[time-nuts] UTC and leap seconds
jimlux at earthlink.net
Fri Jun 11 17:46:45 UTC 2010
Hal Murray wrote:
> iovane at inwind.it said:
>> I was wondering, why we assume that Earth's rotation is slowing down,
>> instead that clocks are speeding up?
> The quick answer is that there is a mechanism that explains why the Earth is
> slowing down: tidal effects. There is no corresponding way to explain why
> atomic clocks are speeding up.
> How many different timekeeping mechanisms are there that are accurate enough
> to notice changes in the Earth's rotation?
> Wikipedia says 2 ms/100 years and that it was noticed by Halley in 1695 and
> confirmed by Dunthorne in 1749. I assume they were using the Earth's orbit
> around the sun as their reference clock.
how exactly would that work? Are they measuring the number of "days" in
a "year"? How would one do that? See when the sun crosses in front of a
specific star (to get the "day") (or an equivalent measurement at night
of some sort)
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