1675: New observatory to aid sailors

On August 10, 1675, under the patronage of King Charles II, the foundation stone of the Royal Observatory is laid at Greenwich in London. The observatory was built to provide English navigators with accurate tables of the positions of the moon and stars for use in calculating longitude. In the 1750s, the Royal Observatory began publishing The Nautical Almanac, which established the observatory's site as 0° longitude, or the prime meridian. The almanac's popularity among sailors led in 1884 to the international recognition of Greenwich as the earth's prime meridian, making it the starting point for the world's 24 time zones.