UTC isn’t a time zone, its a specification for how many seconds are in a day. In UTC, there are 84000 seconds on most days, but the IERS may announce a “leap se

UTC isn’t a time zone, its a specification for how many seconds are in a day. In UTC, there are 84000 seconds on most days, but the IERS may announce a “leap second” which makes some particular day either 84001 seconds or 83999 seconds (historically always the former).