Astronomical seeing (units arcesec) refers to the blurring or instantaneous image broadening of astronomical objects caused by turbulent mixing in the Earth's atmosphere due to the variations of the

The useful time depends on the weather conditions at the Observatories, mainly wind speed, relative humidity, cloudiness and sky transparency (that is depending on aerosol and precipitable water

The water vapour (WV) is one of the constituent gases of the Atmosphere. Despite being a minor constituent, WV is a powerful greenhouse gas, with strong lines of absorption and emission in the IR