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Have you ever played with a pocket-sized laser, wondering how far its light would travel? Could you, a naughty student inside a classroom on Earth, annoy a poor substitute teacher on Mars by waggling your laser pointer at him?

T​he short answer: no. By the time the light finally reached Mars, the glint would be a million times dimmer than the faintest light visible to the human eye.

Read more insidescience.org

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