Heber Doust Curtis (1872-1942), US astronomer and a proposer of the extragalactic nature of other galaxies. From 1910, he studied spiral nebulae", which are now known to be other galaxies. By looking at the brightness of novae (stars which dramatically increase in brightness for a short while) in spiral nebulae, he concluded that they must be very distant. In 1920, he took part in a heated debate at a National Academy of Sciences meeting, in which he maintained that the Andromeda Galaxy lay a great distance outside our own, while his opponent, Harlow Shapley, refuted this. The matter was not settled until Edwin Hubble, in 1924, confirmed Curtis' theory."