the first leap year was in 1582
Royal Greenwich
The Royal Observatory is locates in Greenwhich The Greenwich Royal Observatory was commissioned by King Charles II, in Greenwich Park, Southeast London, England in 1675. Built by Christopher Wren, King Charles II appointed John Flamsteed to be the first Astronomer Royal. 'The King's Astronomical Observator' as Flamsteed was then known, was instructed by King Charles to apply himself with the most exact care and diligence to the rectifying of the tables of the motions of the heavens, and the places of the fixed stars so as to find out the so-much desired longitude of places for the perfecting the art of navigation.
Greenwich Mean Time, also known as GMT, is commonly referred to as the mean solar time. This measurement of time was first adopted in 1880 when it was used as the official time measurement in the United Kingdom. This was the time when the Royal Observatory located in Greenwich London was completed.
Edmund Halley was a hale and hearty type who was the second Astronomer Royal. He was disliked by the first Astronomer Royal, the Revd. John Flamsteed, who said; "Mr Halley smokes, swears and drinks brandy like a sea-captain". When Flamsteed died he had instructed his wife to sell all the instruments at Greenwich Observatory, and she did that, so that Halley had to start all over again in equipping the observatory. He is best known for his prediction that the famous comet would return every 75-76 years, and it did return, after Halley's death, and it was then named 'Halley's comet'. It was last here in 1986.
In 1912 Thomas Jaggar founded HVO (Hawaiian Volcano observatory)
The Prime Meridian based on Greenwich, England, is at 0 degrees longitude and all other meridians are "X" degrees east or west of it. The Prime Meridian was established for navigation and is the basis on which International time is kept. The International Date line is on the opposite side of the Earth from the Prime Meridian and is the point which seperates yesterday from today. The line was drawn by international agreement, and was skillfully drawn so as not to cross any land to keep all areas of a country in the same day (and time zone). There are few bends and kinks in the International Date line to achieve this, but if it was a straight line, it would generally be at 180 degrees E or W longitude. The Prime Meridian and the International Date Line are the two lines that separate the Eastern and Western Hemispheres.
Neptune
Greenwich, England
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According to the White House website Number One Observatory Circle is located in Washington D. C. overlooking Massachusetts Ave.
Madras in 1792
Royal Mail first delivered in 1666.