The Darian calendar is a proposed system of timekeeping designed to serve the needs of any possible future human settlers on the planet Mars.
It was created by aerospace engineer, political scientist, and space jurist Thomas Gangale in 1985 and named by him after his son Darius.
[2] Due to the use of 28 sol months, the Darian calendar has no mechanism for synchronization with Earth dates or with synodic periods.
[3] However, these static intercalation schemes did not take into account the slowly increasing length of the Martian vernal equinox year.
Mars currently has an axial inclination similar to that of the Earth, so the Martian seasons are perceptible, though the greater eccentricity of Mars' orbit about the Sun compared with that of the Earth means that their significance is strongly amplified in the southern hemisphere and masked in the northern hemisphere.
Gangale originally chose late 1975 as the epoch of the calendar in recognition of the American Viking program as the first fully successful (American) soft landing mission to Mars (the earlier 1971 Soviet Mars 3 Landing having delivered only 15 seconds of data from the planet's surface).
In 2002 he adopted the Telescopic Epoch, first suggested by Peter Kokh in 1999 and adopted by Shaun Moss in 2001 for his Utopian Calendar, which is in 1609 in recognition of Johannes Kepler's use of Tycho Brahe's observations of Mars to elucidate the laws of planetary motion, and also Galileo Galilei's first observations of Mars with a telescope.
Selection of the Telescopic Epoch thus unified the structures of the Darian and Utopian calendars, their remaining differences being nomenclatural.
[5] Suggested variations abound on the internet that use different nomenclature schemata for the days of the week and the months of the year.
In 1998 Gangale adapted the Darian calendar for use on the four Galilean moons of Jupiter discovered by Galileo in 1610: Io, Europa, Ganymede, and Callisto.
Gangale was inspired to create the calendar after reading Red Planet, a 1949 science fiction book by Robert A. Heinlein.