Can we define the present moment?

The present moment can be said to be the point where the unknowable becomes the known. The mind can know itself.
Mine does, and it has done so by becoming so familiar and cognizant of every arising all of the time that nothing is unknown. That is no thought, feeling, or thing is unknown. I have taken that to a deeper contemplation (its in one of these posts somewhere). Is that statement really true? Not exactly - there is new experience. The new experience right as it arises, is unknown. But because we have practiced and achieved a certain amount of mental discipline, honesty, and courage, we catch it and immediately (or almost) become familiar with it. That's called learning. What's special about that is that every moment is a constant process of learning, of the unknown becoming the known. That's why it appears so miraculous.