One of the most profoundly remarkable properties about our atmosphere is that it’s transparent to not only sunlight, but to starlight as well. As we turn our eyes skyward after the Sun goes down, a glittering tapestry of planets, stars, galaxies, and nebulae illuminates the heavens. If we want to view it, all we have to do is look with the proper tools.
But our view of what’s out there, from here on Earth, is limited in ways we rarely think about. Even on a cloudless night, any light coming to us from space must pass through over 100 kilometers (more than 60 miles) of atmosphere, which itself has continuous variations in density, temperature, and molecular composition.
Any light coming in has to contend with the atmosphere, and even though the atmosphere is transparent, that light inevitably gets distorted.