Davidian Martian Calendar

The Davidian Martian Calendar is a proposed system of time-keeping designed to serve the needs of future human settlers on the planet Mars. It was established by David Powell in Gregorian Year 1988. In 1996, a system of converting dates between Gregorian and Davidian calendars was created.

Calendar Terms
The Davidian calendar uses the same terminology as that used by the Gregorian calendar:

Minute: Period of 60 Martian seconds (61.62s on Earth).

Hour: Period of 60 Martian minutes (61m 38.968s on Earth).

Day: Period of 24 Martian hours (24h 39m 35.244s on Earth).

Week: A period of 10 days.

Month: A unit of time that on Mars simply means 1/12 of a year.

Year length and intercalation
The Martian year is 669.5907 Martian days long. Therefore, with very rare exceptions, every century must have 59 leap years. That means that unlike on Earth, leap years are actually more common than "common" years.

Leap years are as follows:


 * Every even numbered year except for those that end in "00"
 * Every odd-numbered year that is evenly divisible by 5: 05, 15, 25, 35, 45, 55, 65, 75, 85, 95

Additionally, years that end in 0000, 2000, 4000, 5000, 6000, 8000, and 9000 begin with a January 0 or "Millennium Day" that does not belong to any day of the week.

Calendar Layout
The year is divided into 12 months. The months of January through June have 50 days, while July through December have 60 days. In addition, two holiday weeks of 4 or 5 days at the end of June and 5 days at the end of December is added to equal 669 or 670 days, depending on leap year. This keeps the calendar perpetual.

There are ten days per week, named after astronomical phenomena as seen from Mars, to follow the tradition of the Earth Gregorian calendar: Sunday, Phoboday, Deimoday, Wednesday, Thursday, Friday, Saturday, Uranuday, Neptday, and Teraday.

June 55th is an intercalary day that only occurs during leap years.

Epoch
To simplify the equation necessary to convert Gregorian dates to Martian dates, a common epoch is needed. Originally, the Gregorian epoch (January 1, 0001 CE) was used. However, it was later decided that the Davidian calendar would follow the same epoch as the Holocene calendar, with a minor adjustment to keep Martian seasons occuring during the same months as Earth seasons, as well as to ensure that Earth year 2000 is Martian year 6400. This means that January 1, 0000 on the Davidian calendar is equivalent to January 1, 10037 BCE of the Gregorian calendar. This means that every date in recorded history is expressed in positive-numbered years.

Calendar dates use the suffix DM, to distinguish them from BCE/BC and CE/AD (Gregorian) and HE (Holocene). For dates that occurred before the epoch, negative numbers are used. For example, 20000 years before Year 0 would be expressed as -20000 DM.

Start of the year and Seasons
The solstices and equinoxes occur on the following dates:

Rationale
While other Martian calendars incorporate very creative things like new names for months, days of the week, etc, the Davidian Calendar builds from what is already familiar to future settlers. The term "sol" is not used. A "sol" is defined as the time between two successive noons or midnights. A "day" is more loosely defined as a period that roughly conforms to the human circadian cycle. Only on Earth and Mars are a "day" and a "sol" the same thing. On other planets, a "sol" is much longer or shorter than a "day". Therefore, the distinction is necessary and the term "day" is used in all Davidian calendars.

A 10-day week is used, rather than a 7-day week. This is because a 10-day week makes more sense. A week that is divided between 5 working days and 5 leisure or "weekend" days promotes a healthy life-work balance, and eliminates the need for holidays. Having half of the work force work the first half of the week and the other half working the second half of the week reduces the unemployment rate. The only reason why Earth calendars cling to a 7-day week is because of religious objections over the sabbath. It is anticipated that Martian settlement will occur at a time when religion is no longer as dominant in advanced civilization.

Conversion
The Davidian Calendar is unique among proposed Martian calendars in that it is designed to be converted back and forth between Davidian and Gregorian dates.

Gregorian to Davidian
The formula for converting Gregorian (Earth) dates to Davidian (Martian) dates:

( (ED + 10037) * 365.26 ) / 686.98
 * Where "ED" = Earth Date

For example:

July 20, 1969 (1969.5479) is equivalent to October 21, 6383 (6383.7545).

( (1969.5479 + 10037) X 365.26) / 686.98 = 6383.7545

Davidian to Gregorian
The formula for converting Davidian (Martian) dates to Gregorian (Earth) dates:

( (MD X 686.98) / 365.26) - 10000
 * Where "MD" = Martian Date

For example:

December 2, 6365 (6365.9178) is equivalent to January 1, 1973 (1973.0006)

( (6365.9178 X 686.98) / 365.26) - 10000 = 1973.0006

Historical Events
Major world historical events, shown in Davidian, Gregorian, and Holocene dates. Note: approximate "circa" dates are rounded and do not calculate directly.

Holidays
Holidays present a dilemma in a multi-planetary civilization. Holidays that celebrate significant historical events will probably be celebrated once per Martian year on the same date each year. Holidays of religious significance, such as Christmas, Easter, Passover, and Ramadan will probably be celebrated when they occur on Earth, regardless of what the date happens to be on Mars. This means they will occur twice annually in varying months and seasons.


 * Easter on Mars presumably occurs on the Martian Sunday closest to the Earth Sunday it is observed on Earth, rather than on the actual calendar date.