The “12×56/270” Mars calendar

Since these data are useful especially for future in situ human exploration, and several meteorological phenomena are local time/sol dependent in many respect, I used a calendar that is more practical in the everyday sense of time: the Mars year in the diagrams is split to 668/669 sols (instead of continuous Ls values) and 12 equal-interval (56 sol) months (Month 12 is 52/53 sols long). Although many Mars calendar proposals exists, for handling such climatic data, an equal-length larger unit (“month”) and sol-based calendar fits the best.

For better comparison to traditional climate diagrams, the starting point of this calendar is set to the 1st sol after the northern winter solstice (Ls 270, “January”) (also close to perihelion at 251 Ls). (Not as in Ls=0-starting calendars which start the Mars Year in “April”, like the [1], or [here]).

Also, Ls-based calendars obscure some natural phenomena (real length of summer/winter in northern/southern hemisphere).

The Ls=0 (spring) starting calendar is close to the one used by ancient Romans, where winter did not count since there was no main activity at the fields. Some Mars calendars like the CMEX Mars Calendar use variable-sol (40-72) -long months depending on the actual solar distance.

Comments. For practical purpose (like “monthly” measurements) I used equal-sols months. Variable-length time units also go back to antiquity when the length of the hours of a day depended on the length of the period from Sunrise to Sunset; the total time was then divided. For practical purposes I keep each time unit (sol, week [not used here] month, year) equal length (as much as possible).
We kept traditional names of days/months, because these names are stronger than civilizations: although it may be a proble not to mix them with Earth Dates. We also kept AD years since there is no accepted first year for Mars (may be only after human landing). The first human missions will probably not use such calendrat: they will count sols from the arrival/to the departure. Jan 1 is always monday, so the last days of the year will have a jump in the traditional neverending row of names of days.

Here is an example of the use of calendar for 2007-8-9.

Main points of the year used for creating the diagrams
*1st sol of the Year (1999/12/25) **1st sol of the next Year (2001/11/12)

Ls   Orbit (Vanilla) Orbit ("real")  Spacecraft Clock Description
269.5    3558        5241            ~630529096        *
270     11961        13644           ~689871962        **

Main data of the “12×56/270” calendar used
A    B sol C Ls D clock    E Ls  F sol Comment
1    1    269.5 630529096  34.5  56    Ls 269,5 =?sol 1 =?Northern Winter Solstice
2   57    305.5 635496738  31.5  56
3  113    337.5 641171890  28.5  56    Ls 0 =?sol 153 =?N.?Spring Equinox
4  169      7.5 645758026  26    56
5  225     34.0 650213502  25.5  56
6  281     60.0 655689924  24.5  56    Ls 71 = sol 305 aphelion (249 m km)
7  337     85.0 660194188  25.5  56    Ls 90 = sol 347 =?N.?Summer Solstice
8  393    111.0 666916360  26.5  56
9  449    138.0 670405188  29.5  56
10 505    168.0 676122612  32    56    Ls 180 = sol 525 =?N. Autumn Equinox
11 561    200.5 680496118  35    56
12 617    236.0 685294644  33    52/53 Ls 251 = sol 639 perihelion (205 m km)
–    1    269.5 689871962              (668+1 sol)

Key
A: Month number;
B: 1st sol of the month (sol of the year)
C: Corresponding Ls (approx.);
D: Corresponding MGS Spacecraft Clock No. for 1999-2001 ;
E: Length in Ls unit;
F: Length in sols.
 

References:
[1] Clancy et al., Journal of Geophys. Res 105, p 9553, 2000