How Do Astronomers Know What Air Is Like on Other Planets?

MinutePhysics tackles the question of how astronomers know what air is like on other planets. Different techniques are used to measure the light either emitted or absorbed by gases in the atmosphere of distant planets, even ones not visible from Earth.

How do we know what the air is like on planets we haven’t visited? This video explains how to see air from 150 light years away.