On 2014-01-29, Skip Montanaro <s...@pobox.com> wrote: > According ato the pytz doc (http://pytz.sourceforge.net/): > > "UTC is Universal Time, also known as Greenwich Mean Time or GMT in > the United Kingdom." > > If they are equal,
The question is _are_ they equal? There is an exact defintion for what "UTC" is, and there's another exact definition of what UT1 is (more about this later). Civil timezones are defined as offsets from UTC. It seems that "GMT" no longer has an exact definition (at least from a metrologist's perspective) can be used to mean either UTC or UT1. UTC and UT1 can differ by up to 1 second. Leap seconds are occasionally added to UTC to keep it from drifting more than 1 second from UT1. >From a metrology point of view, what was originally called "GMT" (solar time at 0 degrees longtitude) is now called "UT1". So some people rightly claim that "GMT" means UT1. But nobody actually _uses_ UT1 (except metrologists and astronomers). All civil time is based on UTC: the official time in Greenwich (except during BST) is not UT1, it's UTC. So some other people rightly claim that "GMT" refers to UTC. In a software libary context, I would say that GMT should mean UTC and they ought to be considered equal and should always produce identical results. In a metrology context, people saying "GMT" probably ought to be smacked across the knuckes with a 12-inch platinum-iridium ruler and asked to try again until they specify either UTC or UT1 (or some other precisely defined UT-flavor). http://en.wikipedia.org/wiki/Universal_Time -- Grant Edwards grant.b.edwards Yow! A dwarf is passing out at somewhere in Detroit! gmail.com -- https://mail.python.org/mailman/listinfo/python-list
