by Jay Reynolds Freeman
I went to Lick Observatory on September 23/24 for the Volunteer Appreciation Night. I will post a detailed observing report in due course -- with such treats as finding Einstein's Cross with the 36-inch, and a view of Saturn with the same telescope that featured both the brightness minimum half way across the A ring and the Division formerly known as Encke's, further out.
Yet my main reason for posting immediately is to facilitate comparison of the weather.
As I drove down 101 in late afternoon, it appeared that there was a lot of moisture in the air, visible as a general milkiness looking straight up, and further evidenced by occasional scud over high ground. Some of the scud was beyond the top of Mount Hamilton, which meant that cloud base was at least as high as Lick. There appeared to be cloud further down the Diablo Range, in the vicinity of Coe, as well.
I had not been sure whether I wanted to go to Lick or to Coe; my main objective was deep-sky observing with Harvey, my C-14, not touring Lick -- been there, done that. The decision was difficult, because of conflicting meteorological factors. Lick is higher than Coe, so if there had been upslope winds with cloud forming as the air cooled, Lick would get hit worse. On the other hand, Lick being high might give it the best chance of poking up through the cloud layer, and might minimize its susceptibility to leftover clouds if the weather pattern changed.
The weather was forecast to improve, and seemed to be doing so, so I picked Lick.
On arrival, there were no clouds above Lick, but the sky was still Milky, and a glance at the horizon showed a well-defined haze layer topping out a few degrees above the horizon; that is, the top of the haze was somewhat above Mount Hamilton. There was indeed some scud further down the range, but I couldn't tell whether it was affecting Coe or not. First thing out of my car was my electronic temperature gage and relative humidity meter. The temperature was 13 C, and the relative humidity was in the 70 percents, and climbing. As the sun set and twilight deepened, the humidity ascended to 89 percent, with dew atop cars and staff astronomer Elinor Gates worried about whether we were going to get to use the 36-inch at all. I started setting up my C-14, just in case, but left the OTA in the car for the moment.
Yet the haze layer was descending. I scaled the height of its top above the far horizon with my hand at arm's length. It went from two fingers' width, to one finger, to half a finger, and sure enough, as the haze layer went through the horizon, and passed below our level, the relative humidity started to drop. I completed setting up Harvey. Temperature did not change, but by the end of twilight, the relative humidity was in the low 70s, and at least some of the scud here and there had disappeared. It was too dark to assess conditions at Coe -- I couldn't see the range clearly.
Humidity continued to decline throughout the evening, and the wind stayed calm. At 0215 AM, when I started taking down, my gage read 12 C and 38 percent relative humidity. A fine night indeed.
Yet the haze and moisture was still there. As I drove down the road from Lick, I found myself in wetter air, with hazy sky above, by the time I got to Grant Ranch, and the valley lowlands near San Jose seemed wetter and hazier.
I am most curious how these conditions and developments compared with the experience at Coe; will someone please post details?