Questions about seeing

[uhb1966]

Hi all,

last night i had an incredible seeing with a fwhm value of about 0.8 (800mm fl , qhy 8 w 6 megapixel). That is by far the best value i have ever reached. (yes , i am still  learning. ..)

Questions to the pros on sgl: do we have to have temperatures below 0 centigrade for great seeing? And how is it possible to have great  seeing when there is still  a lot of humidity in the air?

(i do understand that temperatures below freezing are good because there is far less movement in the air and that humidity drops when it starts to freeze. .. but i think there might be more to this???)

 

[vlaiv]

Not considering my self a pro, but will give it a shot

Seeing is dependent on many factors, but predominant few would be: jetstream and temperature gradient. I don't think there is need for sub zero temps in order to have great seeing, but often good seeing happens when there is a lot of moisture / haze in the air. Not because of it but rather same factors that contribute good seeing also contribute to poor transparency - no wind and high pressure - these help develop dewing and fog like atmospheric conditions, but also ensure there is not a lot turbulence in the air. There are also cases where transparency is good and seeing is good - but this is mostly dictated by geography of region - wind needs to blow from direction where there is flat surface - either sea, big lake, lowlands or some kind of plateau. In these conditions air flow is less turbulent and becomes laminar in nature - and if there is no significant temperature gradient - seeing will be good.

[uhb1966]

Hello Vlaiv, thanks a lot! That was very informative !