Time zones change for all sorts of reasons.
Daylight savings rules change.
Sometimes timezone offsets change, too, if nations redefine their time zone for political reasons.
The canonical time zone information database is the tz
or "zoneinfo" database, which used to be called the Olsen database. The zoneinfo DB is on the IANA site. There are a variety of programs to dump human readable versions of the DB.
You can use timestamp without time zone
if you wish to store a particular moment in wall-clock time, without concern for time zone.
timestamp with time zone
is sensitive to the system TimeZone
setting on input and output, and is stored in UTC time as absolute seconds. So it's converted for input and output. If you want different conversions or to override the conversion you can use the AT TIME ZONE
operator.