This document is part of the Martian Time Boneyard. It was originally located at http://www3.bc.sympatico.ca/tharsisbooks/Calendar.htm.
Author: Thomas W. Cronin

The simple Mars Calendar and Clock used in the Mars Trilogy novels "Glopry Be To Mars" (Book Three (2005), "Give Us This Mars" (Book Two, 2003) and "As It Is On Mars" (Book One 2001 & 2005).

Last Updated: Feb 04, 2007


Simplest possible Mars Calendar and Clock used in The Mars Trilogy Novels Glory Be To Mars (Book Three, 2005) Give Us This Mars (Book Two, 2003) and As It Is On Mars (Book One, 2001 & Revised Second Edition 2005) by Thomas W. Cronin


Text from Appendix 1 of Give Us This Mars, Book Two of the Mars Trilogy, published March 01, 2003, presented by Tharsis Books.


Mars Clock

Mars rotates on its axis just like Earth, which gives rise to the planetary phenomenon of day and night, which we experience here on Earth too. However, Mars takes a little longer to rotate than Earth, so that a Mars day is a little longer than an Earth day.

One Martian day, or sol, as it is sometimes called, lasts 24 hours, 39 minutes, and 35.238 seconds. A Mars day is thus about 2% longer than an Earth day. This gives Martian clock designers a few problems.

Some people have proposed a new second for use on Mars, about 2% longer than a second on Earth. That way, you could keep the convenience of a 24-hour day on Mars, each hour having sixty minutes, and each minute having sixty seconds, as usual. This is impractical, unfortunately, because the second is a deeply embedded unit in all kinds of engineering and scientific units of measure.

Accordingly, there is no choice but to live with a Martian day almost 40 minutes longer than 24 hours.

A Mars clock or watch will therefore run until 24:39:35 at night, or 12:39:35 at night (close to 12:40), at which instant the time reverts to 0:00 of the next day. Thirty minutes later its is 0:30, or zero thirty in the morning, or half past zero. After another hour, it is 01:30, or one thirty in the morning.

Twelve hours after midnight (at 0:00), it is 12:00 in the morning, but not quite midday. Midday is at almost 12:20, at 12:19:48, to be precise. Nothing unusual happens at this point, and time just increases through the afternoon and evening, until midnight at 24:39:35, when it abruptly reverts again to 0:00, or zero hours.

From all this, it can be seen that a clock or watch must be specially designed for use on Mars, the difference being those nearly 40 minutes just after 24:00 hours, or twelve in the evening.

Days of the week on Mars

The days of the week in the Mars calendar used in the novels have the same names as the days of the week in the Gregorian calendar for Earth, namely Monday, Tuesday, etc.

To start things out, since January 01, 2000 is a Saturday on Earth, and since that day is also Alpha-January 01 on Mars, that day on Mars is designated as a Saturday too.

Now, since Earth local time runs ahead of Mars local time by almost 40 minutes each day, and therefore by a whole day every thirty seven Earth days, on any given date, the day of the week on Earth will not necessarily be the same as that on Mars.

Thus, for example, when it was 4:30 in the afternoon, on Sunday, Alpha-October 14, 1089 (about the time, and the day, of the ESA landing) at the Elbow Plain landing site, it was 6:58 P.M. local (daylight savings) time, on Friday, July 10, 2048, in Washington, D.C.

This is the reason some people have proposed using different names for the days of the week on Mars. The author thinks different day of the week names for Mars are unnecessary and dangerous. You may ask yourself if you would have preferred other names for the days of the week in these novels. The author, for one, would have found that too confusing, and an easy source of error.

The Days and Months of the Martian Calendar

Mars goes around the sun just like Earth, and is similarly inclined on its axis, so we get seasons, just like on Earth. The difference is that it takes Mars almost two Earth years to go around the sun, so that a Mars year is almost twice as long as an Earth year.

To be more exact, one Martian year is 668.599 Martian days. This means we get 23 months in the Martian year, if each of the first 22 months has 29 days, and the last month has 30 days. But that takes care of only 668 days. We have to have a leap day every second year, as well as a leap day every tenth year, to take care of the remaining 0.599 days. The last month is the leap month. To keep things as familiar as possible in the calendar used in the novels, there are two Januaries, two Februaries, and so on, but only one December, as laid out in the table on the next page. Note that each of the four seasons is almost twice as long as the corresponding season on Earth.

Martian Calendar data:

1 Martian year = 668.599 Martian days
1 Martian day or sol = 24 hours, 39 minutes, 35.238 seconds
                        or 1.02749118 Earth days
1 Martian year = 23 Martian months
Saturday, Alpha-Jan 01, 1064 is: Saturday, Jan 01, 2000

Alpha-January: 29 days (Winter)
Beta-January: 29 days (Winter)
Alpha-February: 29 days (Winter)
Beta-February: 29 days (Winter)
Alpha-March: 29 days (Winter)
Beta-March: 29 days (Spring; Equinox: Beta-Mar 04)
Alpha-April: 29 days (Spring)
Beta-April: 29 days (Spring)
Alpha-May: 29 days (Spring)
Beta-May: 29 days (Spring)
Alpha-June: 29 days (Spring)
Beta-June: 29 days (Spring; Summer Solstice: Beta-June 24)
Alpha-July: 29 days (Summer)
Beta-July: 29 days (Summer)
Alpha-August: 29 days (Summer)
Beta-August: 29 days (Summer)
Alpha-September: 29 days (Summer)
Beta-September: 29 days (Summer; Fall Equinox: Beta-Sept 28)
Alpha-October: 29 days (Fall)
Beta-October: 29 days (Fall)
Alpha-November: 29 days (Fall)
Beta-November: 29 days (Fall)
Alpha-December: 30 days (Fall; Winter Solstice: Alpha-Dec 25))
                       (Alpha-December has 31 days in leap years
                       --years ending in either an odd number or zero.)

Martian Thanksgivings (from the novel: As It Is On Mars):

Alpha-April 07, and Beta-October 07

Synchronization with the Gregorian Calendar.

Saturday, Alpha-Jan 01, 1064 is Saturday, Jan 01, 2000.

By a fortuitous orbital coincidence (see below), the Martian calendar on the previous page synchronizes naturally with Earth's Gregorian calendar, so that Saturday, Jan 01, 2000 Gregorian is Saturday, Alpha-Jan 01 in the equivalent Martian year of 1064.

Technically, at 00h:00m:00s Mean Solar Time at zero Martian longitude (on the Airy Meridian), that is, AMST, on Alpha-Jan 01, 1064 it is (to within a second) 20h:40m:32s UST (or GMT) on Dec 31, 1999 on Earth. Midnight at Airy-0 and midnight at Greenwich, at millennium end, are thus 3h, 19m, 28s apart. (Airy Crater is a small crater on Mars, used for the zero of longitude.)

An orbital coincidence occurred in 1999. A Mars winter solstice in the northern hemisphere occurred on Saturday, December 25, 1999. Since Alpha-December 25 is Winter Solstice day in the above Mars calendar, this gives rise to the natural synchronization. Saturday, December 25, 1999 is the same as Saturday, Alpha-December 25, 1063, and hence Saturday, January 01, 2000 corresponds to Saturday, Alpha-January 01, 1064.

Thus the new millennium on Earth begins with the two calendars synchronized, and we may call Jan 01, 2000 synchronization day. (Note that 2000 Earth years corresponds to 1064 Mars years.)

Mars years in the novels

The dramatic events that launch the story in the novel As It Is On Mars all take place in 2038, Gregorian, which is 1084 in the Mars calendar. Mars year 1084 actually begins in 2037 Gregorian, with Monday, Alpha-January 01, 1084 corresponding to Monday, August 13, 2037 Gregorian.

Most of the events in the novel Give Us This Mars take place in the summer of Gregorian 2048, which is the early fall of Mars year 1089, or 25 Mars years and about eighteen Mars months past the Earth millennium of January 01, 2000.

Mars year 1089 can also be written as M25, that is, 25 Mars years past the millennium on Earth, with M corresponding to 1064. Mars year 1064, which begins at the Earth millennium, can be written as M0. Note that if we use the more convenient M-notation for Mars years, leap years are still odd-numbered years, but also years ending in the digit 6 (1070 is M06, 1080 is M16, and so on).


For a Content Summary of the Mars Trilogy, Book One: "As It Is On Mars" and Book two: "Give Us This Mars", and Book Three "Glory Be To Mars", and for Content Summaries of other recent Mars novels, and for links to detailed information about all these Mars novels: See our "Books on Mars" page .