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#Mon Aug 09 11:49:32 CEST 2010
Text__UBM6YKObEd-WfYQ0GneCwQ_title=Measuring the Earth
Text__UBM6YKObEd-WfYQ0GneCwQ_text=Since ancient times, the Earth is mapped using lines of latitude and longitude, which  facilitates the exploration of its surface and size. Well into the 18th century, longitude is  calculated exactly with the aid of eclipses of the moon, which are observed from two  locations that lie apart in an east-west direction. From the time difference between the  beginning of the eclipse at the two observation points, the distance of the longitude is  calculated. From the 15th century, the precalculated daily positions of celestial bodies are  written down in so-called \u201Cephemerides,\u201D which accompany sailors all over the world.