Revised : 13 Sep 2024

We have come a long way from observing mars to 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 when living in this unique planet.

Interestingly, 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 would define as the Year 0 (or Orbit 1) on Mars.

While the Planetary Society's Mars Calendar considered April 11, 1955 as the prime candidate, Shaun Moss of the Mars Society and Peter Kokh of the Moon Society proposed March 12, 1609 be the most fitting date to begin counting. This epoch (at 12 March 1609, 19:06:20 UTC) is called the Telescopic Epoch.

On this particular date of 1609, the areocentric solar longitude (Ls) was at zero degree, i.e. Ls = 0°. Incidentally, the invention of Galileo's telescope and his scientific observations on Jupiter and Mars also began circa 1609 and bore the testament of the beginning of humankind's first love affairs with Mars.

Ls is indeed a convenient designation that does a perfect 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). It's 90° at summer solstice; 180° at autumnal equinox, and 270° at winter solstice.

In mars-sim, we settle with designating 2028-08-17 15:23:13.740 UTC as our epoch time from Earth's perspective, that is the beginning of each simulation session (starting as Sol 1 Orbit 1). Essentially, we use the formulae from Goddard's Mars24 Sunclock — Time on Mars site to numerically back compute the exact Earth time that would result in having a value of Mars Ls as closest to zero as possible.

Earth	Mars
Year	Orbit
Month	Month
Week	WeekSol
Day	Sol
Hour	[Decasol]*
Minute	[Centisol]*
Second	[Millisol]**

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. One orbit 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
1	Adir	28
2	Bora	28
3	Coan	28
4	Deti	28
5	Edal	28
6	Flo	27
7	Geor	28
8	Heliba	28
9	Idanon	28
10	Jowani	28
11	Kireal	28
12	Larno	27
13	Medior	28
14	Neturima	28
15	Ozulikan	28
16	Pasurabi	28
17	Rudiakel	28
18	Safundo	27
19	Tiunor	28
20	Ulasja	28
21	Vadeun	28
22	Wakumi	28
23	Xetual	28
24	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:

Sol of the week	Martian Weeksol (1-Letter)	Earth Weekday
1	Heliosol (H)	Sunday (S)
2	Neriosol (N)	Monday (M)
3	Libersol (L)	Tuesday (T)
4	Terrasol (T)	Wednesday (W)
5	Venusol (V)	Thursday (R)
6	Mercusol (M)	Friday (F)
7	Jovisol (J)	Saturday (S)

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 07-Adir-03:523.234.

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

MarsClock is the class that encapsulates the job of tracking time on Mars.

msols is simply the truncated or integer form of millisols. So, if the current millisol is 345.3, then the msol is 345.

How would you convert 1 Earth second to that of millisols on Mars and vice versa ?

We define one millisol of Mars to be 88.775244 seconds of Earth.

Currently, mars-sim does not use decasol (which is ~2.46 Earth hours) or centisol (which is ~14.8 Earth minutes) as units of time.

Since one sol on Mars has 1000 millisols, it has 88775.244 Earth seconds.

In contrast, a day on Earth has 86400 seconds (= 24 hrs * 60 min * 60 secs).

How should we define Time Zones on Mars ?

In future, mars-sim may incorporate a time zone system similar to the Ares Time Zone System as proposed by Ares Astronautics.

This system may create 24 divisions of time zones, each having a wide of 15 degree longitudes, over the entire surface of Mars.

See this for a wealth of information regarding Martian Time.

See also some interesting StackExchange discussions.

Feel free to chime in the discussion in this thread with regard to how we may implement a time zone system in mars-sim.

Over the years, scientists from both NASA and ESA expressed interest in creating a lunar time standard such as Coordinated Lunar Time (LTC) that implies designating lunar time zones.

In fact, because of the the gravitational field strength differences experienced on between the Moon and Earth, time moves quicker on the Moon relative to Earth, at around 56 microseconds every day.

With the on-going effort of returning human beings to the Moon's surface since Apollo 17 in 1972, accurate lunar timekeeping will be more important than ever to enable future colonization and commercial industrial development on our Moon.

Thus, NASA's LunaNet has been developed as the Interoperability Specification for communication and navigation on the Moon.

See this recent news and discussions.

According to this article, a theoretical framework with mathematical models necessary for creating a lunar coordinate time system has been developed by researchers at the National Institute of Standards and Technology (NIST) for precise timekeeping on the moon.