For our younger readers, the Beatles were a rock/pop music group from the 1960's who had a few hit songs. The Christian Science Monitor looks back: It's exactly 40 years Monday since Americans first saw them standing on Ed Sullivan's stage, and writers still barely need to mention that John, Paul, George, and Ringo carry the surnames Lennon, McCartney, Harrison, and Starr. They were just four irreverent Liverpool lads who were determined to sweep America off its collective feet. But even they never quite figured out how a few minutes on television turned into one of the most significant events in pop-culture history - one that was witnessed by 73 million Americans.