The Danger of Shining Lights from the Earth Onto the Moon

Randall Munroe of xkcd and Henry Reich of MinutePhysics have made a cottage industry of answering stupid questions in a way that makes them ridiculously interesting. This is the What If? series. The question this week is whether we could change the color of the moon by shining a laser pointer on it if everyone on earth participated at once. The short answer is "no." But from there, these guys looked at the question as a challenge: what kind of light would actually make it to the moon? So they go through the various kinds of powerful lights we have, starting with a one-watt laser, which is already dangerous. Then we learn about all kinds of powerful lights we have developed but don't use that much because they suck up so much energy and can be deadly. Too much light isn't good for us, anyway. But certain powerful lights can actually reach the moon if we use enough of them! Sure, it's a dumb scenario, but I learned quite a bit about light technology in this video.