Jupiter in a barometric marsh

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There is one situation favorable to good seeing that I did not talked about in my article Five good conditions for astronomical seeing, because its is rarer and more difficult to identify, the “barometric marsh”. That was the condition for me during the night from 3 to 4 December 2013, when I enjoyed good seeing on Jupiter.

The barometric marsh is meteorological situation where the pressure is relatively high, but outside any organized high-pressure : isobars are weakly visible, and winds are low. Here is the GFS map for the 4 December 2013 at midnight, France is between two HP’s:


Ground winds are extremely weak, so is the jet-stream above Nantes (I’m under the little violet patch at the center ;) ):


There was one drawback unfortunately as transparency was low because of the presence of thin high clouds. This does not deteriorate the seeing but the it does affect contrast a lot for short wavelengths. If IR or color images don’t suffer much, in blue and ultraviolet the diffusion of light was enough to deteriorate noticeably the resolution.

Click on the images to see them in full resolution.


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