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How is zero longitude determined?
Arbitrarily - The Greenwich Observatory is currently
located at Cambridge University's Institute of Astronomy in Central England. However, the site of the observatory was originally in Greenwich, and was arbitrarily established in 1884 as longitude 0 degrees. The observatory was moved because London's fog made celestial observations difficult.
A plaque in the original structure marks the zero point from which longitude is calculated. The observatory was founded in 1675 by King Charles II to keep accurate tables of the position of the moon for the calculation of longitude by
English ships. Photographs of the sun were taken daily
at the observatory, conditions permitting, and a continuous photographic record of sunspots was kept starting in 1873.
Traveling at the speed of 186,000 miles per second, light take 6 hours to travel from Pluto to the earth.
"I am neither especially clever nor especially gifted. I am only very, very curious."
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