Partly correct; what I said was that I've had the best planetary views during winter, not that the seeing was better as a blanket statement. When the weather is hot, the ground itself absorbs more heat during the day, and re-radiates it after sunset. It can take almost the entire night for the ground to reach thermal equalibrium during summer. It is at its worst over populated areas (lots of pavement & buildings) or rocky ground. The greater the "thermal mass" of the surrounding terrain, the longer it takes to cool. Short nights during the summer sometimes don't allow much observing time once the air settles down. Cold ground in winter considerably shortens this time, although if in a populated area you still have radiated heat from houses, chimney and flue plumes, etc. Generally, in winter, the air is more transparent than summer, however it is usually more turbulent. In summer, the air can tend to be more still, but it is dustier and less transparent. Obviously things are different during an inversion. Don't forget that during summer, the ecliptic is at a low elevation, and since all planets stay close to the ecliptic, (except Pluto) the seeing usually suffers for this reason as well. Any air convection going on makes the problem worse. I stand by my statement that I've had the best planetary views, by and large, in winter. Chuck --- Kim Hyatt <khyatt@smithlayton.com> wrote:

I think the notion that wintertime seeing is not as good as summertime comes from observers trying to observe near developed areas with buildings radiating their heat out to the universe, thus disturbing the atmosphere in the process.

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