Time after Time

From: Daniel R. Tobias <dan_at_tobias.name>
Date: Sat, 22 Jan 2005 20:43:51 -0500

I sure hope that the future of mankind's timekeeping systems doesn't
get decided by an Internet flame war between contending groups of

As I see it, the dispute comes from the fact that people want two
different, irreconcilable types of "time", time of day (earth/solar
angle) and constant interval time.

Traditionally (over all of human history), civil time has always
related in some way to solar-angle time, originally directly, and now
in a complex, artificial way with confusing politically-imposed
irregularities such as daylight saving time and wildly gerrymandered
time zones. It still does relate to solar time, however, with the
local clock time at a given point on Earth at a particular time of
year generally fixed at a constant increment from solar mean time for
that spot (but sometimes changing to a different increment for part
of the year). There's no prospect that eventually, due to
discrepancies in the system, noon will come when it's dark (except
perhaps very near the north or south poles).

Some of the proposals, however, seek to decouple civil time
altogether from solar time, an unprecedented step which would
possibly lead to day and night being completely reversed; any "leap
hours" that prevented this would, if ever implemented, be even more
traumatic than leap seconds are now.

In addition to being historically unprecedented, such a move would be
illegal in the United States and some other countries, which have
laws explicitly defining their time zones based on solar mean time,
unless such laws were changed.

Now, if a time standard is to be defined based solely on constant SI
seconds, with no reference to astronomy, then why even include all
the irregularities of the Gregorian Calendar, with its leap year
schedule designed to keep in sync with the Earth's revolutions? It
really makes no sense that TAI includes days, years, and so on at
all, and this will seem particularly senseless when the current date
by TAI is a day or more removed from Earth-rotational time, as will
happen in a few millennia.

What is really needed is two different time standards: a fixed-
interval standard consisting solely of a count of SI seconds since an
epoch (no need for minutes, hours, days, months, and years), and a
civil-time standard that attempts, as best as is practical, to track
the (slightly uneven) motions of the Earth. When other planets are
settled, they'll need their own local time standards too (NASA is
already doing this for Mars).

== Dan ==
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Received on Sat Jan 22 2005 - 17:56:12 PST

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