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Jupiter this morning - 6th March 1918z
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Here's a copy of an email I sent to a colleague who lives about 15 minutes away. He was also up and observing jupiter this morning but found the view to be disappointing when he was looking (at about 5am). This was my reply:
"Jack, this morning the seeing was awful until about 5.30am, and then it improved steadily until it was quite good around 6.15am.
Bear in mind I only look at Jupiter in these sessions, part of the "seeing" that I find is related to it's altitude and relative location. I don't know what it was like elsewhere in the sky.
I nearly packed it in at 5am, the seeing was really poor. This can be predicted if you look at last nights temperature profile - it was unusually warm early in the evening, still 23C at 9pm when it should have been down to about 15C. Something was preventing the heat from escaping, I guess an inversion or some other impedance boundary was present in the lower atmosphere that trapped a lot of warm air and prevented the ground from radiative cooling.
Whenever this happens you can be sure the seeing will be appalling - both during the warm period when there is a nasty boundary layer present above you somewhere and also when this layer breaks and the heat starts escaping normally again you will get lots of convective turbulence in the air, also kills the seeing.
BOM was predicting an overnight low of 13C which was looking unlikely when I was still reading 20C at 10pm last night, but I took a gamble that the inversion would break sometime and the air temp would eventually equalise to the predicted value, so I set the scope cooling for 10C and went to sleep with the alarm set for 4am.
Well, at 4am the inversion was gone and the air was cooling rapidly, with the associated awful seeing that comes along. Luckily my guess was right, and by about 5.45am the air temp was down to 12C, and my mirror had slowly thawed from 10C up to 12C after I turned the cooling off at 4am. The turbulence abated and I got some reasonably nice images of Jupiter from 5.45 to 6.30 showing this mornings GRS transit. "
cheers, Bird
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