On Mon, 20 Jun 2005, David Berry wrote:
> One proviso on alignment of different time frames is that you cannot
> currently align two time frames if the alignment would involve the use of
> DUT1 (the difference between UTC and UT1). In practice this means that
> the supported timescales are divided up into two groups
>
> 1) TAI, UTC, TT, TDB, TCG, TCB
> 2) UT1, LAST, LMSG, GMST
>
> and you can only align a time frame with another from the same group.
The important distinction is that group (1) really are time scales whereas
group (2) are angles that describe Earth rotation. In fact Earth Rotation
Angle (and local ERA) could usefully be added to group (2).
The sidereal times in group (2) ought to be IAU 2000 compliant. Are they?
Patrick Wallace
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