Martian Clock and Calendar

Copyright © 1997, 1998 by Mickey D. Schmidt, Cadet, USAFA

Here are some notes I have regarding the Martian clock/calendar. We are designing a clock with a custom crystal to keep Mars time and a electronic calendar to mark date and time on Mars. If/When we get time to construct it, it will be a lobby exhibit in our planetarium. It would be nice to have it count down time until the first human arrives on Mars (if we only knew).

Assumptions: A "sol" is a Martian rotation or day/night cycle

Martian year = 668.5968606 sols
Mars Sidereal day = 88642.6632 Earth standard sec long.
Mars Solar day = 88771.7001 Earth standard sec long.

Things we did not include in our considerations. Location of the IAU prime meridian on Mars.

A sample system:

First day of Martian Year occurs on Mars' Vernal Equinox.

Month  days/mo  cum/days
1      28       28
2      28       56
3      28       84
4      28       112      Spring = 194 sols
5      28       140
6      27       167
7      28       195      Spring ends on 27th of 7th month /Summer begins
8      28       223
9      28       251
10     28       279      Summer = 178 sols
11     28       307
12     27       334
13     28       362
14     28       390      Summer ends on 9th of 14th month / Fall begins
15     28       418
16     28       446      Autumn = 143 sols
17     28       474
18     27       501
19     28       529      Fall ends on 13th of 19th month /Winter begins
20     28       557
21     28       585
22     28       613      Winter = 154 sols
23     28       641
24     27       668

Note: Mars year is 668.5968606 sols long therefore we have a need for periodic corrections like "leap year". There is an excess of .4031394 sols each year.

The first fix is to add two days each five years. Even so, there is still an excess of 0.0031394 sols. These added days should be in months with 27 sols.

Every 300 years add an additional day in one of the other 27 sol months. Now there will be a slight deficit of 0.05818 sols. So every 6000 years delete one leap day. Which ought to be good enough for the time being. Even though the deficit is 0.1636 so another leap day could be deleted every 36,000 years. But if anyone is still there by then I'm sure they won't care.

As you can see the Martian year is equal to 24 months of 27 or 28 days in length. A standard time period of 7 days per "week" is used for traditional Earth based religious reasons. The week of only six days eventually ought to be considered vacation periods (if/when vacations for working Martians are a viable option). One of the non-religious days being omitted (during 6 day weeks) probably the last day of the "week".

The year starts on the first day of spring (Northern Hemisphere). Day names on Mars could be the same as those on Earth but I would advise against it. One of the days ought to be reserved as a "holy" day that all faiths use of worship services. Thus reducing the conflict as to which is the "proper" day to worship. Some colonists, may at first want to use the same day that Earth is celebrating or worshiping, but that will soon be out of cycle anyway so to avoid problems one of the days should be set aside for worship for those who chose to do so. This day should not be called "Sunday" perhaps "Holyday" so all religions can assume it is an appropriate day. The other day names based on Roman and Norse Mythology could be used with the exception of Sunday. However - to avoid confusion between Earth and Mars communications new day names ought to be used. (Did Edgar Rice Burroughs' ever include any Barsoomian day names in his books?)

Month names could be January I, January II etc but since these units were derived from Earth lunar cycles and Roman names, these units do not reflect any natural cycles involving Mars moons. New Month names should be invented.

They could reflect a future concept of a terra-formed Mars when there are plants and seasons. I personally like the month names the French tried to impose after the revolution like Blooming, Leafing, Fruiting etc. One could take month names from various cultures around the Earth and apply them to a part of the year which seems a likely match. This practice has been followed for place names on planets and satellites so the precedent has been set.

Other notes:

On the first day of Martian Spring the Sun enters Taurus.

Clock Time keeping during the Martian sol or day:

24 hours is what we are used to but Mars' day is 24 hours and 39 minutes. Three possibilities occur to me.

1. We could use the Earth standard of 86,400 seconds as defining a solar day. Then each "Martian" second will be 1.027450233 seconds. This giving the appearance that each sol is exactly 24 hours long. Thus we could still use the concepts of hours, minutes, and seconds. The would just differ in length by 1.027450233 units. There may be confusion using different time units from Earth but eventually a uniform mean solar time piece for "Martian" business and everyday life will be needed for average colonists. We are used to the concept of a 24 hour day so this looks promising.

2. A metric time of 20 major units each composed of 50 mini units each composed of 100 micro units would yield a day length of 100,000 micro units as opposed to 86400 second per day.

3. The third method would be to keep the second as defined by the International Bureau of Standards but increase the number of seconds per hour so that the day is equal to 1479.58 min/day or 88775.24 seconds per day. This will of course require constant use of leap seconds.

Of the three, the second option would be very useful but I suspect the first option will be chosen because all you need to keep track of time on Mars is a slow clock to keep time.

For coordination between scientific users between Earth and Mars the International defined second would be used for calibrating equipment relating to communications standards etc but for common time on Mars a new second should be adapted.

One might want to adopt a new Year designation such as 2AO for 2 Mars years After Occupation. This might be handy since to use the Earth year designation would require insertion of year designators at unusual and continually differing times.

Time zones on Mars should not be needed for many years so the standard time on Mars would be the either be the time at the designated prime meridian or as I favor the site of first permanent site on Mars.

This is based on my thinking of the subject in 1988 and as amended (see below).

The day lengths of the four seasons are adapted from a paper on the Internet at prior to this information my Mars year had been divided up into three nearly equal trimesters of 28 day months with some 27 day months.