A universal calendar was devised by Gustave Armelin and Emile Manin, and was championed by the astronomer Camille Flammarion. It is made up of 52 weeks of 7 days each, and 1 or 2 "blank" days. These weeks, however, were divided into 12 months instead of 13 and grouped into identical quarterly periods: one month of 31 days followed by two months of 30 days. Each quarterly period began on a Sunday. The blank days were two "repeat Saturdays", one of which fell on 31 December every year and the other on 31 June once every four years.