RE: [LEAPSECS] name the equinox contest on now

From: Seeds, Glen <Glen.Seeds_at_Cognos.COM>
Date: Fri, 30 Jan 2004 10:05:36 -0500

The answer to your question is easy: it's only the apparent sun that matters
for UT. The rationale here is that we're looking for a time base that's
maximally useful to most people in the planet, for most of what they do. The
core of the definition of UT seems to satisfy this.

Of course, this time base is not suitable for ALL applications. Astronomy
needs a time base that's maximally stable the visible universe. GPS
and other duration-sensitive applications need a strictly linear time base.

Given the public availability of a strictly linear time base such as TAI,
the others can be related to it using their own combinations of fixed
offsets (e.g., GPS delta, time zones) and predicted periodic adjustment
(e.g., leap days and seconds).

Separation of concerns in this manner would allow the various communities to
control what matters to them, while still allowing them to communicate time
between them.


-----Original Message-----
From: Leap Seconds Issues [mailto:LEAPSECS_at_ROM.USNO.NAVY.MIL]On Behalf
Of Steve Allen
Sent: January 29, 2004 6:08 PM
Subject: Re: [LEAPSECS] name the equinox contest on now

On Thu 2004-01-29T18:01:04 -0500, hath writ:
> Of course, there is no "actual mean sun"; the luminous orb in the sky is
> "actual actual sun".

I would wryly ask whether you intend to refer to the "actual actual
sun" or the "apparent actual sun".

This is relevant to the question of why the epoch of ephemeris time
at the beginning of 1900 does not correspond to the moment when
Delta T was 0 (sometime near the beginning of 1902).

But if I did ask that I would be opening an old astronomical wound
about the constant of aberration used during the initial studies that
led to the creation of ephemeris time as a replacement for universal
time. And that's not to mention the light lag...

Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064      Voice: +1 831 459 3046
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Received on Fri Jan 30 2004 - 07:08:46 PST

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