A Thought for the Future

William H. Becker
released to the public domain

It is probable that Mars will be the first place where mankind will settle and be permanent residents outside the Earth-Moon system. Can a sensible calendar be adopted for those Mars Citizens?

Fortunately the "Mars Solar Day" (termed a "sol" by astronomers) is quite similar to an Earth Day in time span, being equal to 24 hours, 39 minutes 35 seconds of Earth Time. This should bode well for the pioneer's circadian rhythms. (Mars Sidereal Day is 24 br. 37 min. 22 sec. in Earth time.)

A Mars Year is equal to 686 days 23 hours 52 minutes 32 seconds in Earth Time. Ergo, by calculation, given the 24 hr. 39 min. 35 sec. Sol, a Mars Year works out to have 668.61561 sols (days) in it.

Using a seven-sol week divided into 668.62 sols gives a year of 95 weeks with 3.62 sols left over. Dividing 95 weeks into 5-week months gives a year of 19 months. (Many many different week lengths and number of months were tried but, probably fortunately, the 7-sol week in 19 months works best.)

The 95 seven-sol weeks in 19 months total 665 sol (3.62 sols short of the full Mars Year). The three full sol short can be accounted for by inserting three intercalary sols, not part of the regular week, into the calendar. The .62 of a sol raises the need for a "Leap Year Day". Such a Leap Year Sol inserted as an intercalary sol as needed would be used to account for this fraction of a day in the Mars Year. This Leap Year Sol would have to occur in a little more than 3 out of each 5 years. Leap Years to occur in any year ending in zero or an odd number. Any year ending in 66 would be a Leap Year. Any year ending in 32 in an even numbered century would be a Leap Year. An additional Leap Year will have to be added about every 610 years, on average, to keep calendar in sync with seasons.

In the concept calendar the Intercalary Sols are placed at the start of each yearly quarter. They could be placed elsewhere in the calendar if there were reasons for doing so. The yearly quarters on Mars do not correspond to the seasons due to the eccentricity of the Mars Orbit. Seasons are not of equal length.

The concept Mars Calendar bears a good deal of similarity to the proposed 13-month "Cosmic Calendar" advocated for Earth use. This similarity adds weight to the proposal for adoption of the "Cosmic Calendar" for use on our planet.

The concept Mars Calendar is "perpetual", i.e. it is the same every year except for the presence or absence of Horos Sol (Leap Year Day). Thus no "grasshopper dates" as in our Gregorian Calendar. (Also, of course, there is no "grasshopper date" problem in the Cosmic Calendar.)

The Mars Calendar cannot be translated to any Earth calendar (day for day) due to the different Solar Tears of the two planets. The calendars proposed are primarily for local (planet) use.

If both Earth and Mars calendars are considered to have started at the same zero point, then any Mars Year number will be .5316514 times the Earth Year. Thus Earth Year 2001 would see the start of Mars Year 1064 at its Northern Hemisphere Winter Solstice (if that point established as Mars New Year's Day). Likewise, any Mars Year multiplied by 1.8809316 will give approximate Earth Year number. (Ergo: 1064 x 1 .8809316 = 2001.3112) or (2001 x .5316514 = 1063.8345)

Notes on the Mars Calendar

X = Intercalary Sol. Use "Sol Name" only. No date number other than Year. "Horos Sol" occurs in Leap Years only, i.e., approx 3 out of 5 years. Other Intercalary Sols (Mars, Phobos, Deimos) occur every year. Intercalary Sols mark start of Year's Quarters. There are 167 Sols (days) in first, second, and fourth quarters (including Intercalary Sols). There are 168 sols in non-Leap Years (no Horos Sol occurring). Mars Sol (New Year's Day) equals Mars Winter Solstice in Northern Hemisphere.