地理时间的使用始于大英帝国时期，当时用纬线和经线划分世界，零度经线通过伦敦的格林尼治天文台。
The geographic use of time began during the British Empire with the world divided by latitude and longitude, with zero degrees longitude running through the observatory at Greenwich, in London.
格林尼治国际标准以英国伦敦格林威治皇家天文台为准，也就是零经度为准。
Greenwich mean time (GMT) is mean solar time at the Royal Greenwich Observatory in Greenwich, London, England, which by convention is at 0 degrees geographic longitude.
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