On Sat, 04 Dec 2004 19:50:53 -0500, RichA wrote:


That's why I hate winter in the North part of the U.S. and Canada.
The seeing is high-frequency boiling due to cooling of the ground.
Even if an object is high up in the sky, you see that horrible,
1-5 arc second shimmering. It kills planetary images. You have to
have days of cloudy weather, so the land can keep cool and then a
clear night to avoid it, and even then it never matches the seeing
you get in summer.

From Kansas City, I have logged numerous planetary sessions during
winter months --sometimes well below freezing-- where 1 arcsec or less
seeing was present for at least 20 or 30 minutes at a stretch. These
are usually periods where the upper level jet is not directly
overhead, yet upper winds in general may be well over 50 kts. And
summer around here can have weeks of 5 arcsec seeing on end.

Dan