The Darian Calendar is a system of time-keeping designed to serve the needs of any possible future human settlers on the planet Mars. It was created by aerospace engineer and political scientist Thomas Gangale in 1985 and named by him after his son Darius.

Year Length and Intercalation

The basic time periods from which the calendar is constructed are the Martian solar day (sometimes called a sol) and the Martian vernal equinox year, which is slightly different from the tropical year. The sol is 39 minutes 35.244 seconds longer than the Terrestrial solar day and the Martian vernal equinox year is 668.5907 sols in length. The basic intercalation formula therefore allocates six 669-sol years and four 668-sol years to each Martian decade. The former (still called leap years even though they are more common than non-leap years) are years that are either odd (not evenly divisible by 2) or else are evenly divisible by 10.

Calendar layout

The year is divided into 24 months. The first 5 months in each quarter have 28 sols. The final month has only 27 sols unless it is the final month of a leap year when it contains the leap sol as its final sol.

The calendar maintains a seven-sol week, but the week is restarted from its first sol at the start of each month (ie the final sol of the week is omitted at the end of each 27-sol month). This is partly for tidiness, but can be rationalised as making the average length of the Martian week close to the average length of the Terrestrial week.

In the following table, the days of the week are Sol, Luna, Mars, Mercurius, Jupiter, Venus, Saturnus.

The last day of Vrishika is an intercalary day that does not occur in every year.

Start of Year

The Martian year is treated as beginning near the equinox marking spring in the northern hemisphere of the planet. 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 one hemisphere and masked in the other. The most sophisticated calculations of the Darian calendar extend to the point of making allowance for the slight increase in the length of the Martian vernal equinox year over several thousand years. These prescribe a more complicated intercalation formula (for details see the link cited below).

Disputed points

Certain details of the Darian calendar have been the subject of dispute. The greatest of these disputes surrounded the selection of the Martian epoch. Originally this was chosen as late 1975 in recognition of the American Viking program as the first fully successful soft landing mission to Mars. This selection came to be seen as excessively parochial, and also resulted in the many telescopic observations of Mars over the past 400 years being relegated to negative dates. The currently favoured epoch, first suggested by Peter Kokh, 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.

Nomenclature has also been a subject of dispute, although with somewhat less rancor. The names of the 24 months were provisionally chosen by Gangale as the Latin names of constellations of the zodiac and their Sanskrit equivalents in alternation. The 7 sols of the week, similarly, were provisionally named after the Sun, Moon and the 5 brightest planets as seen from Mars - including the Earth. These choices were also criticized as parochial. As a result, several alternate calendars, identical in design but differing in nomenclature, have been proposed. The Darian Defrost Calendar, for instance, creates new names for the Martian months out of patterns relating letter choice and name length to month order and season. The Utopian Calendar, devised by the Mars Time Group in 2001, has additional suggestions for nomenclature modification.

The calendar does not preserve the cycle of the days of the week. This would be unacceptable for members of religions that include the seven-day week in their beliefs. It was these religious grounds that prevented the adoption of the World Calendar. It would also be unacceptable for secular people accustomed to a two-day weekend, because the omitted day is always the Martian equivalent of Saturday.

Other Darian Calendars

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. In 2003, he created a variant of the calendar for Titan.

See also

• Time and date and astronomy on Mars

External links

• The Darian Calendar
• The Calendars of Jupiter
• The Darian Calendar for Titan