There are no leap seconds in universal time. There are leap seconds in UTC which bridges terrestrial time (SI seconds) with universal time (day = 1 earth rotation; second = 1/86400 of an earth rotation) by using SI seconds as the basic unit but introducing leap seconds here and there to ensure that UTC days stay in sync with terrestrial days (but not terrestrial seconds). This is why Date x Time ≅ DateTime for UT.
On Sat, Mar 14, 2015 at 1:24 AM, Jiahao Chen <[email protected]> wrote: > On Fri, Mar 13, 2015 at 1:01 PM, Stefan Karpinski <[email protected]> > wrote: > > Also, given that Julia time is based on UT, Time is well-defined – a > Time is > > conceptually an equivalence class of DateTimes that differ by exactly an > > integral number of days. If you think of a Date as the set of DateTimes > that > > occur during the same UTC day, Date x Time is naturally isomorphic to > > DateTime. > > I'm not an expert, but doesn't the existence of leap seconds in > universal time mean that the last statement is false? For certain > dates, it will sometimes be necessary to check if they harbor leap > seconds, so I don't see how there is a clean factorization of DateTime > into Date x Time. > > Thanks, > > Jiahao Chen > Staff Research Scientist > MIT Computer Science and Artificial Intelligence Laboratory >
