Double Stars by the Light of the Moon

by George Feliz

The prospect of clear skies outweighed the nuisance of the nearly Full Moon, and I had an enjoyable backyard session in Los Altos last night. Joe Bob had encouraged me to "check out" the Astro-League double star list, so I grabbed my TV85 (85mm, f/7 refractor) on a alt-az mount, two eyepieces and a barlow. I was also accompanied by my faithful Golden Retriever, Anna, and my not-quite-so-loyal cat, Teeka. The temperature was 44F and it was starting to get a bit damp.

The list of 100 doubles has few under 2", so the small scope should suffice. I am also familiar with a lot of them, so that should help. My 2 eyepieces were a 19mm Panoptic (32x, 2 degrees FOV) and a 9mm Nagler type 6 (67x, 1.2 degrees). I also had a 2x Televue barlow that saw a little use.

I started off with Polaris as I use it for adjusting my 1x red-dot finder, and knew that the seeing was pretty soft. Usually at 32x the mag 9 companion is pretty easy, but not tonight , although with the larger split at 67x it was clear. I did run into a problem, however. How do you figure out the position angle of the companion of Polaris? Usually I use Polaris to determine north, and the drift of stars in the field to set east and west. Anyone have a good way for an alt-az user to figure it out solely by observation?

After scratching my, er, head, I decided to punt on the P.A.'s for tonight. I didn't stick strictly to the order of the list because the moon was a large distraction, and guide stars were harder to pick out.

I ended up with 7 other doubles: eta Cas, gamma And, gamma Ari, lambda Ari, iota Tri, eta Per, and the Trapezium (does it count as 2?).

The best colors were on gamma And, lambda Ari and eta Per. My color perception is not great, but to my eye I saw yellow primaries and bluish secondaries on this trio. What colors do other folks see?

The tightest split was iota Tri at a modest 3.9" which was easy at 67x. The best matching was gamma Ari which to me were identical in brightness.

The Trapezium was really low and watery. It split well, but I would not be finding E or F on this night.

Saturn was also low and worth a glance, but it was mere caricature of the view we got up at Montebello on a recent rare night of excellent seeing.

I was nearly done with my short session, but for some deranged reason I thought back to a suggestion of Rich N.'s to look at the full moon when hunting craterlets in Plato. You never know if you don't try, so I increased the magnification to 133x and swung up to the Great Obliterator. Good thing I was only using 85mm of aperture, it reduced the beam to "stun".

After I got back on my chair, I swept around and actually enjoyed the ray patterns of Tycho and Copernicus. The seeing was better higher up so I focused on Plato. Sure enough, about 2/3rds of the time, the central craterlet winked at me. So I guess Rich wasn't pulling my leg.

Have other observers had success with Plato craterlets near the full moon?

It was a fine, short session, and I hope for better seeing tonight for a longer session.