Lake Sonoma 1/17/09

Steve Gottlieb

Saturday night we had a nice group at Lake Sonoma taking advantage of this spring-like conditions. I arrived just after sunset and set up near Greg Laflamme, Bob Waltenspiel and Carter Scholz. Renato Del Rosario and Caroline Scolari were set up on the other side of me as were a few others. Conditions were nearly ideal for this time of year -- perfectly calm, very comfortable temps, low relative humidity, zero clouds and very good transparency for Lake Sonoma (several 21.4 on my SQM-L throughout the night). Even the seeing was better than average with sharp stars below -40 degrees dec where I was picking off galaxies early in the evening (the seeing softened a bit between 11 to 12). Really couldn't have asked for more at this time of the year. Most folks stayed until moonrise and left after 1:30, satiated with the yummy views.

I usually set a limit of -40 degrees dec for observing deep sky objects (particularly galaxies) at bay area sites but the last couple of months at Willow Springs I've been dipping down further south, bolstered by the excellent southern horizon and the extra two degrees southern latitude! (+36.7 vs. +38.7 at Lake Sonoma). Last month I was even able to do some exploring of the Vela Supernova Remnant at close to -45 dec. I thought I would try to continue plumbing the southern depths at Lake Sonoma though the brightest horizon light dome at this site by far is from southeast to due south, so I wasn't sure how this would work out. Fortunately, the sky rapids darkens from due south towards the southwest and if I waited until an object was barely west of the meridian, it was easy to pick off several 12th and 13th magnitude galaxies between -35 and -45 degrees dec in Fornax, Eridanus, Horologium, Caelum, Columba and Vela.

Besides galaxies it was good night for large, low contrast objects with striking views of NGC 1499 (California Nebula), IC 2177 and 6-8 degrees of Barnard's Loop. These were easy objects in my 80mm Stellarvue finder at 12.5x equipped with the appropriate filter, though of course they showed more detail at 73x in my 18-inch. Barnard's Loop was the last object I looked at before shutting down and while putting things away discovered that I accidently stacked two filters in my 31 Nagler -- an H-beta filter and a NPB filter. No wonder the background was so dark! IC 2177 winds its way from Monoceros (near Gum 1) south into Canis Major, ending near an easily visible reflection nebula. It stretches a full two degrees and the entire sinuous curve was easy to view in the 80mm using a NPB filter -- see

Last month Mark Wagner observed the starburst galaxy NGC 1569 in Camelopardalis and noted a pinpoint stellar core. Paul Alsing mentioned this was likely one its massive, young cluster (SSC = super star cluster) shown in this HST image -- Greg and I spent some time on this object at high power in my 18-inch. The brightest region in the galaxy is NW of center and contains two stellar or quasi-stellar knots (super-star clusters) within the glow. One of these "stars" is fairly easy and the other was occasionally visible. A very faint stellar object was also seen closer to the geometric center. These are likely the three non-stellar objects visible on the HST image.

Greg, Carter and I compared views in our scopes of two large Wolf-Rayet shells in Canis Major -- well known Thor's Helmet (NGC 2359) and the obscure Sharpless 2-308. Despite being a very good target for 10-inch and larger scopes Sh 2-308 isn't even plotted on the Uranometria 2000.0 atlas. With an OIII filter it displayed a fairly high contrast 25' western border that begins close south of mag 3.9 16 Canis Majoris and gently arcs to the north for nearly half degree with a slightly brighter patch on the north end. At the center is mag 6.8 EZ CMa, a massive star with a furious stellar wind that has carved out the nebula.

-- Steve

Observing Reports Observing Sites GSSP 2010, July 10 - 14
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Adin, CA

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