International Meridian Conference

The 1884 Washington conference that recommended Greenwich as the initial meridian for longitude and proposed a universal day.

Delegates from 25 nations adopted resolutions recommending a single prime meridian, longitude counted in two directions up to 180 degrees, and a universal day beginning at mean midnight at Greenwich. The resolutions influenced international practice but did not instantly impose one legal standard everywhere.

Modern geodetic zero longitude is realised by reference systems rather than the historic telescope line, and modern UTC is not identical to the astronomical time concepts used in 1884.