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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.
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|
|Zungo||27 (or 28 if in leap orbit)|
The month names are based on Frans Blok's Rotterdam System.
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
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|
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
999. Or it may be shown in 3-digit millisol format with 3 decimal points. e.g. from
Therefore, after putting the date and the time together with a colon separator in between, you will see
As you may have guessed, the Martian timestamp is in the format of
In future, we will incorporate a time zone system similar to this one proposed by Ares Astronautics.