Quickly - recall three photographs that you will never forget - that have had an emotional impact on you. Don't intellectualize. Just let them come to you. Your grandparents' wedding portrait, a sonogram of a child inside you, the American flag being raised on Iwo Jima.
Whether a part of history or of our own lives, the moments captured in photographs stay with us. Chances are, most of them capture an indelible moment in our lives or in the lives of others.
So what is moment in photography?