[fitsbits] Re: leap second alert

[William Thompson]

Patrick Wallace <ptw at star.rl.ac.uk> writes:

>On 15 Dec 1999, Paul Schlyter wrote:

>>       Usually one means UT2 when saying UT.

>I think UT1 is the more usual meaning.

	(rest deleted)

There's a good explanation of the different kinds of UT time at 

	http://www.maa.mhn.de/Scholar/times.html

which contains the statement

	Because of the availability of time standards that are more precise and
	easier to obtain (atomic clocks) UT2 has hardly any practical use. The
	Universal Time commonly adopted in astronomy is therefore the UT1
	scale.

Personally, I would expect UT to mean either UTC or UT1.  This is one reason
why letting UTC drift relative to UT1 is so troubling.

The computer industry tends to use the acronym GMT as a synonym for UTC, but
there's currently no exact recognized definition for GMT.  If they're so
worried about handling leap seconds in their software, they can define

	GMT = TAI - 32

(or whatever the value of TAI-UTC is when they freeze it).  The values of GMT
and UTC would start out in sync, but then would start to diverge as soon as the
next leap second was implemented in UTC.

William Thompson