There are moments in life when you realize, "Uh-oh, I'm not fresh-faced and 20-nothin' anymore." Like the moment you see a close-up of yourself and can't look away from the crow's feet. Or when you notice the first sun spot has emerged on the top of your hand.

And while I'm game to get older as gracefully (and with as much retinol) as possible, these photos of four sisters -- taken every year for 36 years -- kind of terrified me. To watch what the passage of time does to a lady in the span of 2 minutes inspired some nausea, I'm not going to lie.

The images, taken by the husband of one of the sisters, photographer Nicholas Nixon, are beautiful (if a little horrifying). They're so beautiful, in fact, that the Museum of Modern Art published a book presenting all of the portraits in sequence.

Keep clicking to see them here, then fill me in: What kind of thoughts are you left with after you watch the Brown sisters age before your eyes?