I read from different sources two seperate epochs for UTC. Which is
correct? Are the other epoch I mention here correct?

UTC epoch...  1 January 1601 or 1 January 1972?
NTP epoch...  1 January 1900
UNIX epoch... 1 January 1972
Microsoft epoch...1 January 1980 (but uses UTC internally? )

Harza,

 From das Buch, Chapter 13:

"Of the three heavenly oscillators readily apparent to ancient mariners 
and astronomers - the Earth rotation about its axis, the Earth 
revolution around the Sun and the Moon revolution around the Earth - 
none of the three have the intrinsic stability, relative to modern 
technology, to serve as a standard reference oscillator. In 1967 the 
standard second was redefined as �9,192,631,770 periods of the radiation 
corresponding to the transition between the two hyperfine levels of the 
ground state of the cesium-133 atom.� Since 1972 the time and frequency 
standards of the world have been based on International Atomic Time 
(TAI), which is defined and maintained using multiple cesium-beam 
oscillators to an accuracy of a few parts in 10^15 per day, or better 
than 100 ns per year. Since modern astronomy and space science needs a 
better interpolation means than Earth angular velocity, in 1984 ET was 
redefined as TAI + 32.184 s. As will be seen later, this requires some 
means to rationalize ET and actual mean solar time."

....

"The UTC timescale thus ticks in standard TAI seconds and was set TAI - 
10 s at 0h MJD 41,318.0 according to the Julian calendar or 0h 1 January 
1972 according to the Gregorian calendar. This established the first 
tick of the UTC era and its reckoning with these calendars. 
Subsequently, the UTC timescale has marched backward relative to the TAI 
timescale exactly one second on scheduled occasions recorded in the 
institutional memory of our civilization. Note in passing that 
leapsecond adjustments affect the number of seconds per day and thus the 
number of seconds per year. Apparently, should we choose to worry about 
it, the UTC clock, Gregorian calendar and various cosmic oscillators 
will inexorably drift apart with time until rationalized at some atomic 
epoch by some future papal bull."

Dave

Harza wrote:
> I read from different sources two seperate epochs for UTC. Which is
> correct? Are the other epoch I mention here correct?
> 
> UTC epoch...  1 January 1601 or 1 January 1972?
> NTP epoch...  1 January 1900
> UNIX epoch... 1 January 1972
> Microsoft epoch...1 January 1980 (but uses UTC internally? )

Thanks for the replies.

Unix keeps track of time by counting the number of seconds since its
epoch (Jan 1, 1970). Does WinNT/2000 operate in the same way or does
it keep track of the number of ticks since it last booted?


"David L. Mills" <mills@udel.edu> wrote in message news:<bfucjt$882$1@dewey.udel.edu>...
> Harza,
> 
>  From das Buch, Chapter 13:
> 
> "Of the three heavenly oscillators readily apparent to ancient mariners 
> and astronomers - the Earth rotation about its axis, the Earth 
> revolution around the Sun and the Moon revolution around the Earth - 
> none of the three have the intrinsic stability, relative to modern 
> technology, to serve as a standard reference oscillator. In 1967 the 
> standard second was redefined as �9,192,631,770 periods of the radiation 
> corresponding to the transition between the two hyperfine levels of the 
> ground state of the cesium-133 atom.� Since 1972 the time and frequency 
> standards of the world have been based on International Atomic Time 
> (TAI), which is defined and maintained using multiple cesium-beam 
> oscillators to an accuracy of a few parts in 10^15 per day, or better 
> than 100 ns per year. Since modern astronomy and space science needs a 
> better interpolation means than Earth angular velocity, in 1984 ET was 
> redefined as TAI + 32.184 s. As will be seen later, this requires some 
> means to rationalize ET and actual mean solar time."
> 
> ...
> 
> "The UTC timescale thus ticks in standard TAI seconds and was set TAI - 
> 10 s at 0h MJD 41,318.0 according to the Julian calendar or 0h 1 January 
> 1972 according to the Gregorian calendar. This established the first 
> tick of the UTC era and its reckoning with these calendars. 
> Subsequently, the UTC timescale has marched backward relative to the TAI 
> timescale exactly one second on scheduled occasions recorded in the 
> institutional memory of our civilization. Note in passing that 
> leapsecond adjustments affect the number of seconds per day and thus the 
> number of seconds per year. Apparently, should we choose to worry about 
> it, the UTC clock, Gregorian calendar and various cosmic oscillators 
> will inexorably drift apart with time until rationalized at some atomic 
> epoch by some future papal bull."
> 
> Dave
> 
> Harza wrote:
> > I read from different sources two seperate epochs for UTC. Which is
> > correct? Are the other epoch I mention here correct?
> > 
> > UTC epoch...  1 January 1601 or 1 January 1972?
> > NTP epoch...  1 January 1900
> > UNIX epoch... 1 January 1972
> > Microsoft epoch...1 January 1980 (but uses UTC internally? )