When my brother Rick and I were in third grade, we had a teacher
named Mrs. Frankiewicz. Mrs. Frankiewicz used to say that she
never made mistakes—just once in a blue moon. One day, when she
wrote something incorrectly on the board, my brother pronounced,
“The blue moon has come!” (Genius then, genius now.) So “the blue
moon has come” is the Perlsteinian term for hell freezing over.