[LEAPSECS] Nit-pick: SI second

Mark Calabretta mcalabre at atnf.csiro.au
Fri Feb 11 01:55:06 EST 2011

On Thu 2011/02/10 21:31:32 -0800, "Tom Van Baak" wrote
in a message to: "Leap Second Discussion List" <leapsecs at leapsecond.com>

>> A clock at the equator has a tangential velocity of 500m/s

>> whereas for one at the pole it is 0m/s. The difference,

>> amounts to about 100ns/day as per your later calculations.

>> This is the Sagnac effect of Special Relativity.


>Something's wrong here. The Sagnac effect as applied to

>clock synchronization is a time offset (a function of path

>and direction), not a rate (frequency offset). Its maximum

Consults references - yes, seems I was mistaken about it being the
Sagnac effect.

>Something else is wrong here too. National UTC timing labs

>are all over the world, at a variety of latitudes and altitudes.

>No one corrects for latitude as far as I know; only altitude.

>So I can't see why pole vs. equator would have anything to

>do with the SI second. Correcting only for elevation above

>the geoid I fully expect a cesium standard to keep the same

>time in Fairbanks as it would in Boulder or Paris, etc. Am I

>missing something? Should I start planning a new clock trip?

I can't see how they could ignore latitude. See Example 2 of
http://en.wikipedia.org/wiki/Proper_time as well as Rob's references.

I think someone already mentioned that GPS satellites correct for
time dilation, though their orbital velocities make for a much
larger correction.

Mark Calabretta

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