Seeing the Invisible

What if you could see the way the wind blows? Or even the small changes in air movement or temperature in the room you're in? Derek Muller of Veritasium explains the process called Schlieren photography, which shows us those things that we can't normally see.

(YouTube link)

It boils down to concentrating an image of those invisible movements into a form that becomes visible to the eye. No, I don't totally understand it, but it certainly is cool to watch!