[LEAPSECS] Question about UT1 and the IERS Reference Meridian
Tom Van Baak
tvb at LeapSecond.com
Wed Apr 29 11:33:48 EDT 2015
BTW, this excellent question came to time-nuts yesterday; does anyone here have a definitive answer for Mike?
----- Original Message -----
From: <mflawson2 at cox.net>
To: <time-nuts at febo.com>
Sent: Tuesday, April 28, 2015 8:06 PM
Subject: [time-nuts] Question about UT1 and the IERS Reference Meridian
> Okay, I've tried to research this for a few days, and seem to be running
> into conflicting data.
> Some articles say that UT1 is based on the IERS Reference Meridian (IRM).
> Other articles say that UT1 is based on mean solar time at the Prime
> Meridian (Greenwich). It can't be both! Which one is it? In other words,
> which meridian would I need to stand on to indicate Solar Noon as
> 12:00:00.000 (UT1) on a day of the year where the equation of time is 0
> seconds offset?
> From what I can reckon, a 200-400 millisecond difference exists between the
> two longitudes, which are separated by about ~102 meters at Greenwich. So,
> if UT1 (and hence UTC) is based on the IRM and not the Prime Meridian, then
> at some point did clocks have to be adjusted ~200 milliseconds "away from"
> the Prime Meridian when the IRM was defined? Or was it sloppy and they
> treated the two as one and the same?
> Anyone know?
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