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On a related and equally fun subject, how fast are you going while you sleep in your bed tonight (and dream of walking a light-year)? - The Earth is 25,000 miles around and it takes about a day to go once around so its rotational velocity is 25,000 / 24. That means things on the Earth's surface near its equator are rotating about 1,000 mph. - The Earth's orbital velocity around the Sun is about 67,000 mph. - Our sun rotates around the center of the Milky Way galaxy at about 490,000 mph. Even at that speed it still takes something like 250 million years to go once around the center - a cosmic year. - Our Milky Way galaxy is moving through the universe in the direction of the constellation Hydra at about 1,340,000 mph. - (Maybe the new atom smasher will someday tell us that our universe is moving through something else at such a such speed.) So, adding all those up, you are moving not quite 2 million miles per hour while you sleep, or about .3% the speed of light. Three follow-up bonus questions. How much time dilation is that? How fast are you really going if you drive East going 60 mph? What happens if you roll the window down and stick your head out?