Our concept of time has been fundamentally shaped by the natural rhythms of Earth's interactions with the Sun and the Moon: the day, the month and the year. These are the natural units of time. All others - the second, minute, hour, week, quarter, decade, century, and millennium - are derived from these three. As the cultures of the world have become more integrated, a common system of timekeeping has been universally adopted for civil purposes. The 24-hour clock, with its further divisions into 60 minutes per hour and 60 seconds per minute, is used exclusively throughout the world. The Gregorian calendar has become the international standard for civil time, although a number of other calendars - such as the Julian, Chinese, Jewish, Islamic, and Hindu calendars - continue to be used for cultural and religious purposes.

So why Martian time? Since we have a standard for civil time on Earth, why not export it to Mars in order to maintain commonality? This straightforward idea overlooks the fact that the time standard we have adopted on Earth works for everyone only because we all live on Earth and are subject to all of the same natural cycles. The problem is that Mars has its own distinct natural cycles, and the impact of these cycles on human activities on Mars will be impossible to ignore. Our daily routine will be synchronized with the Martian day, not the Earth day, and it will be the annual passing of the Martian seasons, not those of Earth, that will have a significant effect on our activities.

How long is a day on Mars? Just about any astronomy book will tell you that the rotational period of Mars is 24.6229 hours, or 24 hours, 37 minutes. However, note that the same table also gives Earth's rotational period as 23 hours 56 minutes. But isn't Earth's day 24 hours long? What happened to the missing four minutes? The difference is that the 23 hours 56 minute figure is a sidereal day, i.e., Earth's rotation as measured from the point of view of a fixed reference angle. But as Earth turns once on its axis, it also moves along its orbit around the sun, and the direction from the Earth to the sun changes slightly. It takes Earth an extra four minutes to rotate through this additional angle, and so Earth's solar day, measured from the point of view of the sun, is 24 hours. The same principle applies to Mars. Although its sidereal day is 24 hours, 37 minutes, its solar day is 24 hours, 39 minutes, 35.244 seconds (88775.244 seconds).

Humans have already experienced the need to work according to a Martian daily schedule at times during the past quarter century. During the Viking missions in the 1970s, operations teams had to schedule tasks for the two landers based on the daylight hours at the two sites. A new term - sol - was coined for the Martian solar day. The sol on which each lander touched down was designated "Sol 0," and each successive sol was numbered consecutively. In order to express the local time at each site, the sol was divided into 24 Martian hours, which were in turn divided into 60 minutes per hour and 60 seconds per minute, just as on Earth. This same system was later used during the Mars Pathfinder mission in 1997. Exactly who developed this system? We wish we knew, for we would certainly like for him or her to be recognized.

Notice that the system of time used during the Viking surface operations, and which was later adopted for the Mars Pathfinder mission, made use of only one natural Martian cycle: the solar day. What about the Martian year? Viking Lander 2 operated for 1,280 sols (nearly two Martian years), and Viking Lander 1 lasted even longer - 2,244 sols, or more than three Martian years.

How long is a year on Mars? Just about any astronomy book will tell you that the orbital period of Mars is a bit less than 687 days. But this measurement is in 24-hour Earth days, not Martian sols, which are almost forty minutes longer. If you lived on Mars, you would count 668.5906 sols from one vernal equinox to the next.

On Earth, the vernal equinox (the beginning of spring) is used to define the beginning of the astronomical year. This occurs when the Sun is directly above the Earth's equator, and the daylight and night periods are exactly 12 hours each (the term equinox is derived from two Latin words and translates literally as "equal night"). In organizing data for Martian phenomena that are influenced by the annual cycle, scientists often use the Martian vernal equinox as the starting point of the Martian year. Data is then graphed on a time scale from 0 to 668.6 sols.

The question then arises, how does one refer to one specific Martian year versus another? How do we organize our description of annual phenomena? For the Viking era, this was easy. One could refer to Sol 207 of Viking Year 1, for instance, and compare conditions at a landing site then with the phenomena observed on Sol 207 of Viking Year 3, exactly two Martian years later. But the situation becomes more complicated when one wishes to compare data across two or more Mars missions. A researcher interested in global weather patterns might want to compare data from several orbiter missions obtained during a number of different Martian years. For instance, suppose one needed to refer to a data point on Sol 475 of the second Martian year of Viking Orbiter 1 operations and compare that to a data point on Sol 475 of first Martian year of Mars Global Surveyor operations. This is a rather cumbersome way of expressing what are essentially two Martian dates. To simplify expressing Martian dates, we need to agree on a standard epoch, that is, a starting date from which we all agree to count Martian years.

So far, we have discussed some of the technical requirements for measuring time on Mars. That is a quite narrow perspective, and what we currently have on Mars is a fairly rudimentary time system that serves the needs of a specific community of space scientists. Even so, one can see that as more spacecraft are sent to Mars and as more data accumulates, the need for a more comprehensive Martian timekeeping system grows.

Let us fast-forward to a time in which there is a human society on Mars, with people from all conceivable walks of life, not just scientists, engineers, and technicians, but accountants, artists, and athletes. What sort of timekeeping system will these Martians need? In asking that question, one needs to understand that developing a timekeeping system to serve the broad spectrum of humanity and all of its activities is really not a technical problem. The astronomy of developing a clock and a calendar is relatively straightforward. Once the space scientists determine the length of the sol and the Martian year, their part of the job is pretty much done. Almost anyone can do the math; it's only on the level of middle school algebra. However, the true scope of the problem goes far beyond that, because developing a comprehensive civil time system is mostly a human problem involving social necessity. One needs to understand how human societies organize themselves in the temporal dimension at various social levels. Also, since each human society has done it differently, each of us has a cultural bias when it comes to measuring time. Finally, since there is no obvious best way to organize time for a society, arriving at a universally accepted system of Martian timekeeping will involve developing a consensus via a social process.

Such a process has been underway for several years now, primarily due to the increased access to information and the increased ability to form issue-oriented communities on the Internet. Years ago, from time to time a person would consider the problem of Martian timekeeping and publish a paper in some (often obscure) journal, usually ignorant of the fact that others had published on the subject years before in some other obscure journal or in a book that had a limited printing run. Historically, the subject has not attracted wide attention. It may come as a surprise to you that the roots of Martian timekeeping go far back indeed. A couple of excellent Martian calendars were devised by astronomers in the 1930s and 1950s, and one of these gentlemen went so far as to have a working Martian clock built. Going back even further, the subject of Martian time was discussed in a science fiction novel published in 1880.

In the late 1990s, as the United States recommitted itself to a sustained program of Mars exploration, and the Mars Society was founded with the goal of furthering that exploration to eventually include human missions, bases, and settlements, more people became interested in Martian timekeeping. Nowadays, we find several new Martian timekeeping websites every year. While in the old days, most writers thought they were the first to look at the problem, that is becoming less and less the case. Today, most people who get interested in the subject go online and find at least some of the work that has already been published before they finalize their own ideas. So now, rather than working in isolation, there is an online discussion in progress. We are increasingly being influenced by each other's ideas, and it is in this environment that we can begin to form a consensus.

Consensus will probably develop in phases on an issue-by-issue basis. Some issues may need to be settled in the near future (perhaps the need for a standard epoch is one of these), while others can be deferred indefinitely (the names of the days of the week or the months of the year, for instance). Some issues may not need to be settled early, yet it is possible that there may develop such an overwhelming preference for specific solutions that consensus is achieved rapidly (the seven-day week, for example).

Another factor that will determine how we arrive at a consensus is the rise of various user communities, their specific needs for Martian time, and their influence on each other. The space science community was the first user community to emerge, but its requirements for Martian time are fairly basic. This community will probably be incremental in its approach to Martian time, adopting new standards only as the technical need arises. At the other end of the scale are enthusiast groups who look forward to a future human society thriving on Mars. For some of these groups, a fully-developed timekeeping system, complete with a calendar as well as a clock, is part of the characterization of an emerging Martian cultural identity. These comprehensive time systems may either be developed by the groups themselves or adopted from previously published sources. In any case, these systems will compete with each other by attracting either greater or fewer adherents over time. Some of these enthusiast groups have developed websites and even web-based Mars simulations that feature Martian timekeeping systems. One can speculate that the relative success of the competing systems in the environment of the World Wide Web will be a function of the popularity of their associated websites and not necessarily of the merits of the timekeeping systems themselves.

It may be useful to develop statistical tools to measure - and perhaps even to guide - the development of a consensus. To that end, we created the Martian Time Survey. The survey is currently in its second version. The results of the first version were reported at the Third International Convention of the Mars Society (Gangale & Dudley-Rowley, 2000). The survey records respondents' selection of options for specific aspects of Martian timekeeping, such as the number of primary divisions (hours) in a Martian solar day, or the choice of an epoch for counting Martian years. Thus the individual ideas that have been proposed over the years are deconstructed from their original comprehensive timekeeping packages and the associated cachet of individual authors or specific groups. Respondents can make selections on an issue-by-issue basis according to the merits of the proposed options, rather than choose between whole systems authored by a given person or touted by a specific group. Additionally, in the current version of the survey, respondents are encouraged to propose new options, and to furnish background information on each issue as well as pro and con arguments for each option as they desire. Thus not only can people respond to the survey, they can also influence the evolution of the survey.

Let's now turn to some specific issues.

Going back to the Viking project, the 24-60-60 system was not the only possible choice for a Martian clock. A number of writers on the subject of Martian time have considered clocks based on powers of ten. Technically speaking, there's no reason not to use such a system, and in fact the idea has a great deal of merit. The real issue is, once again, human. The 24-60-60 clock is deeply ingrained in human culture. On Earth, we agree to disagree on a number of other points when it comes to time. We variously prefer Friday or Saturday or Sunday as our sabbatical day, and we maintain a number of cultural calendars. But everyone tells the time of day by hours, minutes and seconds! So it was not unreasonable for the Viking program to stretch Earth's 24-60-60 clock to fit the longer Martian sol. In any case, the precedent for Mars has been set, and metric clock advocates have their work cut out for them.

More information on the topic The Martian Day: Structure

Given the number of cultural calendars that persist on Earth, despite the Gregorian calendar being the agreed civil standard, you can imagine the number of issues that we as a species bring to the problem of developing a Martian calendar.

Some people want to keep the seven-day week, some favor other numbers, and some want to abolish the week entirely.

More information on the topic The Martian Week: Structure

It is very much the same with the month. Some want to retain the 12-month year, while some think this makes for awfully long months (remember that the Martian year is nearly twice as long as Earth's) and would rather have twice as many in order to keep them to about the same number of days as Earthly months. Some want to keep the structure of the year simple and have months that are nearly equal in duration. Others, taking note of Mars' lopsided orbit, think that the months should span equal arcs of that orbit, even though this means that each month would contain a different number of sols (presenting a challenge Martian poets to come up with a mnemonic poem that would be truly memorable, if not very short). Then again, some want to abolish the month altogether.

More information on the topic The Martian Month: Structure

The season in which the calendar year should begin is another point of contention. Some favor the vernal equinox, others the winter solstice or another astronomically significant point, and still others still have picked arbitrary points in Mars' orbit to serve as the first sol of the year.

Picking a leap year system is far from simple either. The year lasts about 668.6 sols, whereas the length of each calendar year must be a whole number. There are leap year schemes that contain a pattern of 668-sol and 669-sol years. Other schemes include double leap years of 670 sols. Others ideas involve adding entire leap weeks or leap months.

Once one has decided on how many extra sols to have in leap years, when should those extra sols occur: at the beginning of the year, at the end of the year, or somewhere in between?

One idea for improving on the Gregorian calendar is to have each year begin on the same day of the week (Sunday, for instance). A number of ideas for reforming the Gregorian calendar that were proposed in the 19th and 20th centuries involved making it perpetual, that is, making each common year and each leap year begin on a Sunday and end on a Saturday. The fact is that the Gregorian calendar isn't really a single calendar but rather a set of 14 different calendars. A common year can begin on any of the seven days of the week, and so can a leap year. This is why you have to throw out your old calendar at the end of each year and buy a new one. Extending this idea of regularizing the calendar, each month could begin on the same day of the week. This would have the advantage of always placing the numbered day of the month on the same day of the week (one would know that the 16th always falls on a Tuesday, for example).

Assuming that we want to have a perpetual calendar on Mars, how do we implement it? If we keep the seven-day week, we have to come up with some deft manoeuver to get around the fact that neither 668 nor 669 are divisible by seven. Some solutions add one or more sols that fall outside the normal weekly rotation of seven sols, and these extra sols are counted as holidays. Another idea is to have an occasional six-sol week, eliminating a workday. Alternatively, one could have a number of sols at the end of the year that either comprises an irregular week or are outside the weekly rotation. Still another scheme is to have 665-sol years (divisible by seven) and add a seven-sol leap week as necessary.

More information on the topic The Martian Year: Structure

Finally, as we touched on earlier, there is the question of determining an epoch, a starting point for counting the Martian years. Ideas range from dates thousands of years in the past (such as the beginning of the Julian period), to much more recent events (such as the landing of Mars 3 or Viking 1), to waiting for the first human landing (which of course makes it impossible to count Martian years in the meantime).

More information on the topic The Martian Epoch

These are just the structural issues of characterizing a complete calendar system. We haven't even begun to discuss the problem of nomenclature. Should all of these Martian units of time - the second, minute, hour, week, month, and year - have new Martian names to distinguish them from Terran time measurements? What should we name the sols of the week and the months of the year? Such issues do not lend themselves to logical arguments, but are rather a matter of personal taste. This class of issues will probably be the last to be resolved.

Further information:

As you can see, there's far more to Martian timekeeping that we can possibly cover in one short article. We invite you to visit the Martian Time website to learn more. Also, feel free to join the Martian Time Virtual Conference and share your ideas. Finally, the crucible of all the ideas that have been put forth is how they will be received by Martian society, and at present, you, dear readers, are Martian society, and so we hope you will take the time to register your preferences in the Martian Time Survey.

CopyrightA9 2002 by Thomas Gangale and Marilyn Dudley-Rowley.

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An autumnal complaint about the "vernal" equinox!

Hey there, there IS a southern hemishpere, you know, even on Mars. All through your fascinating discussion, you blithely write of the "vernal" (spring) equinox as if there is no possible ambiguity. This is simply false: what you should be writing about, of course, is the NORTHERN HEMISHPERE vernal equinox. To leave out these vital two words shows a shocking prejudice!!!

For instance, you poor northern types suffer the delusion that Easter is a spring festival, whereas we fortunate and enlightened southerners know of course that Easter REALLY occurs in the "season of mists and mellow fruitfulness"....

HELP STAMP OUT NORTHISM!!! :-)

David Betty
Sydney, Australia

Aaaaaaahahahaha, yeah!

You made my day with that one David. :)

And David writes his comments on the 4th day of the 27th month in the year 02....how peculiar! :oP

We use the European system of dates on New Mars (dd/mm/yy).

I was not familiar with Mars chronology, but I had a kick browsing through the sites concerning it when I found them. Here is my opinion as a novice: the 24 months system seems the easiest and the more commonsensitic. In case of mars colonisation, I guess people will have a hard time with month of different length. It may fit the seasons, but you can't work and plan properly with that. Also 28 days months seems perfect, since it does not only closely fits a millenium-all tradition, but also the body cycle of half of world population.

As for their names, I kind of like the Gangale proposition :
Sagittarius, Dhanus, Capricornus, Makara, Aquarius, Kumbha, Pisces, Mina, Aries, Mesha, Taurus, Rishabha, Gemini, Mithuna, Cancer, Karka, Leo, Simha, Virgo, Kanya, Libra, Tula, Scorpius, Vrishika.

Though it is a bit complicated to write, a bit lengthy. Why not simplify it somewhat? GANGALE SIMPLEX : Sagittar, Danno, Capricorn, Macara, Aquario, Comwa, Pisce, Minna, Arie, Mesha, Tauro, Rishwa, Gemini, Mithna, Cancer, Carca, Leo, Simma, Virgo, Canya, Libra, Tula, Scorpio, Weshca.

Also new names can also be coined, as in the following proposition (in which the first 19 months' names are based on latin stems, while the four last are based on astronauts' names):
JHOLO : ummon, dumon, trimon, quarmon, kimmon, sismon, semmon, oimon, nommon, decmon, ondeon, dodeon, trideon, quardeon, kindeon, sisdeon, seddeon, oideon, noddeon, deddeon, gagareon, amstreon, aldreon, colleon.

But another idea would be to simply number the months (as the Japanese do now for the terrestrial months) : M1, M2, M3, etc. up to M24. Each user will form an habit of reading them in her own language. Eventually a norm will set up in this language. In English, it could lead to sentences like "let's have the next meeting in M-one next rev" (or : "in Month One").

I don`t know very much about the Mars and Earth chronology but I have some ideas about this. I think that is not necessary have 680 days for year. We don`t need a calendar for know the stations, it can be knowed by us with the computers. Ah year of 350 martian days is good, I think. It can be divided with 10 months of 35 days and 50 weeks of 7 days. The months can be named by writers of science-fiction, scientists... The day can be divided by 10 hours, and 1000 seconds.

Jose Diego, Murcia, Spain

Venusday (Friday), 6th of Mivsam, 3200mce (4th of April 2003ce) @ 1:40 UTC. This is a calendar that was at least 25 years in the making. This is the 25 month Marian Calendar. Nevayot,_Kedar,_Adve-El,_Mivsam,_Mishma,_Dumah, Massa,_Hadad,_Tema,_Yetur,_Napish,_Kedemah, Reuven,_Simeon,_Lewi,_Yudah,_Dan,_Naptali, Gad,_Asher,_Yissachar,_Zevulun,_Dinah,_&_Yosep, with 28 (24_hour) days and Ven-Yamin with 15 (24_hour) days. Mars is also on Universal Time Co-ordinated. This is a simple calendar, take it or leave it. Thank you.

Jupiterday (Thursday), 12th of Mivsam, 3200mce [Martian_Common_Era] (10th of April, 2003ce) @ 22:52 UTC. We completely neglected to put in the seasons. They will be presented as Northern_Hemisphere/Southern_Hemisphere. Spring/Autumn begins in the 16th month (Yudah_7th), Summer/Winter begins in the 23rd month (Dinah_9th), Autumn/Spring begins in the 6th month (Dumah_11th), and Winter/Summer begins in the 10th month (Yetur_17th). You may notice that Spring/Autumn is 7 months & 2 days long, Summer/Winter is 7 months & 17 days long, Autumn/Spring is 4 months & 6 days long, and Winter/Summer is 5 months & 18 days long. Thank you.

Jupiterday (Thursday), 12th of Mivsam, 3200mce (10th of April, 2003ce) @ 23:21 UTC. The second. The International scientific community has decided that the second international (or universal) unit of time measurement. The second is " ...defined as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133." which means that there can not be a "Martian Second". What are the options for Martian Time? A. Have a Martian clock that runs from 0:00:00.000 to 24:39:35.243 B. Use Universal Time Co-ordinated C. Divide the Martian Solar Cycle or "sol" into 10 horateens (Hora Spanish for hour, teen for tens of units) then divide the horateen into 100 minteens then divide the minteen into 100 secteens. "B" is the more practical one. Thank you.

Jupiterday (Thursday), 12th of Mivsam, 3200mce (10 of April, 2003ce) @ 23:37 UTC. The Days Of The Week. The names of the days of the week came from the Greco-Roman equivalent of the Norse deities whose names were used to create the days of the week. Solday (Sunday or the Sun'sday), Lunaday (Monday or the Moon'sday), Marsday (Tuesday or Tiw'sday), Mercuryday (Wednesday or Woden'sday), Jupiterday (Thursday or Thor'sday), Venusday (Friday or Frigg'sday), & Saturndayday (Saturday or Saturn'sday). Thank you.

Venusday (Friday), 13th of Mivsam, 3200mce (11th of April, 2003ce) @ 0:03 UTC. David K. Seid of St. Joseph County, IN, The Nation State of America is a WAR CRIMMINAL. 10 years ago on Tuesday, 20th of April (Hitler's birthday), 1993ce he (with two armed "men") kidnapped Frederick Peter Aaron Rupe (>3yo) from his Great Grandmother's home. He is still AT LARGE. The ILLEGAL and CRIMINAL organisation he works for is still in business. This organisation has been at war with Earth's poor for over 4 centuries. An Unreported and undeclared war. If we don't stop these criminals here on Earth they will spread to Mars! In IN they are called the "F.S.S.A." or "social services". We call them the S.S. and the C.P.S. is the Child Procurement Services. They are a business that makes billions off of Earth's poor. They need to be stopped at least for the sake of Mars! Thank you.

Jupiterday (Thursday), 19th of Mivsam, 3200mce (17th of April, 2003ce) @ 23:37utc. There was something mentioned about Mars's two moons Damon ("Deimos") and Phintias ("Phobos"). Something about changing their names. We would like to keep the original names of Damon (for "Deimos")and Phintias (for "Phobos"). Thank you.

Venusday (Friday), 20th of Mivsam, 3200mce (18th of April, 2003ce) @ 0:15 utc. The 25 month Martian Calendar started on Saturnday, 1st of Nevayot, 0 mce @ 0:00:00 utc. It is similar to the Terran Calendar which does not start on the first day of Spring/Autumn nor on the first day of Autumn/Spring. On Earth Spring/Autumn begins on March 21st, Summer/Winter begins on June 21st, Autumn/Spring begins on Sptember 21st, and Winter/Summer begins on December 21st. Thank you. P.S.-The actual dates may vary by a couple of days.

I have a school project, don't get me wrong I will do work, but I have been to a lot of web sites and they are really confusing. Can any one explain it to me simply?

Jupiterday (Thursday), 26th of Mivsam, 3200mce (24th of April, 2003ce) @ 23:36utc. The idea is to invent a clock and a calendar for Mars. The problems are 1. whether to use the 24_hour Universal day or the Martian Solar Cycle of 24_hours, 39_minutes,& 35.244_seconds 2. How to (if needed) divide the Martian day and the Martian Year. We promote a system that is more user friendly and does not require exotique technology or programming. Thank you.

Jupiterday (Thursday), 26th of Mivsam, 3200mce (24th of April, 2003ce) @ 23:58utc. First- It came to our attention that there was some confusion regarding C.E.(Common Era) on Earth. 99_BCE to 0_BCE was the First Century BCE (0_BCE=2_BC). 0_CE to 99_CE was the First Century CE (0_CE=1_BC). 1900_CE to 1999_CE was the Twentieth Century CE. 2000_CE was the begining of the Twenty First Century CE. Second- The Martian Common Era started on the Holy Millennial Shabat. There is an old Martian saying that "when the Divine Spirit ended it's creating time began". Thank you.

Dear Earth people
I know I was strictly forbiden to interfere with your local affaires by my own people but I can't resist to gave you some bit of information in the subject of time in my own planet.

- The year duration is 668.5906 local solar days;
- There are 4 major orbital point marks: Inner solstice, Outer equinox, Outer solstice and Inner equinox
- Year starts in the orbit's nearest point to the Sun, the Inner solstice;
- There are 4 seasons begining in each of the 4 major orbital point marks;
- Each season has 4 months with 42 days except for the 4th month that has only 41 days;
- Each month is roughly divided into 6 sub periods of 7 days (a week ?) but in shorter months the last period has only 6 days;
- Leap years are alternate but each 5th year also became leap except for the last year of a century;
- In leap years the last month of the year (4th month of 4th season) has also 42 days;

With this schema each century will still be 0.06 day shorter than the real century.
- So in each 16 centuries the last year of the century will also became leap;
- A small residual excess will require a day to be removed each 368 centuries by not making the year leap.

Remaining differences are not significant to be taken in consideration in the nearest 3 million of our years (about 6 million of yours)
because they are less then a day long so there is no need to explain you the remaining corrective rules.

Let me show a few examples to make things clear for you:

Months duration within a season
Month days
- 1st.. 42
- 2nd.. 42
- 3rd.. 42
- 4th.. 41

4th season months duration in a leap year
Month days
- 1st.. 42
- 2nd.. 42
- 3rd.. 42
- 4th.. 42 (last month of the leap year)

Leap years sequence
Year Days
- 0.. 688
- 1.. 689
- 2.. 688
- 3.. 689
- 4.. 689 (5th year)
- 5.. 698
- 6.. 689
- 7.. 688
- 8.. 689
- 9.. 689 (5th year)
...
- 95.. 698
- 96.. 689
- 97.. 688
- 98.. 689
- 99.. 688 (last year of the century)

Has for the day division we really do not worry a lot about it. Just morning, afternoon and night. We don't run on clocks.

I hope you all can enjoy our local experience with this calendrical things regarding our own planet. In return I was hoping one day one of you will explain me your own multiple calendars so I can finally understand how they work together!
Thank you.

Oops!

I must, somehow, have bin affected by your toxic atmosphere to make this kind of mistakes...

Let me correct the examples above.

Leap years sequence
Year Days
- 0.. 668
- 1.. 669
- 2.. 668
- 3.. 669
- 4.. 669 (5th year)
- 5.. 668
- 6.. 669
- 7.. 668
- 8.. 669
- 9.. 669 (5th year)
...
- 95.. 668
- 96.. 669
- 97.. 668
- 98.. 669
- 99.. 668 (last year of the century)

There it is. Now it is correct. The excess of oxygen in your atmosphere sometimes do this kind of tricks to our foreign minds.

Have a nice Outer season.

Jupiterday (Thursday), 12th of Dumah, 3200_MCE (5th of June, 2003_CE) @ 22:15_UTC. Aefvadh! At last we know the true calendar for Mars! ;] But us poor feeble Humons on Earth need a system that will easily interface with our current calendar systems. This is why we feel our system is the best (for now at least). Maybe later we will be able to adapt to your system, Thanks anyway. Thank you and K'Plah!

Dear Earth people

The problem of an easy interface between Earth based and Mars based calendars have already crossed our minds a few times (specially for the few of us designated to locally observe Earth).
Our calendar is natural to us as it is based on a few logical concepts:
- A 4 based year division, after the 4 major orbital points, with seasons that are also divided in 4 months each;
- The year was designated to start in a logical point, in this case the orbit's nearest point to the Sun (that is the reason why it was named Inner - not only the solstice itself but also the equinox; those 2 seasons are what we call the Inner part of the year);
- Calendar should be perpetual: month dates occur in the same week day every year (that is why in shorter months the week has also less a day, in Earth this missing day could also be a work day ;)
- Calendar corrections should occur were they cause less perturbations, that is why;
-> Seasonal correction take place only in the last day of a season so the next major orbital point is as near as possible where the calendar say it is;
-> Leap year corrections take place only in the last day of the year, for the same reason, and in an alternate cycle so the first year acumulate a delay of 1/2 day while the second year starts with 1/2 a day of advance. They are corrected in the end of the 2 year period.
-> Other Leap year corrections also has the same principles and take place where required to force the calendar to be syncronized with the major orbital points.

Of couse in the last few millenia we have seen the basic Earth tendencies evolve since the Sumerian calendar and understand the 12 and 60 based cycles that were originated there (but that does not make them easy for us to understand).
What we do locally is simply follow your calendar without report it to our own calendar. That is not possible in a logical way because the orbit of both planets do not agree with that. It should be easier if your planet had an orbit, for instance, exactly half the duration of ours. The way things are we report each time in their own calendar units.

The question of the day division is easier for us to handle: we dont have a standard day division, so when we need we adapt yours.
For that we 'enlarge' the minute only and keep all the other divisions. The diference is barely noticeable:
- Seconds are seconds, has defined by the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133;
- A Martian day has 24 hours and a Martian hour has 60 minutes;
- However a Martian minute has 61.5417 seconds;
For the normal day to day stuff those extra 1.5417 seconds in the minute duration are not noticeable and the hour is only 92.502 seconds longer than in Earth. Of course this is only possible because, as we dont run on clocks, 37 minutes more or less in the day duration make no difference at all. The only problem is to convence clocks to handle those extra 1.5417 seconds each minute. Special Mars clocks and watchs are required, everything else works fine. Perhaps one day Earth will have a brand of clocks named 'MWATCH' ;)

However if we need to define an accurate time interval for something that must have a common base between Mars and Earth time we use seconds with scientific notacion, for instance:
- Mars day is 88.62x10^3 seconds long (wich is 24:00 MT - or Mars Time);
- Earth day is 86.4x10^3 seconds long (wich is 24:00 ET - or Earth Time).
- Earth sideral day is 86.16x10^3 seconds (wich is 23:56 ET).

Have a nice Outer season.

I am a bit of confused - "Year starts in the orbit's nearest point to the Sun, the Inner solstice;" -- even here on Earth the soltices are not coincidental with apsides, the (Northern) winter solstice taking place a dozen days before the perihelion (at present days), or 12 arc degrees difference.

Mars perihelion is about 29 sols before the solstice, i.e. 15 degrees. So? when does the year start?

Dear Earth people

My apologies for taking so long to return to this lovely site. I've bin away, I guest you know where. I had to use this marvelous approach opportunity for a quick trip back home. Anyway I got authorization to continue writing here (not there) as long as I stay anonymous...

About the relation between orbital points and the seasons: the Inner solstice occurs in the orbit's nearest point to the Sun. The Outer solstice occurs in the orbital far point. Neither coincide exactly with the perihelion and aphelion. Those are different definitions. However the Inner solstice occurs, from an orbital point of view, very near the perihelion. But, for traditional and practical reasons, the year starts in the solstice, not at the perihelion.

The 4 based year division was done 'after the 4 major orbital' points not 'at the 4 major orbital points'. I suppose that from a pure logical point of view this looks like a wrong choice but I guest traditions and practical issues have a lot to say in this subjects.

Have a nice Outer season.

Venusday (Friday), 13th of Yetur, 3200_MCE (26th of September, 2003_CE) @_1:19_UTC. Aefvadh! Having looked at "silent martian observer"'s 16 month calendar one wonders if "smo" had intended it to start in winter? Not to mention the fact that the seasons differ greatly (e.g. Spring/Autumn w/ 7months&2days, Summer/Winter w/ 7months&17days, Autumn/Spring w/ 4months&6days, and Winter/Summer w/ 5months&18days. You can;t put Mars in a box. Marsday (Tuesday), 17 of Yetur, 3200_MCE (30 of September, 2003_CE) will be the first day of Winter/Summer [as far as we can figure from our calculations] and it will be an "inner season". Earth's Summer/Winter is an "outer season". This is why Mars and Earth are so close. Thank you and K;Plah!

Dear Earth people

When we call a season 'inner' we refer only to the orbital path that the season is covering. No inferences should be done about 'weather' seasons has they do not really apply here. It only happens that for the moment our perihelion and the inner solstice are quite near. You see this things are not has easy has they could be (and the same applies to Earth). Both of our planets has 'weather' seasons because their axis are tilted (very similarly) relatively to their orbital planes. This inclination defines the starting and ending point of the 'weather' seasons because it is responsible for the orbital location of the equinoxes and solstices. However this things aren't fixed. The polar axis inclinations changes slowly in time and so does equinox and solstice dates (the same happens to Earth).This cycle last about 41,000 orbits (or about 75,000 Earth years) and it is called precession.

Because the direction of the planet's axis determines when the seasons will occur, precession will cause a particular 'weather' season (for example, northern hemisphere winter) to occur at a slightly different place in the orbit from year to year. At the same time, the orbit itself is subject to small changes, called perturbations. The orbit is an ellipse, and there is a slow change in its orientation, which gradually shifts the point of perihelion in space. The two effects - the precession of the axis and the change in the orbit's orientation - work together to shift the seasons with respect to perihelion. Thus, for a calendar aligned with the occurrence of the 'weather' seasons, the date of perihelion gradually regresses through the year. It takes about 27,000 orbits (or 51,000 earth years) to make a complete cycle.

There is a third, and very important, cycle. The eccentricity of the orbit (how elliptical it is) also changes over very very long periods of time, from almost zero (circular orbit) to about its current value. And this have a huge influence in our climate, atmosphere composition and density and consequently in the definition of 'weather' season itself.

For all of those reasons we do not use a 'weather' season but rather equally divide 'orbital' seasons, not really related with the real duration of the 'weather' seasons.

The system is not perfect. The main reason is that the present calendar definition is still suffering from 'compromises with ancient traditions' and tries to make some vague correspondence between 'weather' seasons and 'orbital' seasons when it defines that the year starts in the solstice orbital point nearest to the Sun. This make the perihelion shift within the 2 inner seasons until the point where the definition of 'Inner' season has to shift itself: the Outer season became the Inner season.

For this reason (is my personal believe that) the next calendar revision will fix part of this issues by defining a year starting at the Perihelion, period.

This will produce a cleaner calendar. If we cannot rely on 'weather' seasons on the long run there is no point in force the calendar to go after them: is much more logical to chase the perihelion instead. And practical reasons are no longer an issue because nowadays is as easy to determine the perihelion's date as in the past was to find the inner solstice.

Of course this will introduce other issues (namely a new schema is required to compensate long term perihelion drift) but we are still far way from those 'problems'.

Have a nice Inner season.

--See first posted comment--
A continual complaint about the equinoxes (or should it be equinoxii?)!

Hey there, there IS NOT a southern hemishpere, you know, on Mars our planetary metal core has solidified, ending our planetary magnetism. All through your fascinating discussion, you blithely write of the "vernal" (spring) equinox as if there is no possible ambiguity. This is simply false: what you should be writing about, of course, is the "GREAT BEAR" OR "BIG DIPPER" HEMISHPERE equinox. The other equinox being the "SOUTHERN CROSS" HEMISHPERE equinox. To leave out these vital two definitions shows a shocking prejudice!!!
Silent Martian Observer has made a lot of good calendar points, but I'm sure that having the start of the year beginning on the day of the closest approach to the sun (like the earth) makes sense. For the earth, this point moves much slower than the equinoxes due to precession.
To save confusion the the "day" for any planet could be thus:- esol =Earth day, masol =Mars day, mesol =Mercury day etc.
The reference year is from an obvious astronomical event. The -Mars year- that Mars had its closest approach to Earth becomes -Mars year- 1000 of course. About 1825 Earth years ago was -Mars year- =0

For instance, you poor northern types suffer the delusion that the compass needle always points to the (North) Pole star. Well here on non-magnetic mars your Pole star isn't ours to point to and the compass doesn't work anyway!

HELP STAMP OUT MAGNETISM!!! :-)