[tz] Coordinated Universal Time (UTC) to retain “leap second”

[Marshall Eubanks]

On Fri, Nov 20, 2015 at 12:35 PM, Steve Allen <sla at ucolick.org> wrote:

> On Fri 2015-11-20T15:53:52 +0000, Paul_Koning at dell.com hath writ:
> > I'm puzzled.  Are there still marine navigators who have a sextant
> > at hand, never mind know how to use one, let alone active use it?  And
> > celestial navigation in airplanes disappeared, what, 50 years ago?
>
> The celestial navigation relies on an almanac.  If the almanacs were
> changed to tabulate according to "cesium atomic days" of SI seconds
> instead of "mean solar days" of earth rotation then everything would
> work.  The tricky part is getting everyone to agree to that change.
>
>
No, that will not work. The UTC clock is providing not just the time, but
also the rotation of the Earth (UT1). An atomic clock cannot do that (not
at the km level), and the tables cannot provide leap seconds (much) in
advance.

You have  a watch, radio, sextant. How do you find your position?

Set your watch by the radio, listening to WWV or some other station. That
time is in UTC, _which with leap seconds is an approximation to UT1, which
cannot be predicted (at the second level) more than a year or two at a
time_.

Use the clock, tables and sextant to find your position.

UTC was set up so that you can do this at the km level using a simple
shortwave radio anywhere on Earth.

Regards
Marshall



> --
> Steve Allen                 <sla at ucolick.org>               WGS-84 (GPS)
> UCO/Lick Observatory--ISB   Natural Sciences II, Room 165   Lat  +36.99855
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>
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