Calendars and Clocks for Mars

A day on Mars consists of 24 hours, 39 minutes, and just over 35 Earth seconds. And there are about 669 of those days, also known as sols, in a Martian year. So, on the Red Planet, Earth clocks and calendars are useless. But what are the alternatives?

People on Mars

A calendar for Mars? Don’t you have anything better to do, Mr. Blok? Okay, I won’t solve current world problems like war, climate change, or barrel organ terror with it. But I’m an optimist; I believe that at some point, people will live on Mars. Perhaps many people, and perhaps on a somewhat modified Mars. It’s becoming less likely each year that I’ll experience it myself, but it remains a fascinating thought.

Immortality

Those future Martians won’t be able to use a regular watch or a calendar with 365 days. So, this presents an interesting design challenge. A design task that, for now, offers no monetary reward, only honor. A lot of honor, though; in fact, eternal fame or, you might say, practical immortality. At least in theory.

Because a work from my webshop might hang on someone’s wall for ten years. If I design a building, with a bit of luck, it’ll stand for a hundred years. But a calendar for Mars might last for thousands of years. The Islamic calendar has been used for over 1400 years, the Hebrew calendar in its current form for nearly 1700 years, and the Hindu calendar goes back some 3000 years. The Gregorian calendar, used in much of the world today, is actually quite young: only 450 years old. But as long as civilization doesn’t completely collapse, I don’t expect it to be replaced anytime soon.

Study group

The concept of timekeeping on Mars has been pondered for a long time. Around 1900, American astronomer Percival Lowell already proposed a calendar. But authors like Edgar Rice Burroughs, Robert Heinlein, Arthur C. Clarke, and Kim Stanley Robinson have also contributed their ideas.

NASA uses a sort of primitive calendar for landers and rovers on the Red Planet: sol1, sol2, sol3. Here, “sol” is the official term for a Martian day. Who coined the name “sol” is unknown, but the term is now fully entrenched.

Around the turn of the century, I participated in an online study group on the subject, set up by the Mars Society: the Mars Time Group. The committee did not reach a unanimous recommendation, but then again, the issue isn’t that urgent. The first permanent residents of the planet can make a decision on it when the time comes. But it’s nice if they have a few well-considered proposals to choose from.

Clock

As for the clock, there are really two possibilities: either you stick to the length of the second, or you stick to the division into 24 hours.

In the first case, there will be 39 minutes and 35 seconds after midnight before a new day begins. Kim Stanley Robinson called this the Martian Timeslip. In his Red Mars, the colonists enjoy having those extra almost three-quarters of an hour at the end of each day. But Robinson doesn’t answer a few practical questions: how do you divide such a day into three shifts? And how do you divide the planet into time zones?

If you divide the day on Mars into 24 hours of sixty minutes, each with sixty seconds, those time units will be longer than their Earthly counterparts. Not much longer, but still. And that’s confusing. How, for example, do you compare world records in the hundred-meter running if a Martian second is longer than an Earth second?

Of course, you could also divide a day into completely different units. Into 10 zogs of 1000 kargats or 21 blabs of 67 pipras, for example. But is that really a good idea? As for me: if I had to choose, I’d go for the first option, the timeslip.

Sun and moons

When it comes to the calendar, the choices are much more complicated. Should you, for example, base it on a solar year? On Earth, there are many calendars where the Moon is more important. However, Mars has two moons, Phobos and Deimos. They orbit in just over 7 and 30 hours, respectively; not exactly a cycle to base something like a month on.

Moreover, both moons are much smaller than our own Moon. Phobos has a diameter of 22 kilometres; Deimos is only half that size. As a result, the Martian moons are much less prominent in the sky. So, it makes more sense to base a calendar on the 668.5907 Martian days it takes the planet to orbit the Sun.

24 months

That number, let’s round it to 669, can obviously be divided in many ways. But you won’t get a neat round number. A system of leap days will always be necessary to ensure the calendar doesn’t fall out of sync with the solar year.

There are several reasons why 24 is the perfect number of months. To begin with, it results in months of 28 days. And that’s easy to get used to; after all, we have good experiences with February. Moreover, those 28 days can be divided into exactly 4 weeks of 7 days. And that seven-day week also feels familiar. Additionally, if each month has exactly four weeks, every date always falls on the same day of the week. And that’s handy for scheduling appointments.

Finally, those 24 months can be divided in many ways. Into two half-years of twelve months, somewhat comparable to an Earth year. Into four quarters of six months or six quadrimesters of four months. In eight trimesters of three months, three octomesters of eight months, or even into twelve pairs of two months. And that’s handy for planning events that don’t take place every month.

Leap years

The mathematicians among us have probably already figured it out: 24 x 28 = 672. Indeed, as mentioned, it doesn’t quite add up. But that can be fixed by dropping one day in the last week of each quarter. Preferably, of course, a weekday; even on Mars, a short workweek is something to look forward to.

We’re not quite there yet; to make the calendar fully accurate, the aforementioned leap day is necessary. It falls on the last day of the last month, which has 28 days in leap years.

If we make all odd years leap years, as well as years divisible by ten, with an exception once every 500 years, we’re set. According to this calendar, there are more leap years than non-leap years. A good thing for people born on such a leap day…

Darian calendar

A prominent member of our study group was Thomas Gangale. In 1985, he had already come up with a calendar based on the above principles, which he called The Darian Calendar (named after his son Darius). As for me: perfect, don’t change a thing; this calendar can be used by the future Martians for the next few thousand years (or longer). However, I’d like to think a bit longer about the months and weeks.

Latin and Sanskrit

Thomas suggested naming the months after constellations, alternating between Latin and Sanskrit: Sagittarius, Dhanus, Capricornus, Makara, and so on. But those are all Earthly names; on a new world, you’d rather come up with something new. The constellations are also a bit cliché; especially those Latin names, I’ve heard them just a bit too often. Moreover, learning 24 names by heart is quite difficult for newcomers. Incidentally, everyone on Mars will be a newcomer for a long time.

Mnemonics

So I came up with my own system, based on a few simple mnemonics, which resulted in 24 melodious and pronounceable names. Since I don’t have children, I named that system after my hometown. The Rotterdam month naming system, as a variant of the Darian calendar. You could also call it the Rotterdam calendar, but that’s for those future Martians to decide.

The first letter of the month name is determined by alphabetical order, with Q and Y omitted for convenience. Odd-numbered months end with a consonant: R, N, or L. Even-numbered months end with a vowel: A, I, or O. Every fourth month has a D in its name. In the autumn and winter, at least in the northern hemisphere, the names contain a U, similar to the R in our months. On Mars, children will learn that they should eat lots of fruits and vegetables when there is a U in the monthname.

Seasons

Children also learn, through play, something about the connection between Mars’ orbit and the seasons. Unlike Earth, Mars has a somewhat elliptical orbit around the Sun, so the planet doesn’t always move at the same velocity. The speed is slowest during aphelion, the farthest point from the Sun. This occurs in the spring, making that season longer and autumn shorter than average. Spring has seven months, autumn has five, and summer and winter each have six months. At least in the northern hemisphere; in the south, it’s the other way around.

These differences are reflected in the month names. In the (northern) spring, the months have two syllables; in summer and winter, three syllables; and in autumn, even four syllables. To indicate that months 6, 12, 18, and 24 are (usually) one day shorter, these four have one less syllable and one less letter than their “seasonal counterparts.”

For variety, I’ve also distributed some diphthongs like EO, IU, and OA across the months, as well as consonant combinations like NG, SJ, and RN. This resulted in 28 names that I think sound pleasant and are easy to pronounce in many accents. And as far as I know, they don’t mean anything inappropriate in any language, although you can never be completely sure. The full list: Adir, Bora, Coan, Deti, Edal, Flo, Geor, Heliba, Idanon, Jowani, Kireal, Larno, Medior, Neturima, Ozulikan, Pasurabi, Rudiakel, Safundo, Tiunor, Ulasja, Vadeun, Wakumi, Xetual, Zungo.

Days of the Week

Later, I devised a similar but slightly simpler system for the days of the week. Here too, the goal was to create fresh, new, pleasant-sounding names. Gangale uses the Sun, Moon, and five planets for this; I suggest an alphabetical order instead. The weekdays have two syllables, and on the weekend, there are three. After all, on the weekend, you have more time to pronounce those syllables. This yields the following names: Gaviosol, Benasol, Ciposol, Domesol, Erjasol, Fumisol, Gaviosol. The observant reader will notice immediately: according to the Darian calendar, the weekends fall at the beginning and the end of the week.

Telescopic epoch

There’s one last question that remains unanswered: when should we start counting the years? In technical terms: what is the epoch of the calendar? The “Neil Armstrong moment,” the first manned landing, would be a good starting point. But that’s still in the future, and no one knows how far off. So, we wouldn’t know what year we’re currently in.

Gangale initially chose the landing of Viking 1 in 1976 as the starting point for his Darian calendar. But upon reflection, he found that too America-centric. More importantly, it would mean that many events in Martian history happened before the common era, in years with a negative number, which was considered needlessly clumsy. Peter Kokh, another member of our study group, suggested to use the the Mars year coinciding with 1609/1610. That was the beginning of the telescopic era in the study of the Red Planet.

During those years, Galileo Galilei was the first to observe Mars through a telescope. Around the same time, Johannes Kepler published his first two laws of planetary motion. In short, it was a good Mars year, beginning at the spring equinox in the planet’s northern hemisphere, dated March 11, 1609. This means we are now in the year 220. I certainly hope that the first manned landing happens sometime before the end of the twenties. Or, as John F. Kennedy might put it: “We choose to go to Mars, before this decade is out.”

Converter

I still plan to develop an app that makes it possible to calculate the current date on Mars from this page. A simple converter from the Gregorian to the Rotterdam/Darian calendar and vice versa. But that requires some advanced programming work, which I’m not trained for.

For now, I refer to the converter on Thomas’s site. The downside is that it only includes the Latin and Sanskrit month names; the big advantage is that it also provides historical events that happened on the corresponding day.