Mars Calendar

manny kung edited this page Dec 31, 2018 · 18 revisions

Mars Calendar

Revised : 31 Dec 2018

Timekeeping on Mars

We have come a long way from having ambitions to send humans to Mars. In preparing for humanity to one day settling on Mars and begins a whole new way of life, it is conceivable that a brand new calendar be created to cope with the change of time and seasons for this unique planet. Discussions on how to keep track of time on Mars are numerous on the internet.

One basic question is that what day and time on Earth a future colonist should declare as the year 0 on Mars.

While the Planetary Society's Mars' Calendar considers April 11, 1955 as the prime candidate, Shaun Moss of the Mars Society and Peter Kokh of the Moon Society proposed that "March 12, 1609" be the most fitting one.

The advantage of this particular earth date was that it coincided with the areocentric solar longitude (Ls) at zero degree, i.e. Ls=0°. It also bore the testament of the beginning of humankind's first love affairs with Mars with the invention of Galileo's telescope and his scientific observations circa 1609.

This is a convenient designation since Ls does a good job of defining the seasons of Mars. From the point of view of the northern hemisphere, Ls is 0° at the vernal equinox (beginning of northern spring), 90° at summer solstice, 180° at autumnal equinox, and 270° at winter solstice.

Design of the Mars Calendar

The Martian calendar used in mars-sim is a variant form of the Utopian Calendar for the Mars Society. It was based on Tom Gangale/Frans Blok's Darian Calendar.

A day on Mars is called sol. One Martian year is referred to as an orbit. It is 668.5921 Martian sols long.

In mars-sim, an standard orbit has 668 sols. If it is a leap orbit, it has 669 sols.

A leap orbit must satisfy the following 3 conditions at the same time :

(1). divisible by 10, (2). NOT divisible by 100, (3). divisible by 500.

Martian Month

An orbit has 24 months with either 27 or 28 Sols.

A standard month has 28 sols.

If the month number is divisible by 6, that month has 27 sols.

If that year is leap orbit and the month number is 24, that month has 28 sols.

Month Name # of Sols
Adir 28
Bora 28
Coan 28
Deti 28
Edal 28
Flo 27
Geor 28
Heliba 28
Idanon 28
Jowani 28
Kireal 28
Larno 27
Medior 28
Neturima 28
Ozulikan 28
Pasurabi 28
Rudiakel 28
Safundo 27
Tiunor 28
Ulasja 28
Vadeun 28
Wakumi 28
Xetual 28
Zungo 27 (or 28 if in leap orbit)

The month names are based on Frans Blok's Rotterdam System.

Martian Week

There are seven sols in a Martian week with the following week names:


Every Martian month has 4 weeks. On months with 27 sols, the last week only has 6 sols and Jovisol is clipped.

This allows the first sol of every month and every orbit to be Heliosol.


The time of the day, i.e. a sol, is loosely based on Bruce Mackenzie's Metric Time for Mars.

One may break down the metric time in a sol into the following common units:

Units Fraction of a Sol Earth Time
decasol 1/10 2.46 hours
centisol 1/100 14.8 minutes
millisol 1/1000 1.48 minutes

mars-sim, however, adopts only the millisol as the unit of keeping track of time in a sol.

It's either in 3-digit millisol format without the decimals, e.g. from 000 to 999. Or it may be shown in 3-digit millisol format with 3 decimal points. e.g. from 000.000 to 999.999.

Therefore, after putting the date and the time together with a colon separator in between, you will see 0017-Adir-03:523.234.

As you may have guessed, the Martian timestamp is in the format of orbit-month-sol:millisols.

In future, we will incorporate a time zone system similar to this one proposed by Ares Astronautics.

You can’t perform that action at this time.
You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session.
Press h to open a hovercard with more details.