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Timekeeping
Revised : 03 Apr 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]** |
Note
For *, see section E below. For **, see section F below.
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).
Note
A sidereal day on Earth has 86164.0905 seconds (or 23 hrs 56 mins). One sol on Mars spans longer than one day on Earth. One sol is 39 minutes and 35 seconds. As previously stated, one non-leap Martian year (or orbit) has 668 sols (or 687 Earth days).
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.
Over the years, scientists from both NASA and ESA expressed interest in creating a lunar time standard such as Coordinated Lunar Time (CLT) 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 58.7 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 for future commercial development.
Thus, NASA's LunaNet has been developed as the Interoperability Specification for communication and navigation on the Moon.
See recent news and 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.