Today, 29 February, is a unique day. So unique it happens, to a first approximation, only every four years.

But that, of course, depends upon what value unique has in your philosophy.

Scientifically today is indeed unique, in the formally correct sense. There is no other like it, for it will never occur again, at least as far as we currently understand the laws of physics which govern our universe.

Why? Because time, that ethereal quantity we measure in todays and years, is unidirectional and ever progressing. This time, this very instant, can never occur again. Hence it must be that this, and every other, today must be unique.

Enjoy your once in a lifetime experience!