Astronomical Seeing

Variations in Seeing on Star and Moon
Credit: NSO

Astronomical seeing is why objects in the night sky appear to blur and twinkle. The worse the seeing, the more they blur. It is changes in the Earth's atmosphere. which causes the seeing conditions. The less steady the atmosphere, the worse the seeing becomes.


Earth's atmosphere from the
International Space Station (ISS)
Credit: NASA

An Atmosphere is a thin layer of gas which surrounds a planet or moon. The gravity of a planet or moon holds the Atmosphere in place. Small planets and moons have low mass and a weak gravitational pull.  This means they tend not to hold onto an atmosphere.