[LEAPSECS] Question about UT1 and the IERS Reference Meridian

[Tom Van Baak]

BTW, this excellent question came to time-nuts yesterday; does anyone here have a definitive answer for Mike?

Thanks,
/tvb

----- 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?