ERICH SCHREMPP / SCIENCE PHOTO LIBRARY ERICH SCHREMPP / SCIENCE PHOTO LIBRARY
City lights. Artist's impression of a crescent Earth viewed from space with city lights showing on the night side. The velocity of the day/night boundary as the Earth rotates varies because the circumference of the Earth is different at different latitudes. At the equator it moves at approximately 1600 kilometres per hour (1000 miles per hour); at a latitude of 45 degrees it moves at about 1073 kilometres per hour (667 miles per hour). The Earth rotates once every 23 hours 56 minutes and 4.1 seconds.
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