This document is part of the Martian Time Boneyard. It was originally located at
Author: Linda Naughton and Robert O'Meara

Wordsmyth Games - Martian Dreams Time System
Wordsmyth Games

Martian Dreams Time System

by Linda Naughton and Robert O'Meara

In creating the theme for our original sci-fi game Martian Dreams, we were presented with the challenge of deciding what kind of time system to use. Timekeeping in modern culture - seconds, minutes, hours, days, weeks, months, years - is all grounded in the rotational period of the Earth and Earth's passage around the sun. Because the lengths of the days and years are different on Mars it is impractical to have a single time and calendar system for both planets. It would be like living without time zones on Earth. Sure, you could synchronize everything so that it was 12noon in both New York and Tokyo at the same time, but then the Japanese would be eating lunch (at noon) when it was pitch black outside and going to sleep (at 10pm) just as the sun was coming up.

Throughout the years, hundreds of time systems have been proposed for keeping track of time on Mars. The Martian Time Web Site catalogs many of these systems and the history behind them. This site provided much of the research material we used in creating the Martian Dreams time system.

It is important to note that the Martian Dreams system was designed for a role-playing game. Though we tried to keep it as realistic as practical, it was not intended as a completely scientific undertaking.

The Day

The Martian solar day is 24 hours, 39 minutes, and 35.2 seconds long. To avoid confusion between Earth solar days and Martian solar days, a convention was adopted early on at NASA to refer to Martian solar days as "sols". We kept that convention in our system.

It would be possible to divide a sol into hours/minutes/seconds like on Earth, but those time units would have to be longer on Mars. We believed this would cause endless confusion. If someone said "I'll meet you in ten minutes" - you wouldn't know if they meant Earth minutes or Martian minutes. Keeping track of units in scientific and technology applications is hard enough without having to worry about whether the author of a document meant "meters per Earth second" or "meters per Martian second".

Though there are several ways around this problem, we decided it would be better to use a time system without hours/minutes/seconds at all. This would require an adjustment period by new colonists from Earth, but would be easy enough to use once you got used to it.

The Martian Time website contained several decimal clock systems. One in particular appealed to us - a decimal clock created by Shaun Moss for Virtual Mars. This clock divided the sol into 1000 millisols, which we term "mils". Each mil is approximately 88 seconds long. Instead of measuring time in hours/minutes/seconds, it is measured in the number of mils that have passed since the beginning of the day.

Since a mil is roughly a minute and a half, new colonists should be able to make the transition fairly quickly. If someone says 20 mils, you multiply by 1.5 and you know they mean 30 minutes. There is no equivalent to seconds in this system, although fractional mils can be used when needed.

The clock goes from 000.000 to 999.999 before wrapping around. You can read the times as straight numbers, just like military/24-hour times: 500.000 would be "five-hundred" and 245.237 would be "two-forty-five". The decimal number is often dropped, just as seconds are dropped when people on Earth read 3:15 and ten seconds as "three-fifteen".

There would doubless be timezones on Mars just as there are on Earth. That way 0500 would mark the middle of the day everywhere, and not afternoon in Tharsis and mid-morning in Syrtis Major. We didn't really delve into the timezones, other than to identify that they exist.

We've recently become aware of a different clock system, commonly referred to as the "timeslip" clock, that uses the same length hours/minutes/seconds as Earth. On Earth, the 24-hour (military) clock goes from 00:00:00 to 23:59:59 and then wraps around again. The Martian equivalent would go from 00:00:00 to 24:39:35 before wrapping around. It's unusual in that the last "hour" in the day has only 39 minutes, but otherwise is equivalent to the Earth system. This seems like a better all-around solution because it keeps hours/minutes/seconds the same and avoids having to come up with new terms like "mil".

The Week

Since the week is such an important facet of everyday life in our culture, we felt it was vital to keep the concept alive in our Martian time system. We chose a 7-sol week, just like on Earth. Only the names are different.

In choosing the names, we went back to the historical origin of the weekday names on Earth. They can all be traced (as far as modern research can suggest, anyway) back to the names of the planetary bodies visible to ancient cultures.

  • Sunday - The Sun
  • Monday - The Moon
  • Tuesday - Mars
  • Wednesday - Mercury
  • Thursday - Jupiter
  • Friday - Venus
  • Saturday - Saturn

We kept the same planetary associations behind the names chosen for our Martian weekdays, and just used other names (Latin, mostly, but we changed Aris to Ares for Tuesday because, well, it looked cooler). Also the "day" part of each name was replaced with "sol" to give us:

  • Sol Solis
  • Sol Lunae
  • Sol Ares
  • Sol Mercurii
  • Sol Jovis
  • Sol Veneris
  • Sol Saturni

We figure that the "Sol" prefix would most often be dropped in everyday use, and people would say "See you next Jovis" rather than "See you next Sol Jovis". Tacking "sol" onto the end would make the names a bit unwieldy; Mercuriisol doesn't exactly roll off the tongue.

It is useful to note that there is no link between the day of the week on Earth and the sol of the week on Mars - Sol Lunae is the second day in the Mars week, but that doesn't mean that it's Tuesday back on Earth.

Thomas Gangale has made a convincing argument in favor of naming Tuesday "Sol Martis" instead of "Sol Ares". Although Ares is commonly known as the Greek version of Mars, Martis is the true Latin name for Mars.

The Month

It takes Mars about twice as long as Earth does to orbit the sun (about 687 Earth days, or 669 Martian sols). It is useful to break up this orbital year into months and seasons, just like on Earth. The calendar system we chose for our months is a variation on the system used in the Darian Calendar, created by Thomas Gangale.

The Martian year in the Darian Calendar (and ours) is divided into 24 months. Most months have 28 sols, but every sixth month has only 27. Leap years add an extra day to the last short month of the year, bringing it to 28 instead of 27.

One additional convention adopted from the Darian Calendar is the idea that the first of the month always begins a new week. In other words, the 1st, 8th, 15th and 22nd days of every month are always Sol Solis. The 2nd, 9th, 16th and 23rd days of every month are Sol Lunae.

During the Martian year, there are seasons just like on Earth. The months are linked to the seasons. Just like an Earther instinctively knows that July is in the middle of the summer in America, a Martian similarly knows that Sagittarius is the beginning of autumn in the Hellas Basin.

The major change from the Darian Calendar is the names of the months. Our months are named after constellations. We chose them by taking each Earth month and picking two constellations that have their peak visibility during that month. Ideally, we would have chosen among constellations that had their peak visibility on Marsduring a particular time of year, but we couldn't find any info on that. We had to settle for the peak visibility on Earth. Our research led us to a List of Constellations By Month, written by Chris Dolan. Our choices from that list were fairly arbitrary, based on length, pronunciation, and general aesthetics. For example, our August choices were Sagittarius and Lyra.

We did make two minor changes to the names, however. Capricornus became Capricorn (after the Zodiac sign, which we felt was more familiar than the longer constellation name), and Ursa Major and Ursa Minor were combined into a single month of Ursa.

Our month names are:

  • (Southern Autumn)
  • (Southern Winter)
  • (Southern Spring)
  • (Southern Summer)

The Year

Although the year, scientifically, is based upon the travel of the Earth around the sun, there is also cultural significance to this measurement. Age in years connotes maturity and development - if someone is "20 years old" there is certain cultural significance to that figure. Years are also important in celebrating holidays, anniversaries, and other yearly events.

We felt that the cultural significance of years was the most important factor for our time system. We decided to align our Martian calendar with Earth years. The year in the Martian calendar is determined by the year on Earth in Greenwich. Thus, a sample Martian date might be Sol Ares, 3 Aquarius, 2001. Holidays, birthdays, etc. are all celebrated on Mars in synch with the celebrations in Greenwich.

This decision makes tracking the year very easy. You don't have to establish the start of a Martian "epoch", or wonder whether someone means Martian years or Earth years when they say "I'm 20 years old". In short, it's one less thing to worry about when converting between Martian time and Earth time.

There are, of course, drawbacks to such a system. There's no direct link between the Martian month and the year number. Part of Sagittarius may fall into 2001 and the rest into 2002. Christmas in Greenwich might begin in the middle of the afternoon on Mars. There's also no link between the year and the seasons on Mars - 2001 might contain Fall and Winter and 2002 Spring and Summer.

On the whole, though, it seemed a lot less confusing than keeping track of two completely independent year systems.


No matter what time system Martian colonists end up using, it's unlikely they'll ever escape the system they left behind. As long as communications, business dealings, transportation, etc. continue between Earth and Mars, it will be important to know the time on both ends. Our guiding principle in creating this system was to come up with something that would make sense for everyday life on Mars, but still be reasonably familiar to Earth residents and new colonists. That way, a businessman in London can understand the answer to "What time is it on Mars?" and avoid waking up the CEO of Ares Technologies in the middle of the night with a phone call.