Stop and start

What a strange and frustrating start to the night. We opened well before sunset as usual but while I was outside our operator closed up again. I went inside and sure enough, the humidity was up at our warning level when we must close the dome (to stop condensation forming on the optics).

I went outside again, and five minutes later the dome was opened again. Great! Ten minutes passes by, and this time the dome is partly shut, the dome ventilation system (DVS) is closed but the dome slit remains open. Back inside to see what's going on and the humidity is close to our closing limit but not quite. The DVS was shut in case we had to close quickly, but the dome slit remained open to help cool down the dome. Off I went back outside again to take a few snapshots of the sunset.

After the sun had set (not that I could see it, it was behind a huge bank of cloud) we were just about to start observing and up goes the humidity again, so we have to close the dome again. Sigh. Our humidity was a couple of percent below the point where we have to close up, but the CFHT's humidity was much higher which I took as a warning that it wouldn't be long before our humidity would also be too high. 15 minutes later, guess what? Yes, that's right, the humidity was down again so we opened.

We had just started to actually observe and drat, who would have thought it? Humidity up again, close the dome and sit in the control room doing nothing other than watching all the weather information we have, and there's an awful lot of that! With no moon in the sky it was too dark to see what was happening outside, but my guess was cloud tops were passing through and being blown over the summit ridge and over us.

Finally, at around 9:30pm the moisture moved away and we've been working ever since. I'm glad this stop and start routine wasn't going to go on for the whole night...