Lake Sonoma 11/17/08

Carter Scholz

Some smoke in the sky from fires south. A modest amount of cirro- cumulus overhead and to the west at sunset. Mostly the clouds moved east and skies were useable. Moonrise was at 9:40, so it was a shortish evening but satisfying, my first night out since Calstar. Temps stayed comfortable and humidity was low. SQL readings went from 21.14 to about 21.25; Lake Sonoma can be darker, but this wasn't shabby. Good Milky Way, though no zodiacal light -- unusual not to see it at LS -- maybe it shows more in the summer.

While waiting for full dark and clouds to move off I looked at the planets in the western sky: a slightly gibbous Venus very near a star, low enough to show atmospheric refraction; detail on Jupiter's bands indicated pretty good seeing (no GRS or transits visible); and Neptune showed through thin cloud a distinct though small disc. Uranus was not findable in the clouds and Santa Rosa light dome -- or rather, I couldn't find any naked-eye stars to hop to it from. (Pluto was also just above the horizon near Venus, but no.)

I began working from Alvin Huey's PDF book of galaxy trios. In Delphinus, 6928 was easy. 6930 took a while longer and required averted vision, but finally showed an elongated smudge. The third member, 6927, didn't show. Another trio in Del: 6956, star involved, somewhat large diffuse galaxy visible direct. After a while in this field I caught another glow, averted, coming and going, about 20% of the time. At first I thought it was just a star, and a star did show itself thereabouts, but this glow was separate. Checking against Alvin's labeled DSS print, it was in the position of UGC 11620, which he labels mag 14.6. This seemed almost incredible in these skies, so I asked Steve to verify. He saw it too. He commented that photographic plates don't have the same frequency response as the eye.

So that's interesting to learn about magnitude. Surface brightness makes for huge differences in visibility on extended objects, but I've been noticing that even on small galaxies (2' or less) where I would think magnitude is magnitude, it's not a strictly reliable guide to observability. In the Sierra this summer I was sometimes seeing fifteen-something galaxies and missing some fourteens in the same field. Not to mention that different sources give sometimes very different numbers. Got to start taking those numbers more flexibly.

Then into a neat galaxy group in Pegasus: 7619 and 7626 make a nice fat pair, with a mag-10 star to the N in a near-equilateral triangle (7') with them. Follow a line NE from 7619 through the star another 7' to find 7623. The other way on that line, 3' SW of 7619, is 7617, small and quite dim; appeared diffuse; came and went with the seeing. 15' SW of 7619, past a mag-11 field star, is 7611, somewhat easier. In this 30' field are four more NGCs, and one IC, and some others, but I couldn't see them.

Spent some time in the Pisces chain centered on 383, but couldn't fish out any new ones.

I was testing a couple of innovations: I had redone my light baffle, to get it entirely outside the light path, and I cut down the size. I cut it down too much. It worked fine with a 22mm EP, but the shorter EPs (parfocal) lost contrast. At one angle, Jupiter was quite a problem! I'd assumed: narrower field of view, smaller baffle needed. But it's the opposite.

On the plus side, I wrote an Astroplanner script to generate observing charts: one quarter-page is a 45-degree sky view, another quarter-page is a 5-degree finder view, and the remaining half is a DSS chart. This layout is stolen from Alvin's way of organizing his books, but now I can do it quickly and easily for any object. Takes a little more prep time, but this is a big win: only one binder to put on the music stand!

Steve shared views of some quite small PNs, about 2 arc-seconds, which showed dimension clearly even without a filter. Even, perhaps, the glimpse of a central star in one. At the end of the evening I got a nice view of 5 stars in the Trap through Greg's Mak at about 125x. The nearly-third-quarter moon came up orange in a thin band of cloud and we packed it in. A very pleasant evening.