J.A. Garcia-Barreto


Universal Time (from U.S. Naval Observatory)

Clock requires Netscape
Rotation of Earth around its own axis is not uniform: some evidence is a) Earth rotates slower in such a way that the current day is aproximately 16 milliseconds shorter than 1000 years ago; b) the positions of the north and suth pole change year after year and could contribute upto 30 milliseconds; c) there are regular and irregular fluctuations in the relative inclination of the Earth axis of rotation that would introduce upto milliseconds per year.

All of these facts contribute to the idea that Earth is an irregular time keeping machine and a definition of a Universal Time has been developed. Greenwich mean time or Universal Time as is also known, is the mean solar time as measured on the Greenwich meridian. Greewich meridian is that half of the great circle on the surface of the Earth passing through the north and south poles and through the reference point in Greewich, England. It is taken as the line of longitude 0 degrees. Over the years there are four definitions of Universal Time; those are:

Local time (Mexico City: Central Standard time)

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(Created: August 19, 1998. Updated: Dec. 09, 2002)