This is an implementation of the Darian Mars Calendar. The Darian calendar begins on 1609-03-1 18:40:34 UTC in the Gregorian Calendar. This is called the Telescopic epoch, because it is the first mars vernal (spring) equinox to occur before the first observations by telescope of Mars. This was chosen so that all observations from that point can be expressed in the calendar with positive dates. (Other more or less arbitrary starting points have been used for other calendars, among them the Julian Day Count and the landing of the Viking Lander. NASA’s Mars clock uses 1873-12-29 12:09 UTC (JD 2405522.0, Darian 140-19-26) as a starting point.)

The calendar is a 24 month perpetual calendar. Each year begins on the first day of spring (vernal equinox) in the northern hemisphere. Leap years happen on odd number years, and years evenly divisible by 10 and 500, but not by 100. Each month has 28 days, except for the last month of each quarter (6, 12, 18, 24), which have 27 each. (The last month has 28 on leap years.) The 27 day months skip the last weekday so that each month begins on Solis, and any day of the month is on the same weekday every month.

The month names are based on the 12 constellations, but since there are 24 months each one is used twice, first with its Latin name, then with its Sanskrit name. The names of the weekdays are from the original Latin. Various methods of noting the time of day have been used with this and other calendars. Here I opt for a straight-forward decimal time, to five decimal places, shown below the Today date. This is the current time at Mars’ prime meridian (defined by the location of the crater Airy-0).