The Darian calendar is a proposed system of

timekeeping Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compa ...

designed to serve the needs of any possible future human settlers on the planet

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. It was created by

aerospace engineer Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is s ...

political scientist Political science is the scientific study of politics. It is a social science dealing with systems of governance and Power (social and political), power, and the analysis of political activities, political philosophy, political thought, polit ...

, and space jurist Thomas Gangale in 1985 and named by him after his son Darius. It was first published in June 1986. In 1998 at the founding convention of the

Mars Society The Mars Society is a nonprofit organization that advocates for human exploration and colonization of Mars. It was founded by Robert Zubrin in 1998 and its principles are based on Zubrin's Mars Direct philosophy, which aims to make human miss ...

the calendar was presented as one of two calendar options to be considered along with eighteen other factors to consider for the

colonization of Mars 475px, Map of the year each country achieved List of sovereign states by date of formation, independence. Colonization (British English: colonisation) is a process of establishing occupation of or control over foreign territories or peoples f ...

. Due to the use of 28 sol months, the Darian calendar has no mechanism for synchronization with Earth dates or with synodic periods.

Year length and intercalation

The basic time periods from which the calendar is constructed are the Martian

solar day A synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time. The synodic day is distinguished from the sidereal day, which is ...

(sometimes called a sol) and the Martian vernal equinox year. The sol is 39 minutes 35.244 seconds longer than the Terrestrial solar day, and the Martian vernal equinox year is 668.5907 sols in length (which corresponds to 686.9711 days on Earth). The basic intercalation formula therefore allocates six 669-sol years and four 668-sol years to each Martian decade. The former are still called

leap years A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) compared to a common year. The 366th day (or 13th month) is added to keep ...

, even though they are more common than non-leap years, and are years that are either odd (not evenly divisible by 2) or are evenly divisible by 10: this produces 6,686 sols per ten years, giving an average year of 668.6 sols. A 1998 iteration of the Darian calendar had leap years cancelled if the year was divisible by 100, unless the year was also divisible by 500; adding these rules produces an average year of 668.592 sols, a more reasonable approximation. However, these static intercalation schemes did not take into account the slowly increasing length of the Martian vernal equinox year. Thus, in 2006, Gangale devised a series of intercalation formulas, all of which have in common the basic decennial cycle, as shown in the following table: This extended intercalation scheme gives an average year of 668.59453 days over a 10,000-year period: this results in an error of only about one sol at the end of 12,000 Martian years, or the year 24,180 of the

Common Era Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the ...

Calendar layout

The year is divided into 24

month A month is a unit of time, used with calendars, that is approximately as long as a natural phase cycle of the Moon; the words ''month'' and ''Moon'' are cognates. The traditional concept of months arose with the cycle of Moon phases; such lunar mo ...

s. The first 5 months in each quarter have 28 sols, while the final month has 27 sols unless it is the final month of a leap year, when it contains the leap sol as its final sol. The calendar maintains a seven-sol

week A week is a unit of time equal to seven days. It is the standard time period used for short cycles of days in most parts of the world. The days are often used to indicate common work days and rest days, as well as days of worship. Weeks are ofte ...

, but the week is restarted from its first sol at the start of each month. If a month has 27 sols, this causes the final sol of the week to be omitted. This is partly for tidiness and can also be rationalised as making the average length of the Martian week close to the average length of the Terrestrial week; 28 Earth days is very close to Martian sols, whereas a month is an average length of Martian sols. In the table, the sols of the week are Sol Solis, Sol Lunae, Sol Martis, Sol Mercurii, Sol Jovis, Sol Veneris, Sol Saturni. The last sol of Vrishika is an intercalary sol that only occurs on leap years, like February 29 in the Gregorian calendar.

Start of year

The Martian year is treated as beginning near the

equinox A solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun appears to rise directly east and set directly west. This occurs twice each year, arou ...

marking spring in the northern hemisphere of the planet. Mars currently has an axial inclination similar to that of the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, so the Martian seasons are perceptible, though the greater

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of Mars' orbit about the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

compared with that of the Earth means that their significance is strongly amplified in the southern hemisphere and masked in the northern hemisphere.

Epoch

Gangale originally chose late 1975 as the

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

of the calendar in recognition of the American

Viking program The ''Viking'' program consisted of a pair of identical American space probes, ''Viking 1'' and ''Viking 2'' both launched in 1975, and landed on Mars in 1976. The mission effort began in 1968 and was managed by the NASA Langley Research Cent ...

as the first fully successful ( American) soft landing mission to Mars (the earlier 1971

Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

Mars 3 Mars 3 was a robotic space probe of the Soviet Mars program, launched May 28, 1971, nine days after its twin spacecraft Mars 2. The probes were identical robotic spacecraft launched by Proton-K rockets with a Blok D upper stage, each consisti ...

Landing having delivered only 15 seconds of data from the planet's surface). In 2002 he adopted the Telescopic Epoch, first suggested by Peter Kokh in 1999 and adopted by Shaun Moss in 2001 for his ''Utopian Calendar'', which is in 1609 in recognition of

Johannes Kepler Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, Natural philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best know ...

's use of

Tycho Brahe Tycho Brahe ( ; ; born Tyge Ottesen Brahe, ; 14 December 154624 October 1601), generally called Tycho for short, was a Danish astronomer of the Renaissance, known for his comprehensive and unprecedentedly accurate astronomical observations. He ...

's observations of Mars to elucidate the laws of planetary motion, and also

Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

's first observations of Mars with a

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. Selection of the Telescopic Epoch thus unified the structures of the Darian and Utopian calendars, their remaining differences being nomenclatural. It also avoids the problem of the many telescopic observations of Mars over the past 400 years being relegated to negative dates.

Nomenclature

The Darian calendar has been widely imitated. Suggested variations abound on the internet that use different nomenclature schemata for the days of the week and the months of the year. In the original Darian calendar, the names of the 24 months were provisionally chosen by Gangale as the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

names of

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

s of the

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the Sun across the celestial sphere over the course of the year. Within this zodiac ...

and their

Sanskrit Sanskrit (; stem form ; nominal singular , ,) is a classical language belonging to the Indo-Aryan languages, Indo-Aryan branch of the Indo-European languages. It arose in northwest South Asia after its predecessor languages had Trans-cultural ...

equivalents in alternation. The 7 sols of the week, similarly, were provisionally named after the Sun, the largest Martian moon Phobos (Sol Phobotis) and the 5 brightest planets as seen from Mars including Earth (Sol Terrae). These were later modified to follow the familiar convention of the Romance languages, replacing Sol Phobotis with Sol Lunae and Sol Terrae with Sol Martis. The ''Darian Defrost Calendar'', however, uses the ''Rotterdam System'' to create new names for the Martian months out of patterns relating letter choice and name length to month order and season. The ''Utopian Calendar'', devised by the Mars Time Group in 2001, also has additional suggestions for nomenclature modification. In 2025, Gangale adapted the Chinese solar terms as alternative names of the months to accommodate East Asian cultures, observing, "they invoke events which may occur with the passing of the seasons on Mars someday if terraforming is successful; thus, the Darian Chinese system is both aspirational and inspiring."

Mars Julian sol

The Mars Julian sol count is analogous to the Julian Day count on Earth, in that it is a continuous numerical counting of days from an epoch. The Mars Julian sol epoch is the same as for the Darian calendar, thus Mars Julian sol 0 is 1 Sagittarius 0.

Comparison with timekeeping systems in planetary science

Since the Darian calendar is designed as a civil calendar for human communities on Mars, it has no precise analog in the scientific community, which has no need to mark Martian time in terms of weeks or months. Two unrelated epochs that have gained some traction in the scientific community are the Mars sol date and the Mars year. In 1998 Michael Allison proposed the Mars sol date epoch of 29 December 1873 (Julian Day 2405521.502). In 2000 R. T. Clancy ''et al.'' proposed the Mars year 1 set to the epoch 11 April 1955 (Julian Day 2435208.456). The Clancy Mars year is reckoned from one Martian northward equinox to the next (L_s = 0°), and specific dates within a given year are expressed in L_s. The Clancy Mars year count is approximately equal to the Darian year count minus 183. The Allison Mars sol date epoch equates to L_s = 276.6° in a year that is undefined in the Clancy Mars year count. It converts to 25 Virgo 140 on the Darian calendar and Mars Julian sol 94128.511.

Martiana calendar

In 2002 Gangale devised a variant of the Darian calendar that reconciles the months and the sols of the week in a repeating pattern and removes the need to omit days of the week. In the Martiana variant, all the months in a given quarter begin on the same sol of the week, but the sol that begins each month shifts from one quarter to the next, based on the scheme devised by the

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

Robert G. Aitken in 1936. The following table shows the sol of the week on which each month in the quarter begins. The first quarter corresponds to spring in the Martian northern hemisphere and autumn in the Martian southern hemisphere. The leap sol occurs at the end of odd-numbered years as in the original Darian calendar. Since the last month of odd-numbered years contains 28 sols, the following year also begins on Sol Solis, resulting in a two-year cycle over which the relationship of the sols of the week to the months repeats. The sol that is added every tenth year is epagomenal (not counted as part of the week), thus the two-year rotation of the sols of the week is not disrupted. The Martiana scheme avoids the Darian calendar's need to shorten the week to six sols three to four times per year. The disadvantage is that the scheme results in a two-year cycle for reconciling the sols of the week and the months, whereas the Darian calendar is repeatable from month to month.

Other Darian calendars

In 1998 Gangale adapted the Darian calendar for use on the four

Galilean Generically, a Galilean (; ; ; ) is a term that was used in classical sources to describe the inhabitants of Galilee, an area of northern Israel and southern Lebanon that extends from the northern coastal plain in the west to the Sea of Galile ...

moons of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

discovered by Galileo in 1610: Io, Europa, Ganymede, and

Callisto CALLISTO (''Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations'') is a reusable VTVL Prototype, demonstrator propelled by a small 40 kN Japanese LOX-LH2 rocket engine. It is being developed jointly by the CNES, French ...

. In 2003 he created a variant of the calendar for

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

Important dates in Martian history

*Mars dates are approximate where the exact (Earth) time of the event is not stated.

The Darian calendar in fiction

Gangale was inspired to create the calendar after reading ''Red Planet'', a 1949 science fiction book by

Robert A. Heinlein Robert Anson Heinlein ( ; July 7, 1907 – May 8, 1988) was an American science fiction author, aeronautical engineer, and naval officer. Sometimes called the "dean of science fiction writers", he was among the first to emphasize scientific acc ...

. In the book, Heinlein postulates a 24-month Martian calendar.Jan Gyllenbok, ''Encyclopaedia of Historical Metrology, Weights, and Measures'', volume 1, p. 284, Birkhäuser, 2018 . The Darian calendar is mentioned in several works of fiction set on Mars: * ''Star Trek: Department of Temporal Investigations: Watching the Clock'' by Christopher L. Bennett, Pocket Books/Star Trek (April 26, 2011) * '' The Quantum Thief'' by Hannu Rajaniemi, Tor Books; Reprint edition (May 10, 2011) * '' Thin Air'' by Richard K. Morgan, Del Rey Books, October 2018. * ''Black Helicopters'' by Caitlín R. Kiernan, Tor Books, 2018

Notes

References

* Bennett, Christopher L. (2011-04-26). Star Trek: Department of Temporal Investigations: Watching the Clock, p. 352. Pocket Books/Star Trek. * Gangale, Thomas. (1986-06-01). "Martian Standard Time". ''Journal of the British Interplanetary Society.'' Vol. 39, No. 6, p. 282–288 * Gangale, Thomas. (1997-02-01). "Mare Chronium: A Brief History of Martian Time". American Astronautical Society. AAS 90–287. ''The Case for Mars IV: The International Exploration of Mars.'' Ed. Thomas R. Meyer. San Diego, California. Univelt, Incorporated. * Gangale, Thomas. (1998-08-01). "The Darian Calendar". Mars Society. MAR 98-095. ''Proceedings of the Founding Convention of the Mars Society.'' Volume III. Ed. Robert M. Zubrin, Maggie Zubrin. San Diego, California. Univelt, Incorporated. 13-Aug-1998. * Gangale, Thomas, and Dudley-Rowley, Marilyn. (2004-07-01). "The Architecture of Time: Design Implications for Extended Space Missions" Society of Automotive Engineers. SAE 2004-01-2533. ''SAE Transactions: Journal of Aerospace.'' * Gangale, Thomas, and Dudley-Rowley, Marilyn. (2005-12-01). "Issues and Options for a Martian Calendar". ''Planetary and Space Science.'' Vol. 53, pp. 1483–1495. * Gangale, Thomas. (2006-07-01). "The Architecture of Time, Part 2: The Darian System for Mars." Society of Automotive Engineers. SAE 2006-01-2249. * Rajaniemi, Hannu. The Quantum Thief, Ch, 12. Tor Books. * Sakers, Don. (2004-01-01). The Sf Book of Days, pp. 7, 19, 31, 53, 81, 103, 113, 123, 135, 145–149. Speed-Of-C Productions. * Smith, Arthur E. (1989-01-01). Mars: The Next Step, p. 7. Taylor & Francis.

External links

*
The Darian System
Retrieved 1 Dec 2015.

Apps

* iPhone/iPad

Arkane Systems * Perl
Date-Darian-Mars 0.003
Andrew Main * Ruby
Darian Mars calendar converter
Andrey Sitnik
Martian Calendar
Laurie Harrison
Mars Weather Dashboard Widget
MobiliseMe * Android
Mars Sky
xeronaut.com
Mars calendar and clock in your browser
Interplanetary Immigration Center {{DEFAULTSORT:Darian Calendar 1985 works Mars Proposed calendars Specific calendars 1986 introductions