Back Yard Astronomy: Double Stars in Cepheus
By Jay Reynolds Freeman

I hauled my 6-inch Intes Maksutov-Cassegrain into my Palo Alto yard on September 14, 1998, for Sissy Haas's double-star tour of Cepheus, from her article on p. 106 of the September, 1998, _Sky_&_Telescope_. The sky had been clear all afternoon, and stars were very steady shortly after dusk, which promised good seeing. Yet something in the feel of the air, and the dense covering of fog off the nearby coast, clearly visible in satellite images, suggested possibile moisture and sky cover.

I hadn't used the Intes in the several months since I finished my survey of the "big" Herschel list, for which it did yeoman duty. Lately, though, I have been leaving various telescopes set up handy for "quick-look" evening observing: With my Celestron 14 on a Losmandy G-11 mounting ready for star parties, my old Great Polaris is available for living-room duty, and now it was the Intes's turn to be mounted on it.

This six-inch Maksutov has excellent correction, and provides a lot of performance in a very small package. Its main disadvantage for quick looks is thermal settling time. I can circumvent that difficulty by planning -- I just put the optical tube assembly on the back seat of my car for a while before I observe -- but my session on the 14th was entirely impromptu -- I got home late from work, took the telescope out into 20 C cooler air than in my overwarm house, and started looking.

Fortunately, Sissy Haas's Cepheus list is composed mostly of wide doubles. I could resolve the majority with my 57x find-and-center-it eyepiece (Meade 28 mm Research-Grade Orthoscopic), notwithstanding that neither telescope nor atmosphere had yet settled. Several of these wide pairs are indeed very pretty. Delta, beta, and xi Cephei are all quite reasonable showpiece objects, and easy to find. Delta is the point star of the acute triangle that marks the south corner of the "square" part of Cepheus, beta is the opposite corner, and xi is right in the middle of the square. Cepheus is circumpolar from my latitude, so these stars are often well placed for observing. Furthermore, their declination, far from the equator, reduces their drift rate through the eyepiece field of an undriven telescope, so they are good star-party objects.

The Intes, however, had a driven mounting. I worried about using equatorial mountings in my yard -- there are so many trees that I am forever moving the telescope to chase after objects, so I anticipated that polar alignment would be a pain. Fortunately, that has not proved so. With polar-axis elevation pre-set to my latitude, and with due care to selecting reasonably level ground, I can eyeball the polar axis to within a few degrees of the right position as I set the telescope down, and that is more than sufficient for many minutes of visual observation.

The sidereal drive did help greatly with some of Haas's tougher targets, for which I was using more magnification. By the time I worked down her list to Struve 2843 and 2845, sky and telescope both were permitting the use of 187x, and Struve 2780 took 375x to resolve. All these stars might have separated with lower magnification, though -- I simply grabbed an 8 mm Brandon from my eyepiece pouch and added a 2x Celestron Ultima Barlow when I wanted more magnification. At 375x, seeing was good: The Airy discs of stars were continuously well defined, and the rings were usually visible, but always in motion. By this time, the sky above was hazy with moisture, and occasional low clouds drifted between me and the stars. Sometimes these conditions bring fine seeing.

At 375x, I was also able to separate all three components of Stuve 2764 -- Haas lists the B/C pair as 0.75 arc seconds and magnitudes 9.5 and 9.7, so the Intes was indeed doing well. The same magnification also showed a possible separation of the B/C pair of Struve 2872 -- the pair was certainly notched, but the seeing was not steady enough to let me say for sure whether the dark minimum extended all the way across the neck between the stars. Haas lists this B/C pair as 0.8 arc seconds, with magnitudes both 8.0, but with some suspicion that the actual separation may be closer. My observation is consistent with that notion: I found Struve 2872 B/C a good deal more difficult than Struve 2764 B/C, even though the latter pair is nominally closer, and has fainter components.

After I had finished Haas's list, I took a look at Jupiter, still a couple of hours east of the Meridian. At 187x, the planet was very promising -- the seeing appeared to be at least as good as we had had at Mount Hamilton a few weeks ago for the comparison testing of five-inch Refractors. Unhappily, the cloud cover had become so dense that it was difficult to see the planet at all, so I closed up for the night.

I have done a moderate amount of double-star observing in the past, but Haas works fainter than the limit of the old _Atlas_Coeli_ catalog from which I selected targets. Thus about half the stars on her list were ones I had not looked at before. It is nice to be able to step outside the front door and extend the limits of one's hobby. Even in the suburbs of San Francisco, back yard astronomy lives.

Maybe next time I will set up the Celestron 14.