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Why the sky is blue and the sunset red: Rayleigh scattering and the length of the air The sky is blue and the sunset is red, yet the sunlight is the same. Air scatters short blue waves about four times more strongly than long red ones, a… Physics4 min read Why a cannonball fired hard enough never lands: Newton's cannon and the orbit Fire a cannonball horizontally from a mountaintop and it lands some distance away. Fire it harder and it lands farther. Fire it hard enough and the Earth's… Earth & Space4 min read Why astronauts float: the space station never stops falling Astronauts on the International Space Station look weightless, but at 400 km up, Earth's gravity is still about 90% as strong as on the ground. The trick is… Earth & Space4 min read