MIKE AGLIOLO / SCIENCE PHOTO LIBRARY MIKE AGLIOLO / SCIENCE PHOTO LIBRARY
Time zones. Stopwatches and Earth on a starfield present an abstract image of Earth's time zones. The 24 international time zones were established in 1884. Each time zone represents an hour and occupies about 15 degrees of longitude, though the boundaries are bent to follow political borders. The system uses as it base the zero meridian of longitude, or Greenwich Meridian, (as it passes through Greenwich, London, Britain). The time along this meridian is known as Greenwich Mean Time (GMT). Time elapses as the Sun moves in a westerly direction, so the time zones to the east of the Greenwich Meridian are ahead of GMT and those to the west are behind.
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