The best conditions give a seeing disc diameter of ~ 0.4 arcseconds and are found at high-altitude observatories on small islands such as Mauna Kea or La Palma.
The best conditions give a seeing disc diameter of ~ 0.2 arcseconds and are found at Dome C in Antarctica. Good conditions are also found at high-altitude observatories on small islands such as Mauna Kea or La Palma.