Keeping track of time is hard. Not only in terms of remembering meetings and be on time at the train station. Actually measuring time is a scientific art. Most of us find it logical to use the Earth rotation as a reference and define time scale and units from that.
If only the Earth would have been more cooperative!
It isn't rotating with a constant speed for starters and it adds a little wobbling on top of that, messing things up. With the user requirements of today's technology such as GPS satellites and internet, that is just not good enough to define UTC and we use the more consistent atomic time (TAI ) scale in parallell and adjust with leap seconds when needed. International Earth Rotation and Reference System Service (IERS) of the International Association for Geodesy is the international body that decides when and how much we need to adjust. You can find out more about the details here.
And I hope you remembered to synchronize your watches and added 1 leap second this New Years eve.
In the future I suspect we need to turn to the even more stable pulsars in order to meet the users need for precision and accuracy when keeping track of time.
