days plus 24 minutes and 44 seconds. Remarkably, the 37-sol period also accidentally almost divides several time quantities of interest at the same time. In particular: One Martian year is approximately equal to 18 × (37 sols) + 2.59897 sols Two Earth-Mars synodic periods are approximately equal to 41 × (37 sols) + 1.176 sols One Earth decade is approximately equal to 96 × (37 sols) + 2.7018 sols This makes the 37-sol period useful both for time synchronization between Earth and Mars timezones, and for Martian calendars, as a small number of leap sols can be straightforwardly added to eliminate calendar drift with respect to either the Martian year, Earth-Mars launch windows, or Earth calendars. List of notable events in Martian history Martian time in fiction The first known reference to time on Mars appears in Percy Greg's novel Across the Zodiac (1880). The primary, secondary, tertiary, and quaternary divisions of the sol are based on the number 12. Sols are numbered 0 through the end of the year, with no additional structure to the calendar. The epoch is "the union of all races and nations in a single State, a union which was formally established 13,218 years ago". 20th century Edgar Rice Burroughs described, in The Gods of Mars (1913), the divisions of the sol into zodes, xats, and tals. Although possibly the first to make the mistake of describing the Martian year as lasting 687 Martian days, he was far from the last. In the Robert A. Heinlein novel Red Planet (1949), humans living on Mars use a 24-month calendar, alternating between familiar Earth months and newly created months such as Ceres and Zeus. For example, Ceres comes after March and before April, while Zeus comes after October and before November. The Arthur C. Clarke novel The Sands of Mars (1951) mentions in passing that "Monday followed Sunday in the usual way" and "the months also had the same names, but were fifty to sixty days in length". In H. Beam Piper's short story "Omnilingual" (1957), the Martian calendar and the periodic table are the keys to archaeologists' deciphering of the records left by the long dead Martian civilization. Kurt Vonnegut's novel The Sirens of Titan (1959) describes a Martian calendar divided into twenty-one months: "twelve with thirty days, and nine with thirty-one", for a total of only 639 sols. D. G. Compton states in his novel