小常识：“本初子午线”是什么时候确立的？(视频)

Greenwich, a southeastern borough of London, England, has kept us on time as the prime meridian of the world since 1884. Time has long been of the essence of Greenwich, ever since Sir Christopher Wren designed the observatory there in 1675, which helped astronomers make precise time measurements through calculating the rotations of the Earth. The prime meridian forms the central longitudinal line from which world time is divided into 24 standard meridians, or time zones, each 15 degrees apart in longitude. Thus, American time is so many hours behind Greenwich, and Asian, so many hours ahead. Indeed, the world's time is set to this particular clock, which has been ticking since 1851, right up to this point in time.

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2010年12月CET【四级暑期特训班】