US astronomer Edwin Powell Hubble (1889-1953) photographed at the Mount Wilson Observatory, Los Angeles, California, USA. In 1923, Hubble profoundly changed our understanding of the universe by confirming the existence of galaxies other than our own when he observed Cepheid variable stars in the Andromeda nebula, proving it was a galaxy. He later introduced the classification of galaxies (spirals, barred spirals, ellipticals). In 1929, he announced Hubble's Law, which showed that galaxies move apart faster the further away they are, key evidence for the expansion of the universe.