• Notation
• Time zone
• Why bother

1. Notation

The international standard date notation is:

YYYY-MM-DD (e.g. 2002-12-25 (i.e. 2002-December-25)).

The international standard time of day notation is:

hh:mm:ss (e.g. 23:59:59).

2. Time zone

Without any further additions, a date and time as written above is assumed to be in some local (possibly unknown) time zone. The suffix 'UTC' indicates that a time is measured in Universal Time Coordinated:

2002-12-25 23:59:59 UTC

UTC was called Greenwich Mean Time (GMT) before 1972, however this term, strictly speaking, should no longer be used. Since the introduction of an international atomic time scale, almost all existing civil time zones are now related to UTC, which is slightly different from the old GMT.

NOTE: Where GMT is quoted, this in fact refers to UTC.

3. Why bother?

Using a standard time notation, allows anyone in the world to:

• know exactly what your time means, relative to, and regardless of, where they are in the world;
• easily and quickly convert your time into their local time;
• make calculations based on time, easily.

It is important to remember that not everyone, who has access to a web site, is living in the same month, year, or even century as the country hosting that web site.