A Blanket That Lets Light In

Before you start. One idea from elsewhere helps: everything warm gives off light of a kind our eyes cannot see, called infrared. Your Remote Throws Invisible Light - the EM spectrum tells how it was found; for this lesson it is enough to know that your body, a mug of tea and the ground all glow in it. Why the Ocean Is Blue shows a material swallowing some colours of light and letting others through; this lesson uses the same idea on air.