Chuck Harris commented
Two leap seconds in as many years!
It must be that global warming.
-Chuck Harris
UT1 is the time measured with respect to the stars, while UTC and TAI
are based on the rate of laboratory atomic clocks; I like to say that
UT1 is the time you would read on your sundial.
Since the earth's rotation is an imprecise clock, UTC is a hybrid that
keeps your sundial's error to < 0.7 seconds (for the navigators, this
means <280 meters of east-west position error at the equator).
In case anyone is interested, here is the actual UT1-UTC data produced
by the group I headed for many years (until I retired in 2001):
[cid:[email protected]]
Here is what UT1-TAI (i.e. sundial - atomic clock) looks like without
the steps. The ~30 second offset represent the accumulated error from a
rather arbitrary historical date (1958, when the offset was set to 10.0
seconds). The GPS clocks run on GPS time, which is nominally the same
as TAI with a 19 second fixed offset (it was zeroed to UTC as of Jan
6, 1980, which is reckoned as the start of the GPS era).
[cid:[email protected]]
Regards, Tom
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