Hesiodus Ray, 3/17/97

Jay Freeman had posted a reminder that the Hesiodus sunrise ray (a ray of light extending across the crater Hesiodus from a gap in the wall it shares with Pitatus) was scheduled to occur at about 5:20pm on the afternoon of 3/17/97. Having failed to see the ray the last time it was visible (the first time I'd tried it), I wanted to try again this month. Unfortunately, at about 4:45, the clouds in Mountain View were so thick I could not find the moon, and I almost didn't bother.

Fortunately, it got better. At 5:20 when I got to Foothill College observatory in Los Altos, the moon was easy to find, though there were still quite a few high clouds. I found Pitatus and Hesiodus fairly easily (the far walls of Hesiodus were already well illuminated by 5:30) but saw no ray. It was challenging picking out any detail at all, though, in full daylight with clouds -- I kept losing the Straight Wall (usually obvious) every time I changed eyepieces. A thick band of clouds drifted across the moon and then stopped and sat there for about ten minutes. I was about to give up, convinced I was too late anyway since I could see Hesiodus already, when the band of clouds finally started moving again, so I went back to take another look, and at 5:45 the ray was well defined, all the way across Hesiodus, noticably spreading from the gap between the craters and where it hit the far end of Hesiodus.

I used Foothill's 6" refractor for all of this afternoon's viewing. (I'm not sure of the focal length so I won't quote magnifications.) The best view I got was with a 5mm Ultrascopic, which seemed to increase the contrast slightly over longer focal length eyepieces. My earlier searching, before the clouds moved off, was mostly with a 16mm Orthostar, because with anything shorter, I couldn't find Hesiodus, Pitatus, the Straight Wall, the terminator or anything else in the clouds. Once the seeing improved, the ray was visible in the 16mm and anything shorter, but not in a 28mm Plossl (though I expect it would have been visible in the 28mm with a darker sky or less haze).

I watched it for a while and spent 10-15 minutes making a sketch, then packed up to come back to work. The shape and extent of the ray didn't change noticably during that 15 minutes.