seeing
n. uncountablen. the quality of the air when you look through a telescope. If the air is steady, you can see clear details on planets; if it is shaky, the image looks blurry.
n. the atmospheric stability or turbulence affecting the clarity and steadiness of an astronomical image viewed through a telescope.
The seeing is excellent tonight so we can see Jupiter clearly.
Astronomers often travel to high-altitude deserts where the seeing is more consistent due to the thin, stable atmosphere.
Even with high-quality optics, poor seeing can limit a telescope's resolving power, as turbulent air layers cause the light from distant stars to shimmer and blur.
From see + -ing.
Probably an elision of "seeing that" or "seeing as".
Commonly used with adjectives like 'good', 'poor', or 'steady' to describe observing conditions.