easily seen under my normal conditions. The trick was spotting the companion. The components are fairly close (for this telescope) but not to a degree that would ordinarily be a problem. The contrast in magnitude (3.1 vs. 8.2) presents a challenge. In that small scope the components were near enough that the companion was often lost in the glare of the primary (70x). At first glance, it seemed I’d focused on the wrong star! An example of why I tell beginners to be careful about trusting first impressions. The primary was white, and the companion appeared colorless – when it appeared at all.

Xi Scorpii
This proved to be an attractive and easy target for a small telescope. The magnitude contrast was significant, but not to the point of the fainter star being lost in the glare of the primary. Color contrast was easily seen, with the primary pale yellow and the secondary a cool blue. As a bonus, STF 1999 was also visible in the field, easily split at 70x and revealed as a pair of relatively faint, colorless stars of nearly the same magnitude.

Beta Cygni
Last for the night, though certainly not least. No challenge to find and observe with the Old Scope, but if I’m going to work this list, I should work all of it. Nice contrast in magnitude, beautiful colors of warm yellow and blue, and easily separated. The very definition of a show piece double star, whatever magnification I used. This is the probably the second double star I ever observed (many years ago), and is the one that introduced me to the concept of color contrast in double stars. Any excuse to revisit this old friend is a good one.