Why is time with timezone 12 bytes?

All,

I was just checking on our year-2027 compliance, and happened to notice
that time with time zone takes up 12 bytes.  This seems peculiar, given
that timestamp with time zone is only 8 bytes, and at my count we only
need 5 for the time with microsecond precision.  What's up with that?

Also, what is the real range of our 8-byte *integer* timestamp?

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com