Weather situation is clearly linked to observational activities of astronomical observatories.

If it is cloudy it is impossible to observe celestial objects, but weather conditions strengthly influence observations in other situations too. Recorded data’s quality, using a scientific telescope, is linked to atmospherical evolution above the telescope.

Everyone, who works into an observatory, knows what “seeing” means, we shall try to explain it.

Possibility to observe more night as possible during a year and to obtain images such good as possible to be studied, is linked to what is defined “seeing”. Our atmosphere behaves itself like an enormous lens in a continuous movement; this causes seeing phenomenon. Without atmosphere we should see images like sources

A star, which may be considered like a puntiform source, because of the distance from us, will appear like a luminous point. But it isn’t this way.

Light while crosses atmosphere, is scattered (because of refraction) each moment trough different directions.

What should appear like a point is observed like a small spot. Spot’s diameter is just what astronomers name seeing.

Smaller the dimensions of seeing is, better the observation is.

Seeing is a local phenomenon which depend on situation of the place (temperature, humidity, …); so it is clear because it is important to choose a good observative place and how it is important to verify constantly evolution of weather conditions too.