RSX-DEV@DEC-MARLBORO.ARPA (02/04/84)
Greenwich Mean Time is solar time at the the Greenwich Meridian; it varies with the variations in the rotation of the the earth. Coordinated Universal Time is an absolute time which can differ from GMT by almost a second. Leap seconds are inserted when convenient to keep UTC within one second of GMT. UTC is easier to track at independent locations on earth because all you need is the proper oscillator (I think the element used recently changed). To track GMT, you need an observatory. I've never heard GCT used related to time (I always thought it was Grand Central Terminal :-) --------
rpw3@fortune.UUCP (02/05/84)
#R:hou3c:-19700:fortune:28400001:000:710 fortune!rpw3 Feb 5 00:58:00 1984 And the reason it's called "Coordinated Universal Time" is because it was coordinated by treaty a few years back. I don't remember the year, but eleven or so nations all took leap seconds (ranging from -12 to +9 as I recall - the U.S. was -7 ???) to get together. All of their clocks were absolute time (not related to astronomy) based on either cesium beam or (ammonia?). Now we all take leap seconds together ("coordinated") as needed to stay close to astro time. (A "true history" would be nice, but probably in net.physics. Somebody?) Rob Warnock UUCP: {sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3 DDD: (415)595-8444 USPS: Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065