F-ckin Leap Seconds, how do they work?

Tony Finch dot at dotat.at
Tue Jul 3 21:35:13 UTC 2012

Peter Lothberg <roll at Stupi.SE> wrote:
> As the definition of a atomic second is 9192631770 complete
> oscillations of cesium 133 between enery level 3 and 4, "everyone" can
> make a second in their lab, that's TAI.

No, TAI isn't based on the SI second you realise in your lab. It's the SI
second realised on the geoid by a large fleet of clocks. If you are on
Mars then TAI isn't based on your SI second, because TAI doesn't tick at a
fixed rate relative to local proper time owing to the orbital differences
of the two planets.

> UT1-UTC is done by observations from radio astronomers VLBI telecopes
> and a comitee, you can't make one in your lab, and it's not real
> time.

You can make quite a good approximation to UT1 with a transit instrument
and knowledge of your position.

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Forties, Cromarty, Forth, Tyne, Dogger: Southeasterly 4 or 5. Slight or
moderate. Rain or drizzle, fog banks. Moderate or poor, occasionally very

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