When Harold Urey in 1970 came to Lindau to give a lecture for the fourth and last time, the moon had been a hot topic for more than a year. The reason was, of course, the Apollo project, which brought the first men to the moon in 1969. Urey had already been interested in problems of the solar system, meteorites and the abundance of elements for many years. Already in 1952 he had put forward a theory of the origin of the solar system. So with the samples brought back by the astronauts, it was natural that he now focused his attention on the geological history of the moon. One way of investigating samples from the surface of the moon is to use radioactive dating methods. Since radioactive elements and their isotopes decay on many different time scales, one typically needs to find several “clocks” that “tick” with rates that fits the problem under study. This is where Urey’s old speciality isotope separation enters. In the beginning of the 1930’s, he developed a technique of fractional distillation to produce the isotope heavy hydrogen (deuterium). This isotope occurs at a fraction of 1 in 5000 in ordinary hydrogen and the same ratio appears in the heavy water formed with deuterium instead of ordinary hydrogen. Even though Alfred Nobel wrote in his will that he only wanted discoveries, physics inventions or chemical improvements done the year before to be awarded a prize, the rule is that you have to wait for many years before you are asked to come to Stockholm. Urey was asked already in 1934, but his answer was that he was sorry, but that he couldn’t come: His wife was due to bear a child in December. And, true enough, a daughter was born on the 10th of December, the Nobel Day! Thus, on photographs from the prize-giving ceremony of 1934, Urey is missing. On one of them, though, I recognize my grandfather Robert Bárány, who took part in the Nobel Day for the last time before passing away in 1936.