Mare Chronium

A Brief History of Martian Time
1880-1999

An expanded and updated version of a paper presented at
the Case for Mars IV Conference, University of Colorado, Boulder, Colorado, USA
4 - 8 June 1990

Copyright © 1990, 1997-1999 by Thomas Gangale

Part 4

On the Victorian Space web site, Damon Dean has devised a timekeeping system for an indigenous Martian culture whose mathematics are based on the number eight. The Martian day is divided into hours, sub-hours, minutes, sub-minutes, seconds, and sub-seconds. The day begins with sunrise.

A serious flaw in the system is that it is based on a Martian day of 24 hours, 37 minutes. This the approximate length of a Martian sidereal day, but is two and a half minutes short of the Martian solar day.

Even if the correct value for the Martian solar day were used, basing the beginning of the day on the moment of sunrise would present some challenges. For any given longitude, the moment of sunrise varies with latitude. In summer, the further you are from the equator, the earlier the time of sunrise. This seasonal effect also means that the time from one sunrise to the next varies throughout the year, and is always either longer or shorter that the mean solar day.

Alan Dechert's calendar is not a fully developed system. For instance, he states, "There are about 670 Martian days in the Martian calendar." From this, he suggests a calendar of eleven 56-sol months and one 54-sol month, "with leap years here and there." The names of the seven days of the week and the twelve months remain as they are on Earth. His rationale for preferring a 12-month calendar over a 24-month calendar is that:

... as with the days of the week, you could use the same names as we use on Earth. Furthermore, the calendar could be started in such a way that the Martian seasons would correspond to the same months as they do on Earth. That is to say, January on the Martian calendar would correspond to mid winter in the northern hemisphere, spring would begin in March, etc., etc.

Of course, to have the Martian seasons correspond to the same months as they do on Earth, and at the same time have months of equal duration, is impossible because the eccentric orbit of Mars causes the seasons to be very unequal in duration. Only a stretched Gregorian calendar, in which the months vary in length from 47 to 66 sols, can fit this bill.

Dechert does not specify which month contains only 54 sols, or when the leap sol occurs, but since his calendar is clearly intended to perpetuate many of the features of the Gregorian calendar, it seems likely that February would be the answer to both of these questions.

Dechert first considers setting the epoch to 1 A.D., then favors modern alternatives:

It may make more sense to begin the Martian calendar with the year zero to mark the beginning of human civilization on Mars.

It could also be part of the Year Zero celebration on Earth to kick off the Year Zero on Mars at the same time. In this case, it would not mark the actual beginning of human civilization on Mars but would symbolize the beginning of our plan to colonize Mars.

For 1 January on Mars to occur on the same L_S as it does on Earth, and to have the Martian Year Zero begin near the beginning of the new millennium on Earth, places the epoch on 6 January 2000.

Dechert's Martian clock is the familiar stretched Earth clock, based on a Martian second that is nearly three percent longer than the standard Earth second.

Josef Šurán's article "A Calendar for Mars", published in Planetary and Space Science, dealt with intercalation methods for handling the fractional remainder of the 668.592-sol Martian year. He began by distinguishing between two basic calendar types: leap calendars and skip calendars. The distinction seems to be merely a semantic one, however, like saying that a glass is half (or more precisely, 0.592) full versus half (0.408) empty.

Šurán's leap day calendar and skip day calendar are mathematically equivalent; it's just that in the leap day calendar, the common years are 668 sols and the leap years are 669 sols, whereas in the skip day calendar, the common years are 669 sols and the skip years are 668 sols. He made the point that "the number of skip years is considerably lower than that of leap years." Well, yes, since 0.408 is considerably less than 0.592. He went through quite a lot of analysis to get to this point, which seems obvious. His intercalation rules for the two calendars are:

Leap years would be even years, save multiples of 160, with additional odd leap years after each multiple of 10 (i.e. 11, 21, 31, etc.).
Skip years would be even years, save multiples of 10, with the exception of multiples of 160 (i.e. 160, 320, 480, etc.) which would also be skip years.

In any case, in both his leap day calendar and his skip day calendar, in 160 years there are 65 668-sol years and 95 669-sol years.

Šurán's leap day and skip day calendars both consist of 23 four-week months and a three-week month, with blank sols (three or four, depending on the year), having no "day of the week", spread throughout the year. These calendars are perpetual, since each month contains an integral number of weeks, and thus they all begin on the same day of the week.

Next, Šurán considered a second set of intercalation rules involving a leap week calendar and a skip week calendar, in which an entire week is either periodically added to or removed from the calendar year:

Leap years would be even years, save multiples of 1100, with additional odd leap years after each multiple of 70 (i.e. 71, 141, 211. etc.).
Skip years would be even years, save multiples of 70, with additional odd skip years after each multiple of 1100 (i.e. 1101, 2201, 3301. etc.).

Again, there is no practical difference between these two calendars. In both his leap week calendar and his skip week calendar, in 7700 years there are 3747 665-sol years and 3953 672-sol years. Also, the leap day and skip day calendars both consist of 23 four-week months and a three-week month in a short year, while the long years contain 24 uniform months.

Šurán observed that:

Calendars with leap and skip week have maximum deviations to correct dates up to 10 days in absolute value (owing to intercalation or omission of a week). This apparent disadvantage is balanced by an uninterrupted continuity of weeks. If we consider that Mars' seasons (due to its significant orbital eccentricity of 0.093) vary in length up to (nearly) 27 days from their average value, this difference does not appear to be very large.

He picked the skip week calendar as being the best of the four:

The skip week calendar has the most uniform standard year, consisting of 24 equal months, two equal half-years and four equal quarter-years. It represents the best compromise for uniformity, accuracy and simplicity. Šurán mentioned several ideas regarding naming the 24 months:

Šurán presented several options for naming the Martian months. All involve variations on the Roman names on the Gregorian calendar, and grouping them into 12 pairs, as did Robinson:

A possible naming of Martian months, because Mars has two "moons", could be: January of Phobos, January of Deimos, etc., abbreviated to January P, January D, etc. Or, they could be January A, January B, etc.; eventually, the second month, or both, could have different endings (e.g. -ione, -yide; i.e. Januarione, Januaryide....

His names for the sols of the week were equally straightforward:

The Martian days could, likewise, have an ending different from Earth's names, e.g. -im (or -am, or -ah). Their names could be: Mondim, Tuesdim, etc. (or Mondam, Tuesdam, etc.; or Mondah, Tuesdah, etc.), distinguishing them thus from the days on Earth.

As the final detail, Šurán fixed the start of the calendar year as the beginning of winter in the Mars' northern hemisphere.

An HTML version of Šurán's paper, "A Calendar for Mars", is available on the Martian Time Web Site.

The first Martian calendar on the World Wide Web surfaced in April 1997. This one, devised by Frank N. Bauregger, was yet another stretched Gregorian calendar -- at least the fourth of its kind. His results agree very well with my own stretched Gregorian calendar. In the few cases where we differ, we have merely assigned a sol to one month rather than to an adjacent month. In Bauregger's method of intercalation, odd-numbered years contain 668 sols except for years ending in "5", which have 669 sols, as do all even-numbered years.

The chronology used at the Jet Propulsion Laboratory for the Pathfinder/Sojourner mission was similar to that used 21 years earlier for the Viking missions. The sol on which Pathfinder landed in Ares Vallis (Gregorian date: 4 July 1997) was designated "Sol 1".

Now, just because the unadorned numerical sequence of sols is still the norm at NASA and JPL doesn't stop some interplanetary navigators from having fun with the subject of Martian time. Anthony Taylor came up with a poem similar to D. G. Compton's, with the important difference that this one is astronomically correct:

Fifty-five sols hath September,
April, June, and November;
Fifty-six have all the rest,
Including February, subject to test:
Fifty-six sols comprise the norm,
But each fifth rev, three more's the form.

Also appearing on the World Wide Web after the arrival of Pathfinder on Mars was a calendar by Anders Ström. There were 12 months in Ström's calendar. Originally, Ström gave them the ordinary Gregorian names; however, the months that have 31 days on Earth had 56 sols on Mars, while those months whose normal compliment on Earth is 30 day had instead 55 sols on Mars. On Earth February has always gotten the short end of the stick, but had its day (er, sol) on Mars, where it contained 56 sols (one more in a leap year). The calendar year began at aphelion.

In 1998, Ström changed the names of the Martian months to reflect the constellations of the zodiac, beginning the year with Sagittarius on the vernal equinox. In Ström's second calendar, the months reflect to some degree the passage of the sun through the corresponding constellations. This relationship is not exact, however, since the months divide the year evenly, while the sun travels through the constellations more slowly near aphelion and more quickly near perihelion.

No intercalation sequence was provided for either calendar.

Ström's Martian clock consists of hours, minutes, and seconds of the normal terrestrial duration, with "an extra 37 minute period has been added at midnight."

William Woods' article "Options for Martian Timekeeping" makes its world debut on this web site.

Instead of settling on a specific solution for a clock, he entertains several options:

Twenty-four Mhours would obviously work very well, but 60 might work even better.

The Mhour need not be divided into 60x60 Msecs. Instead we could decimalize, dividing the Mhour into 1000 or 100x100 Msomethings.

Regarding the organization of a calendar, Woods also presents a number of fresh ideas:

Since the Myear is so long, it could plausibly be divided into six or eight seasons. Or even into five, if the long slow trip past aphelion seemed to justify having two northern-summer seasons.

Woods point out that such seasons would neither begin nor end on the equinoxes and solstices, but imagine the possibilities.... Two summers every year! Sounds like a Jan and Dean song!

Woods states that "each season should be divided into the same number of whole months, and each year should be a set of whole seasons." From these basic ideas, Woods outlines three methods of dividing the Martian year. The first scheme consists of 20 months of 33 or 34 sols, which could be grouped into either four seasons (each consisting of five months) or five seasons (each containing four months). His second option divides the year into 12 eight-week months, as Levitt did. In his third scheme, Woods divides the year into 24 four-week months, same as my Darian calendar. Woods notes that in the second and third options, the months could be grouped into four, six, or eight seasons. He further states that since the latter two options would total 672 sols (12 x 8 x 7 or 24 x 4 x 7), the excess sols could be subtracted from the last month in each quarter, or all from the last month of the year. Again, excising a sol from each quarter would agree with both and Levitt's work and mine.

With regard to naming the Martian months, Woods begins with the straightforward idea of extending the Roman scheme: ... , November, December, Undecember, Duodecember, .... As he points out, this sounds like a snap at first, but by the time you get to Quattuorvigintember, a lot of tongues are going to seize up. Alternatively, "naming them for constellations would do nicely," and Woods would add perizodiacal constellations to pad the list of the canonical dozen.

As far as setting the epoch of a Martian calendar, Woods points out that "putting the year 1 of the Martian Era in the recent past puts most of history on minus time." Woods feels that "for convenient conversion, 0.0 ME should be close to AD 0.0 (actually, 1.0 BC)." He fixes the autumnal equinox "in the first season of the year," noting that 1050.1 M.E. occurred nearly simultaneously with 1975.1 A.D.

Ultimately, Woods settles on a 24-month year, and at the end of his paper he provides two tables containing equivalent Earth dates and Mars dates. On this calendar, the autumnal equinox falls (no pun intended) on the 17th sol of the fourth month. A closer examination of these tables also shows that he settled on having a 27-sol month out of every six months, duplicating the arrangement of the Darian calendar. The dates in his tables are numeric, but since he favored using the constellations for naming the months, I have taken the liberty of adding twelve names to fill out the Woods calendar.

Woods made an excellent point regarding the terminology of equinoxes and solstices:

On Earth, it is natural to describe the equinoxes and solstices by the seasons in the northern hemisphere, since only a very small fraction of the land and population is in the south temperate zone. On Mars the situation is quite different so I suggest using southward, southern, northward, and northern in place of autumnal, winter, vernal, and summer.

The intercalation sequence devised by Woods is identical to Bauregger's: years divisible by two or five are long, while years ending in 1, 3, 7, or 9 are short. However, rather than have the variable sol occur at the end of a month that is not the last month of the year, Woods, like Levitt and myself, would have the variable sol at the end of the year. To provide additional accuracy, Woods specifies years divisible by 100 are short, except for those divisible by 500.

An HTML version of Wood's paper, "Options for Martian Timekeeping", is available on the Martian Time Web Site.

Also on the Martian Time Web Site is Pierre Hallet's delightful essay "The Fortieth of July", written in the style of Isaac Asimov. Hallet arrived at the same solutions as Levitt, but in this case, getting there is more than half the fun!

Two options for a Marian calendar are considered by Miguel Angel Serra Martín on the Calendario en Marte web site: a twelve-month version and a 24-month version. The first option applies the Latin names of the months on the Gregorian calendar, while the naming scheme on the 24-month calendar is still being defined. For both calendars, the winter solstice preceding the landing of the Soviet spacecraft Mars 3 was chosen for the epoch. Unfortunately, these calendars were based on the Martian sidereal day of 24 hours, 37 minutes, 22.66 seconds rather than the Martian solar day (sol) of 24 hours, 39 minutes, 35.2 seconds. While the error will probably be corrected in due course, it has led to the erroneous figure of 669.6011 sols per Martian year. Thus the intercalation scheme for both options calls for a 672-sol leap year in every five years. Serra Martín Option 1 contains eleven common months of 56 sols and an anomalous month of 53 sols, although in leap years, this last month also consists of 56 sols. Serra Martín Option 2 includes 23 common months of 28 sols and an anomalous month of 25 sols, except that in leap years, the anomalous month becomes a common month of 28 sols. Serra Martín observes that both 56 and 28 are divisible by seven, and thus the common months in the two calendar options contained an integral number of seven-sol weeks.

Regarding the Martian clock, like many other authors, William K. Hartmann stretches the familiar units of time in his novel Mars Underground. His character misquotes the length of the Martian year:

"Mars takes 670 sols, or Mars-days, to go around the sun."

The actual figure is 668.592 sols, so his calendar year is too long by one to two sols.

The Martian calendar is described as divided equally into twelve months, with the usual Roman names. Hartmann's character also states:

"Summer comes in June in the northern hemisphere, and so on. Here in the southern hemisphere, we have summer in late December on the day of the solstice, like Australia."

The exact date on which a solstice or equinox occurs is not mentioned, however.

"The two calendars are totally independent. A calendar is for the convenience of the people on the planet using it. A calendar is tailored to a planet. But we keep the number of the year the same as it is on Earth."

Hartmann appears to be trying to have it both ways here. How can the two calendars be "totally independent" if the number of the year on Mars is the same as it is on Earth, in spite of the fact that the length of the Martian year bears no resemblance to that of the terrestrial year? How would this be accomplished? Would a Martian year which began on 1 January be followed 355 sols (365 / 1.027) later by a year beginning on 20 July, followed by a year beginning on 41 January, followed by…? Or would a Martian year carry throughout the number of the Terran year in which the Martian year began, so that 54 December 2031 might be followed by 1 January 2033? Either way, when was last summer… 2030, or 2029? Will there be a "Summer of '42?"

"With a seven-day week, we can have a perpetual calendar if each month has eight weeks. Every month starts on Sunday."

Martian calendars that perpetuate the sloppiness of the Gregorian calendar are missing an opportunity. Social inertia has bogged down calendar reform on Earth, but on Mars we have a chance to make a number of important improvements. Possibly the example of a well-conceived Martian calendar will eventually be a catalyst for bringing about calendar reform on Earth. When Martian culture begins to influence Terran culture, that will be a significant milestone in human history.

"Holidays are celebrated according to the schedule on Earth, where they originated. So we have Christmas when it's December twenty-fifth on Earth, which falls at various times here. That way we get to share all our holidays on Earth."

Absolutely! Earth holidays according to Earth's calendar, and a Martian calendar for Martian holidays. Two totally independent systems.

Mickey Schmidt's calendar of 24 equal months is very similar to the Darian and Hollon calendars. The 27-sol months end with a six-sol week so that all months -- and all years -- can start on the first sol of the week. The main difference is in intercalation. Schmidt adds leap sols to two 27-sol months every five years. A third leap sol is inserted every 300 years, except in years divisible by 6,000. Schmidt favors new names for the sols of the week and the months, but does not propose any. He points out that new names for the sols will allow a single common sol of worship to be observed by all belief systems. Regarding month names:

They could reflect a future concept of a terra-formed Mars when there are plants and seasons. I personally like the month names the French tried to impose after the revolution like Blooming, Leafing, Fruiting etc. One could take month names from various cultures around the Earth and apply them to a part of the year which seems a likely match.

Schmidt mentions that "on the first day of Martian Spring the Sun enters Taurus". Actually, Sagittarius is the constellation of Martian vernal equinox. At this time, Mars is in Taurus as seen from the sun, which is why Zubrin begins his calendar with the month of Taurus.

Schmidt considers several options for the Martian clock, including the ubiquitous "Martian stretched" 24-60-60 scheme. Also discussed is a 20-50-100 option, as well as the idea of retaining the standard second and trying to fashion some sort of Martian clock around it. He concludes:

Of the three, the second option would be very useful but I suspect the first option will be chosen because all you need to keep track of time on Mars is a slow clock to keep time.

For coordination between scientific users between Earth and Mars the International defined second would be used for calibrating equipment relating to communications standards etc but for common time on Mars a new second should be adapted.

An HTML version of Schmidt's ideas is available on the Martian Time Web Site.

1998: THE SHERWOOD CALENDARS

Anton Sherwood devised four 24-month calendars. All options begin on the Martian vernal equinox. Although he doesn't assign specific names to the months, he suggests naming each month for the brightest star, weighted by the cosine of the declination, that crosses the midnight line in that month.

Option A is based on equal arcs of 15 degrees, with months having a fractional number of sols larger than .43 rounded up, and those with a smaller fraction rounded down. The 11th month contains an extra sol in three years out of five.

In Option B, in order to make the months slightly more equal in length, the longer months are rounded down, the shorter months rounded up. The leap sol comes at the end of the 12th month.

In Option C, the four shortest months (the 15th through the 18th) are assigned 27 sols, while the rest have 28 sols. The leap sol is assigned to the 18th month.

In Option D, each month be assigned its "true" number of sols, rounded either up or down as in Options A and B, but with the further rule that wherever possible adjacent months differ in length by no more than one sol.

An HTML version of Sherwood's ideas is available on the Martian Time Web Site. An e-mail discussion between Anton Sherwood and Pierre Hallet is available at http://www.jps.net/antons/Mars.txt.

1998: THE HENSEL MONTH NAMES AND HENSEL CLOCK

Alan Hensel found the names of the months on the Darian calendar difficult to remember in sequence, and proposed an alternate scheme that names the months in a similar way to Earth's September through December. Numbering all the way to 24 would be a bit of a nightmare, so instead, each quarter is numbered separately, with a different suffix that is chosen according to the season with which the quarter mostly coincides. There are six months per quarter, so the numbering is only from one to six, leaving no overlap with the Gregorian names, which start at seven (September).

To demonstrate, Hensel offered the following example:

Vernalis, Duvernalis, Trivernalis, Quadrivernalis, Pentavernalis, Hexavernalis
Aestas, Duestas, Triestas, Quadrestas, Pentestas, Hexestas
Autumnus, Duautumn, Triautumn, Quadrautumn, Pentautumn, Hexautumn
Unember, Duember, Triember, Quadrember, Pentember, Hexember

The Greek "Pent-" is used instead of the Latin "Quint-" so that the months can be abbreviated unambiguously with 2 letters (it also sounds better). And the choice of the Greek "Hex-" instead of the Latin "Sex-" is clear: if there are gonna be "sex" months, they shouldn't be the shortest months of the year!

Hensel also devised a clock which he described as "semi-metric". He observes that a 24-hour sol is to be preferred over a 10-hour clock since it conveniently divides into three 8-hour shifts. However, each hour is divided into ten units, which are in turn divided into a thousand secondary units. Thus the clock display is formatted as hh:m:sss, (although Hensel stresses that the primary and secondary divisions of the hour should be called something other than minutes and seconds, since he proposes no new unit names, he still refers to minutes and seconds). Hensel's second is about one-third the duration of a standard second, which is about a quickly as a person can count, and is also about as fast a digital display as one can observe without it becoming an incomprehensible blur. Hensel's minute is about 6 minutes 10 seconds of terrestrial time, and he notes that this is a convenient unit for civil use since people usually refer to the time of day to the nearest five minutes. He further states that a 24:10:1000 system avoids any possible confusion with terrestrial time. "12:5" is clearly distinguishable from an Earth time (such as "12:30"), which is basically the same argument usually given for not naming Martian months January, February, March, et cetera. One is also not quite as tempted to call the smallest units "seconds", which would cause confusion with the SI unit that would naturally still be used among scientists on Mars. On Earth, 4:10 could mean either 4 hours 10 minutes, or 4 minutes 10 seconds, but with the Hensel clock, one can clearly distinguish the context by number of digits in each field. And of course, it is easier to add and subtract time intervals in base 10 than in base 60.

1998: THE HOLLON CALENDAR

Bill Hollon, who has made a very thorough study of the subject of calendrics, devised a Martian calendar on contract to Leonard Bromberg. The structure of the Hollon calendar is similar to the Darian calendar in that is consists of 24 months containing 27 to 28 sols. He points out the importance of dividing the Martian year into eighths, as these are analogous to quarters of the terrestrial years. Also, he begins his calendar year on the Martian vernal equinox.

Hollon disregards the need for a leap year rule. This ignores the trend in calendrics over the past 2000 years. For instance, the Hebrew calendar was once observation-based, but has evolved into a rule-based calendar. The advantages of a rule-based calendar in calculating the number of days between two dates, or in converting dates between two different calendar systems, should be obvious.

Hollon recognizes the need for different naming conventions for the Martian sols of the week and months, a point that has been overlooked by several other authors. His names for the seven sols of the week are: Sunday, Phobosday, Deimosday, Earthday, Venusday, Jupiterday, and Saturnday. His months are named in alphabetical order "to honor individuals who either participated in early space exploration or who contributed to mankind’s understanding of science." He mentions that the 24 months run from Aldrin to Zubrin, with two of the 26 letters of the alphabet omitted. The names of the other months are not specified, however. An advantage of this system is that "a fairly good idea of each month’s location in the year can be had by envisioning where the first letter on its names fits within the alphabet."

As with Hollon's terrestrial Fixed-Week calendar, his Martian calendar is also a fixed-week design, making it nearly identical in structure to the Darian calendar.

Hollon provides no epoch for his calendar.

An HTML version of Hollon's paper, "Rationale for the Martian Calendar’s Structure", is available on the Martian Time Web Site.

To my knowledge, the Millennium Mars Calendar developed by James M. Graham and Kandis Elliot is the first mass-produced Martian calendar. The calendar displays both Martian and terrestrial dates.

The Millennium Mars Calendar contains 20 months named for Greek gods, which gives it a nice classical flavor. The year is divided into equal quarters in which the first three months have 33 sols and the remaining two have 34 sols. Since neither of these numbers is divisible by seven, month begin on varying days of the week.

The epoch for the calendar is 24 December 1975, intended as the Martian vernal equinox prior to the Viking 1 landing. Curiously, although Graham arrived at this date by a different set of calculations, he came up with the same error that I originally did, and unfortunately, when he came across my original paper, "Martian Standard Time", it confirmed his erroneous results. No doubt this six-day error will be corrected in the next edition.

Meanwhile, Elliot's artwork is a real treat, which alone makes the calendar worth having. Some of her artwork can be seen on the Millennium Mars web site.

Frans Blok's Rotterdam Month Naming System provides another alternative to the month names on the Darian calendar.

He deftly skirts the problem of cultural bias by inventing new, artificial names. In doing so, Blok gives "a nice push forward for Martian culture; now that almost everything on Mars has been named after places or people from earth, it's time to invent some new names." A prime consideration in designing these names was pronounceability, regardless of one's native language, so most consonants are singlular, while only a few are doubled. The result is a set of very esthetic names with a touch of the alien, and which are reminiscent of the names and words that Edgar Rice Burroughs invented for Barsoom.

The 24 month names are arranged in alphabetical order. They also have several mathematical relationships designed into them. First of all, Blok constructed rules to reflect the variable orbital velocity of Mars in the length of the names. As he observes:

You don't even have to know the order of the months by heart to realize that a short name must be a spring month. The rule of thumb for future generations of Martian schoolchildren will be "the names are fast when Mars is slow". The first seven months (spring in the north, fall in the south) have four characters and two syllables, numbers 8 thru 13 (summer/winter) as well as 19 thru 24 (winter/summer) count six characters and three syllables and months 14 thru 18 (fall/spring) have eight letters and four syllables.

Other mathematical patterns reflect the many factors contained in the number 24. The letters of the mnemonic word "ranilo" are used as endings for each of the six months in a quarter. This scheme also results in odd-numbered month ending in consonants and even-numbered months ending in vowels. Next, every fourth month contains a "D". Finally, all of the northern hemisphere's autumn and winter months contain a "U".

An HTML version of Blok's paper, "The Rotterdam Month Naming System", is available on the Martian Time Web Site.

A number of realtime Martian clock applets written in the Java programming language appeared on the World Wide Web in 1997, in addition to the one located on this web site. All of these clocks are based on stretched hours, minutes, and seconds.

The clock devised by Michael D. Allison and Robert B. Schmunck which appears on the Goddard Institute's web site displays a cylindrical map of Mars, showing the day/night terminator. The Viking 1, Viking 2, and Pathfinder landing sites are also shown. Earth time is in Unversal Time, Coordinated (UTC). The user can select any point on Mars and get a readout of two types of Martian time: local mean solar time (LMST) and local true solar time (LTST). The date on Mars is not displayed.

Randall S. Bohn's clock is a text-only display showing LTST at the Pathfinder site. The date on Mars is expressed in sols since the Pathfinder landing. Earth time and date is not displayed.

Joseph Knapp's clock is capable of displaying the time on Mars at the landing sites of several spacecraft. The date on Mars is expressed in sols since the Pathfinder landing. Earth date and time is displayed in terms of Pacific time (Time Zone 8). The position of Mars in terms of both Earth coordinates and Sun coordinates is also displayed. A row of buttons allows the user to go forward or backward in time, or return to the present.

James Scarborough's clock displays the time and date (sols since landing) at the Pathfinder site. The time of sol is displayed in both digital and analog formats. Earth time and date is not displayed.

Frank Sorenson's clock is a text-only display of Pacific Time on Earth but no date, and the time and date (sols since landing) at the Pathfinder site.

My original Java code for an Earth-Mars clock was cleaned up considerably by Alan Hensel. It is a text-only display of Universal Time (Coordinated) and Gregorian date on Earth, and Levitt Mean Time (prime meridian time) and Darian date on Mars. It is calibrated to the Allison-Schmunck Clock. A variant of the Gangale clock displays not only the time and date on Earth and Mars, but on Io, Europa, Ganymede, and Callisto as well.

I also adapted the Java code to display decimal time as developed by Bruce A. Mackenzie.

Meanwhile, Alan adapted the base code to implement his Martian Semi-Metric Clock descibed above.

Jeff Roche's clock is a text-only display set to local time at the Pathfinder site.

David Gatwood's clock is a text-only display, but does not update in real time. Instead, the clock updates when the HTML file is reloaded.

Few things are more taken for granted during the course of a workday than the act of glancing at a watch or of referring to a calendar. These artifacts are commonplaces in our culture, and yet consider how indispensable these mundane instruments are to the harmonious functioning of a complex civilization. Nearly every field of endeavor in our fast-paced urban society depends on the ability to manage time effectively. The timepiece rules supreme; it is a mandatory badge that identifies each of us as a participant in the activities of the modern world. Chronometers are our passports through today; calendars our roadmaps into next week and next year.

Our species is on the verge of reaching across the gulf of space to establish permanent residence on other planets of the solar System. The chronometric implements of our society, so ubiquitous on Earth, are among the necessary accoutrements that we must take with us. On Mars, as on no other planet in the solar System, colonists will find it essential to express the order of events in their lives in terms of the natural cycles of their new environment: a time to awaken, a time to sleep; a time to sow, a time to reap.

If the spacefaring nations of Earth are to go to the trouble of establishing a standardized system for Mars (which they ultimately must do), they might as well take into account at the outset not only the chronometric needs of the robotic missions of the 1990s, but also those of the human settlementsthat will follow. It is true that there will be no system requirement to adopt a Martian calendar for future unmanned Mars missions; the practice established during the Viking program (and now being repeated on the Pathfinder mission) of keeping track of Martian solar days as a simple numerical sequence could be repeated. However, while the counting off of a sterile sequence of sols is perfectly suitable for operating robots on the surface of Mars, it is completely devoid of any human appeal -- it is flavorless and colorless.

The enterprise of sending human expeditions to Mars and of permanently settling that planet will obviously require broad political support among many nations and sustained over several decades. I believe that the immediate institution of a Martian calendar might serve a significant political and social purpose as a symbol of the human commitment to establish a permanent presence on that new world in the coming decades. Mars will become more of a human place in the public imagination as familiar human references are adapted for that planet. The realization will become more widespread that the concept of colonies on Mars is transitioning from the realm of science fiction to that of imminent accomplishment. Although much engineering development remains to be done before the first manned landing can be achieved, the process of humanizing Mars and laying the foundation for a new civilization can and should begin now. The early promulgation of a human-oriented Martian calendar, starting with the next unmanned Martian surface operations, can be a symbol of a spreading awareness that human beings will not be going to Mars merely as visitors, but that we are going there with every intention of staying, putting down our roots, and flourishing on that new world.

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