The Architecture of Time, Part 2: The Darian System for Mars 2006-01-2249
The Darian calendar is a complete timekeeping system for the 24-hour, 39-minute, 35.244-second sol and the 668.5907-sol vernal equinox year on Mars. Features include:
24 months, normally containing 28 sols, with three to four 27-sol months spaced regularly throughout the year to total either 668 or 669 sols. This results in a month whose length is within 6 percent of the mean Gregorian calendar month, within 3 percent of the lunar month, and near the statistical mean of the human menstrual cycle.
A nominal seven-sol week, with six-sol weeks ending the 27-sol months, thus allowing every month to begin on the first sol of the week. The numerical sol of any month always occurs on the same sol of the week.
Since the new year always begins on the first sol of the week, there are only two types of calendar years: one common year and one bissextile or “leap” year. This is in marked contrast to Earth's Gregorian calendar, which actually comprises 14 different types of calendar years, one beginning on each of the seven days of the week for common years and leap years.
The calendar year begins on the vernal equinox, a standard astronomical reference point.
A set of intercalation formulas keep the calendar synchronized with the vernal equinox for up to 10,000 Martian years as the length of the Martian year increases.
A defined epoch allows the Darian date and local time on Mars to be calibrated with the Gregorian date and local time on Earth. The defined epoch allows all historical telescopic observations of Mars to be expressed in non-negative Martian dates.
Calibration tables showing equivalent dates and times in Earth and Mars for equinoxes, solstices, and perihelions from 1874 to 2127, and oppositions and conjunctions of Mars from 1610 to 2099, are provided. Intercalation precision and annual perturbations are discussed, as well as the solar equation of time throughout the year.