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
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
DAY LENGTH OF MARTIAN CALENDAR MONTHS
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.