dipper@utastro.UUCP (Debbie Byrd) (10/13/85)
The line of longitude that runs through Greenwich, England, is called the prime meridian. More -- in a moment. October 13 The Greenwich Meridian A hundred and one years ago today a very important conference was going on in Washington, D.C. Delegates from around the world voted to make Greenwich, England, the site of the prime meridian -- the zero line of longitude. All other longitudes -- all positions east or west on the globe of the Earth -- are measured in degrees from the prime meridian. For centuries it has been easy for people to figure out how far north or south they are on the Earth. In the northern hemisphere, you can simply look at the north star. Where it is above your horizon is a measure of your approximate latitude -- your position north-south on the globe. But finding longitude -- your east-west position -- is more difficult. Finding the correct longitude depended at first on the invention of clocks that kept highly accurate time. With an accurate clock, you could keep track of the time at a specified point on the Earth -- even as you moved east or west of that point. You could then compare the time at the known longitude to your local time -- to find your longitude. Even after good clocks were invented, different countries used different reference meridians. The choice of a prime meridian was a diplomatic question. In the l880's most of the world's ships used the Greenwich meridian as their prime meridian -- the line of longitude that runs through the Greenwich Observatory in England. On today's date in the year l884, twenty-two countries of the world voted -- to make Greenwich the prime meridian. Script by Diana Hadley. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin