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
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.