How much does a shadow weigh?

Then again, a better question might be "how much less does an area covered in shadow weigh relative to surrounding areas covered in light?"

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As Vsauce's Michael Stevens explains in the video up top, light has energy. This energy allows it to behave as though it has mass, and enables it to push any object on which it falls ever so slightly. This behavior is the same thing that makes it possible to alter the orbit of the Earth with little more than a bulb, a stand, a shade and an extension cord. It's also the physical property that makes solar sails possible.

Cool, right? That's just the beginning. Set aside a few minutes and let Stevens explain some of the oddities surrounding the speed of light, the "speed of push" and photonic booms. You'll be glad you did.

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[Vsauce] [Device to alter the orbit of the Earth via Mark Rubin-Toles]

Videothumb via Shutterstock

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DISCUSSION

Corpore Metal

That was the strangest pronunciation of Cherenkov I ever heard.

Actually, most of the stuff this guy covered in the video I was aware of, except for flashes of Cherenkov light in the eyes of astronauts on the Moon. That was truly cool and never occurred to me before!

It makes sense though, Earth's magnetic field mostly deflects nearly all but the most energetic charged particles. Out by the Moon and in deep space there are no strong magnetic fields so it follows that cosmic rays and solar wind particles might occasionally pass right through the tissue of the human eye and make occasional flashes of Cherenkov light. That means when you're an astronaut sleeping on the Moon, even with your eyes closed, you might see very occasional flashes of Cherenkov light.

If I understand this correctly that is. I only just learned that this was possible a few seconds ago.