KEN CAMPBELL The Night Sky
...longitude was fixed at Greenwich England in 1884. Greenwich was chosen because of the astronomical connections set down by the likes of Isaac Newton and Edmund Halley, that enabled sailors to use the moon to navigate and fix their longitude more accurately. ... that local time would run more slowly at very high speeds. To test this theory an atomic clock was placed on board the Apollo rockets that travelled to the moon. On its return, the clock was found to be running out of sync with atomic clocks on Earth.