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by Bruce Jensen
Dave and Rebeka Silva, Adam Shiffman and his ladyfriend Malendia and I spent a beautiful evening, if a bit windy, at a "new" site in Sonoma County at Lake Sonoma, and Army Corps of Engineers facility and park. It was an extraordinary site, a bit longish on the drive (105 miles from my doorstep in San Lorenzo) but easy and fast, all highway miles, and VERY dark. The site we used was about 1,000 feet elevation, with excellent horizons all around except a clump of trees to the northeast about 15 degrees high, a flat well-graded native dirt lot with room for about 100 or 150 cars to comfortably set up, a clean and fresh portajohn, running water and picnic tables atop a pretty oak-studded hill. It is a near a road that leads to a campground, but the traffic was not heavy. The campground itself has a large group campsite that would accommodate probably 100 people for only $80 a night, but IMO it was not *quite* as desirable as this staging area (although it wasn't awful and one could leave their scope erected all day). Individual campgrounds, which have pleasant tree cover and close access to the lake, may be had for $16 a night. The campground has fancy toilets and showers, similar to many state parks.
To go there, one takes 101 north to the second Geyserville exit (Canyon Road), and follow the signs into the visitor center at the dam. From there, good maps show easy directions to a number if sites that could provide viewing, including the one we used. Our site was 10 miles from the highway exit on a good road.
The park has been used for some time by a few local astronomers, and some were there that night, but none were at our location and we were alone in that big parking lot. There are other sites in the park; perhaps next time we'll try one of those for comparison. The site we used sits atop a long ridge that separates the lake into two arms, so we had deep valleys on either side of us and the spine of the ridge extending east and west. The more northerly latitude of this park could have meant that another 3 degrees of usable southern horizon would be lost, but compared to Fremont Peak SW lot, the horizons are so good that much more sky is actually visible.
We started off with a pretty fair band of cirrus floating overhead, which gave us pause, but these proved to be inconsequential as darkness finally made them diminish to invisibility. The wind was a problem all night, but another astronomer told us this was very unusual, and considering this year's weather we had no reason to doubt him. There was no light dome from San Francisco, and there would have been nearly none from Santa Rosa if the moisture had finally fled from the air. As it was, Santa Rosa / Healdsburg made a dome about 30 degrees wide and varying between 15 and 20 degrees high depending on the presence of cirrus; in practice, this was a minor problem at worst. Elsewhere, it was so dark that Venus actually created quite a problem until it set; in fact, there was a sudden and noticeable change in the darkness at the precise moment it disappeared! The Milky Way was bold and detailed, nebulae that have typically been faint at other locations hit us between the eyes at this location. Brighter Messier objects (such as M104) were plainly visible in scopes as small as 6x30 finders. I'm not great at estimating limiting magnitude, but I can tell you that the sky was as dark as I've seen it at Fremont Peak on a pretty good night, and as good as San Antonio Valley on a great night. Had the cirrus left, the last bit of moisture dried and the wind died (essentially reasonably typical conditions), I'm certain we would have had mag. 6.5 plus skies, perhaps even 7 at the best times, overhead and all directions except southeast. Even with the wind howling, the seeing was not terrible, and at times was quite sharp (Mars, for example, appeared reasonably well defined in my 18" and deep-sky objects showed a wealth of detail easily, including mag. 13.8 Supernova SN1999cl in M88).
Oh, did I mention - it was FREE :-) no cover charge.
I fully intend to use this site again. I think that the darkness, the generally excellent horizons, the adequate minimal facilities and the easy drive all place this site near the top of the local sites list. I hope some of the South Bay folks will be willing to give it a whirl from time to time as well. Many thanks to Adam Shiffman for finding this underused gem for us.