Rationale for the Martian Calendarís Structure

by Bill Hollon
© 1998 by Leonard Bromberg
edited by Thomas Gangale

Calendars on Earth have long been an indispensable part of everyday life. They indicate when to expect a change in seasons; they suggest to the farmer when to plow and plant; they tell priests when it's time to prepare for fasts or festivals; they help everyone plan for the future.

Some of those reasons for the need of calendars on Earth are critical to the purposes of mankind on Mars. Seasonal changes on the red planet are much more severe than on Earth. By comparing Gregorian and Martian Calendars, explorers and settlers can celebrate special days, whether civil or ceremonial, at the same time as they are being observed on the home planet. Planning for the future is extremely critical for Martian endeavors in order to ensure that needed provisions will be on hand in a timely manner.

Because features of the Martian Calendar match those of the Gregorian, it is easy to compare time intervals between the two planets. One way this similarity has been provided is that we use the same words for generic units of Martian Age time measurement as we do for comparable earthly periods. We speak of a Martian year, quarter, month, week and day rather than using terminology that is unique to Mars. Also, days on both planets are divided into hours, minutes and seconds. Many of these time periods are further divided into the same number of parts on both Earth and Mars. Their actual lengths, of course, are not identical.

Another aid to understanding correspondence between the two calendars is because they are formed with the same structure. A red planet day is very close in length to Earth's day. Therefore, the seven-day Mars week is very close in length to a terrestrial week. But both the beginning and extent of these short-term periods is different because the two planet's natural days are not synchronized.

One of the Gregorian Calendar's most rational features is its division of the year into twelve months. Because the number of months totals twelve, a Gregorian year can be divided into two halves of six months and/or four quarters of three months each for planning purposes.

A natural year on Mars is almost twice the length of one on Earth. Therefore, a twelve-month Martian calendar would have resulted in month lengths of almost twice as many days as calendars have on Earth. This would have made comparisons between terrestrial and Martian months misleading at best.

An easy resolution of this problem resulted from assigning 24 months to the Martian calendar, giving them lengths of mostly 28 days --- very comparable to months on Earth. Further, this 24-month calendar lends itself to division into equal periods of not only halves and quarters, but also eighths. Incidentally, an eighth of the Martian calendar is very close in elapsed time to an Earth year's quarter.

Martian Calendar years are kept in synchronization with nature simply by beginning each new calendar year on the day of the vernal equinox, regardless of how early or late its hour might be. Most Martian Calendar years have 669 days but others have 668.

Because a prior year's length is terminated at the start of a new solar year, leap year rules are not required. For all practical purposes, the length of any Martian Calendar year, either past or future, can be calculated from Mar's year length and the day and time of any recent Martian vernal equinox.

To prevent confusion between various expressions of what might be either a terrestrial or Martian Calendar date, names for specific Martian days and months as well as numbers for their years are different from those used on Earth. However, days of the Martian week are named after solar system members just as they are on the home planet.

Martian days were named with these heavenly objects in mind: Sun, Phobos, Deimos, Earth, Venus, Jupiter and Saturn. Actual names of most of the seven are borrowed from roots of these object's names in various languages (and combined with the English suffix "day.") These names are not likely to be confused with those of an Earth day.

Month's were named to honor individuals who either participated in early space exploration or who contributed to mankind's understanding of science. Two of the 26 alphabet letters had to be omitted, as were names of many individuals who deserved to be remembered this way.

Martian months are named in alpha sequence from Aldrin thru Zubrin as an aid for those who might find it difficult remembering the order of all 24 months. A fairly good idea of each month's location in the year can be had by envisioning where the first letter of its name fits within the alphabet.

Listed in the accompanying chart is the length in days of all Martian Calendar months. The chart is not intended to serve as a calendar, but rather illustrates lengths of major subdivisions of the year. Sixty percent of calendar years have month lengths as shown. Of the other forty percent, the only difference from values given is that their year ends after the 27th day of the 24th month.

DAY LENGTH OF MARTIAN CALENDAR MONTHS

First Quarter Second Quarter Third Quarter Fourth Quarter
Month
Number
Nbr.
Days
Month
Number
Nbr.
Days
Month
Number
Nbr.
Days
Month
Number
Nbr.
Days
128 7 28 1328 19 28
228 8 28 1428 20 28
328 9 28 1528 21 28
428 10 28 1628 22 28
528 11 28 1728 23 28
627 12 27 1827 24 28


Note that the length of all major divisions of the Martian Calendar year, including the month, eighth, quarter and half, are either identical to, or within a day of, that of any other comparable time period. This congruence is critical to the use of accumulated Martian statistics for planning future red planet activities.