Thursday, December 06, 2007

Months on Mars

I was looking at the Mars Rovers page the other day and came across this classroom activity:

Mars Calendar Project

Learning Goals: Students will learn how time is measured on Mars by creating a Martian calendar.
Overview: Students are grouped and given ideas on how the Martian calendar would differ from that of Earth’s.

  1. Mars rotates slightly slower than Earth — one Mars solar day, or sol, equals 24.6 hours or 24 hours, 40 minutes.
  2. Mars orbits the Sun in 687 Earth days or 670 Mars sols.
  3. Mars’ rotational axis tilts towards the Sun at an angle of 25 degrees. Earth has a similar tilt of 23.5 degrees. This tilt causes the seasons on both planets.
  4. Mars has two moons. Phobos travels around the planet 3 times in one sol. Deimos travels around Mars once every 30.3 hours.

From this information, the groups will design a Martian calendar.

It is important to take into account such questions as:
• Will you use days, weeks, months?
• What makes a month a month on Mars?
• What will you call a month?
• Will there be a leap year? If so, when will it fall?
• What about Earth holidays? Mars holidays?
• When will the calendar begin (i.e., when is year “0”)?

I was interested in whether I could use it sometime although I do not teach science classes (it's not really just a science question anyway) so I was saving a copy of it and decided I should try it before I consider asking someone else to try it. I got a little obsessed with it then for a while and this is what I came up with. I'm sure there are some other Mars calendars out there somewhere but this is my first impression. It's a little sketchy. FWIW.


Sols are divided into 24 Martian hours or “horas” of 60 Martian minutes or “minuta” of 60 Martian seconds “secunda?” each. The units of time will be given slightly different names to distinguish Earth time units from Martian ones. It is based on the close similarity of the Martian sol to the Earth day. This makes people feel more comfortable. Each minute is just 1.6 seconds longer, each hour only 1.6 minutes longer, so we just feel it is a little off from Earth. Digital watches need to have a "Mars" setting.

Weeks are of seven days, in keeping with Earth traditions. These will become out of synch with Earth days. To keep the difference to Earth clear, they could be called Sunsol, Mercsol, Venussol, Earthsol, Marssol, Jupitersol, and Saturnsol. this celebrates the sun and 6 inner planets, renews a tradition, and keeps Sunsol and Satursol as familiar anchors at the week’s ends.


There will be 10 months of 67 days each. These will not be called months since they are not based on the moon. They should be called "deciannums" or something like that. Perhaps decigaod? (from the Russian word for “Year”) would do.

The months will be named for the Russian numerals 1 through 10 in honor of Russian attempts to explore the red planet: adeen, dvah, tree, chetyreh, pyat, shest, sem, vosem, devyat, desyat. Or maybe not. Whatever. They need tweaking so maybe we can just take the first three letters or so. Dates will be expressed either as the day of the year as if a fraction as in Sol 167/670, or with the month system. The expression “01-09-62-Sunsol” would mean Year One, Deciannum 9, Sol 62, a Sunsol, easily converted and recognizable as the 665th day of the Martian year ((9x67)+62).

Although it creates a long month, base 10 is handy and it creates 10 months of equal length, as opposed to the possible (nightmare) alternative of 20 months of different lengths (33 and 34 days). Since there is no moon, months have no real reference. Also, it would be hard to even name and remember the names of 20 months. Many things are kept the same, but this is one difference people would have to adjust to (different months, longer seasons, a longer year). For the more "everyday" units of time of up to a week, the Earth traditions are (nearly) followed.

That means every 67-sol month will have 9 weeks plus 4 sols (that final week having at least 2 holidays).

The year will begin on the day of the winter solstice in the northern hemisphere. The first day of the sixth month will therefore be the day of the summer solstice in the northern hemisphere. Solstices and equinoxes will be holidays. Spring equinox would fall near 3/33 (the 33rd day of the 3rd month, and autumn equinox near 8/33).

The 66th day of each month will be a day of celebration, and the 67th day a day of quiet reflection on the past deciannum (or whatever it is called).

Saturnsols and Sunsols may be holidays as on Earth. However, people may have their own days off and develop their individual holiday patterns, partly because of the demands of rotational scheduling.

People will maintain an awareness of the Earth calendar and celebrate many holidays of Earth, the home planet, synchronously.

The day of closest approach to Earth will be celebrated with many activities and exchanges of messages with Earth and celebrations of Earth cultural heritage.

The days when Earth is behind the sun and out of contact will also be some kind of a holiday since communication with Earth is not possible (or difficult, at least until a network of sun-orbiting communication satellites are established); at this time it is important to commun(icat)e well with one’s local fellows. Local Martian cultural heritage, autonomy, and unity is celebrated on these days.

There will be a similar festival for the closest approach to Mars’ other neighbor, Jupiter, which shall be celebrated by Jupiter-viewing parties.

Local meteor showers and other annual celestial events will be celebrated -- probably by tunneling deep underground-- but also perhaps by viewing parties.

Year One will be the first year of human landing and living on Mars.

Events such as the date of the first human birth on Mars, and the date of the first human death on Mars, will become holidays.

Mars, like Earth, will have 24 time zones, based on a yet-undetermined Greenwich point which would probably be the first long-term human settlement.

Not much attention will be paid to Phobos and Deimos in the design of a calendar as they are quite unlike Earth’s moon.

Leap years would be added if the moment of the winter solstice were not going to fall on the first sol of the year. A day would be inserted or removed from the 10th deciannum (decigaod?) as needed.
Afterthoughts: OK, now I've googled around. I realize my 7-sol week makes a non-perpetual calendar, but I like it that way. There needs to be some chaos. However, some other good ideas were to use a 24-month calendar of 28 sols, with leap year day variations in the final month. Two justifications for hanging onto a 28-day month are that the Earth and its moon may be visible, and the human menstrual cycle. Twenty-four also echoes the 24-hour day. It is also familiar, and the Martian year can be divided into two earthlike years. For example, the year could begin with Janearly, Febearly, and Marley, while the 13th, 14th, and 15th months could be called Janulate, Feblate, and Marlate. I would suggest getting rid of the broken ruins of Latin Roman months like Sept, Oct, Nov and Dec unless they mean 7, 8, 9, and 10 again.

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