minipost
Recently I gave a talk to an audience of non-scientists. During the question and answer section some asked "what's something important you'd leave us with?"
Everything you see is in the past. Light travels about a foot in a billionth of a second, so if you look at your feet, light takes five or six billionths of a second to make it to your eyes. You see your feet five or six billionths of a second in the past. The moon you see is one and a quarter seconds in the past, and the Sun about eight and a third minutes. The Andromeda galaxy, the farthest you can see without aid, about two and a half million years in the past.
I was going to point out it's more complex as it takes a few tenths of a second for your brain to register the image and the whole notion of "present" is imprecise, but that would muddy things.
Next someone asked for another useful piece of energy.
About a horsepower of solar energy falls on an average sized umbrella on a very clear day with the Sun directly overhead.
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