[time-nuts] Re: UTC

Warner Losh imp at bsdimp.com
Thu Jul 28 18:20:59 EDT 2005

> The legal system in the US (and many other countries) is based on
> solar time, so it would break legal timekeeping.

It is only kinda based on solar time.  And only at certain locations, 

It is true that the definition of the time zones, in 15 USC 261
states, in part:

	the standard time of the first zone shall be based on the mean
	solar time of the sixtieth degree of longitude west from
	Greenwich... (and so on for each of the time zones)

"based on" can mean a lot of different things.  15 USC 260a
explicitly says that this time trumps any laws that the states may
have on an official time (later sections allow certain states to opt
in/out of daylight savings time, and define certain time zones).

However, there's some weasil words in the next section, 16 USC 262,
which seem to indciate that the actual legal time is determined by the

	Within the respective zones created under the authority of sections
	261 to 264 of this title the standard time of the zone shall insofar
	as practicable (as determined by the Secretary of Transportation)
	govern the movement of all common carriers engaged in interstate or
	foreign commerce. In all statutes, orders, rules, and regulations
	relating to the time of performance of any act by any officer or
	department of the United States, whether in the legislative,
	executive, or judicial branches of the Government, or relating to the
	time within which any rights shall accrue or determine, or within
	which any act shall or shall not be performed by any person subject to
	the jurisdiction of the United States, it shall be understood and
	intended that the time shall insofar as practicable (as determined by
	the Secretary of Transportation) be the United States standard time of
	the zone within which the act is to be performed.

The operative phrase being "as destermined by the Secretary of
Transportation".  It is up to this department of government to
delegate the definition to someone.  The time and frequency division
of NIST have this delegation, and provide the official time.  If they
say that the time is a little fast or a little slow, it is still based
on the solar mean time, but it isn't the solar mean time exactly.  The
US already doesn't observe exactly the solar mean time, but an
approximation of it based on UTC, as recovered by NIST.

I have not been able to find the actual regulations delegating this to
NIST (only statements to that effect on the NIST web site), so I'm
unable to tell how much deviation is allowed from the mean solar time
to still meet the statuatory langauge of 'based on'.  Clearly this can
be as large as 0.9s, since that's the standard that's been adopted
today.  But who is to say that it can't be more than that and still be
based on the mean time?  Without looking at the actual current
regulations that have been promulgated, it is hard to say, with
certainty, that eliminating leap seconds would break legal time.  I
tried hard to find them, but alas couldn't.

BTW, the 15 USC doesn't say anything at all about leapseconds or leap
seconds.  Maybe the politicians are the smart ones here :-)


More information about the time-nuts mailing list