Well noted, Peter & Norman. I was not aware that GMT bumped the day at
noon...
It mostly mattered to astronomers, who didn't want to divvy up a night's
observations into two different dates. The epoch of the Julian day count
still starts at noon GMT on Monday, January 1, 4713 BC, proleptic Julian
calendar (November 24, 4714 BC, in the proleptic Gregorian calendar),
the start date of a large number of cycles and conveniently before most
precisely datable historical events except eclipses. The Modified Julian Date,
otherwise known as the VAX/VMS epoch, is the JD - 2,400,000.5, which
eliminates the half-day, therefore starting at midnight GMT on November 17,
1858 Gregorian.
Time Zones are not just the even 24 hours evenly distributed by geography
except for slight deformations for political boundaries, but are off by
quarter and third of an hour increments in some places.
Official time in extreme western China is about three hours off the Sun.
People in Kashgar/Kashi start work in the dark.
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