Standing at the Centre of Time?? and Space
Greenwich Mean Time and the Prime Meridian
The Royal Observatory at Greenwich is the home to both Greenwich Mean Time (GMT) and the Prime Meridian.
Greenwich Mean Time (GMT)
Greenwich Mean Time was, for many years, the standard on which all other times in the world were based. The world is divided into 24 time zones, one for each hour of the day. A timepiece at the Royal Observatory kept the time on which all other clocks in the world were either directly or indirectly set. All of the other time zones were defined by the number of hours they deviated from GMT.
Prime Meridian 
The Globe is divided into 360 degrees of longitude, which are represented by the lines on a globe that run from the north and south poles. The Prime Meridian is the North-South line at zero degrees. Today a laser at the Royal Observatory indicates the Prime Meridian at night. The laser can be seen up to 16 km (10 miles) away.
Meridian and GMT Today
Navigational charts and sky maps today are still based on the convention that places the Prime Meridian at the Observatory in Greenwich. GMT was considered the fundamental time of the World until 1972, when Co-coordinated Universal Time (UTC) superseded GMT. Today some still refer to UTC as GMT. Because UTC still uses a system based on the Prime Meridian, the Royal Observatory is always the first place where a new day begins and an old day ends according to the world's time.
Submitted by: A. Wallen, Worcester Polytechnic Institute, 20 January 2007
