Though no standard exists, numerous calendars and other
timekeeping
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to co ...
approaches have been proposed for the planet Mars. The most commonly seen in the scientific literature denotes the time of year as the number of degrees from the northern vernal equinox, and increasingly there is use of numbering the Martian years beginning at the equinox that occurred April 11, 1955.).
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
has an
axial tilt
In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbi ...
and a rotation period similar to those of
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
. Thus, it experiences seasons of
spring
Spring(s) may refer to:
Common uses
* Spring (season)
Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...
,
summer
Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, the earliest sunrise and latest sunset occurs, daylight hours are longest and dark hours are shortest, wit ...
,
autumn
Autumn, also known as fall in American English and Canadian English, is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September ( Northern Hemisphere) or March ( Sou ...
and
winter
Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures ...
much like Earth. A sol, or Martian day, is less than an hour longer than an Earth day. A Mars year is almost twice as long as Earth's, though its
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...
is considerably larger, which causes those seasons to vary significantly in length.
Sols
The average length of a Martian
sidereal day
Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coord ...
is (88,642.663 seconds based on SI units), and the length of its
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 ...
is (88,775.244 seconds). The corresponding values for Earth are currently and , respectively, which yields a conversion factor of Earth days/sol: thus, Mars's solar day is only about 2.75% longer than Earth's.
The term " sol" is used by
planetary scientists
Planetary means relating to a planet or planets. It can also refer to:
;Science
* Planetary habitability, the measure of an astronomical body's potential to develop and sustain life
* Planetary nebula, an astronomical object
;People
* Planetary ...
to refer to the duration of a solar day on Mars. The term was adopted during NASA's
Viking
Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden),
who from the late 8th to the late 11th centuries raided, pirated, traded and se ...
project (1976) in order to avoid confusion with an Earth "day". By inference, Mars' "solar hour" is of a sol (1 hr 1 min 39 sec), a "solar minute" of a solar hour (61.65 sec), and a "solar second" of a solar minute (1.0275 sec).
Mars Sol Date
When accounting solar days on Earth, astronomers often use
Julian date
The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date).
...
s—a simple sequential count of days—for timekeeping purposes. An analogous system for Mars has been proposed " r historical utility with respect to the Earth-based atmospheric, visual mapping, and polar-cap observations of Mars..., a sequential count of sol-numbers". This Mars Sol Date (MSD) starts "prior to the 1877 perihelic opposition." Thus, the MSD is a running count of sols since 29 December 1873 (coincidentally the birth date of astronomer
Carl Otto Lampland
Carl Otto Lampland (December 29, 1873 – December 14, 1951) was an American astronomer. He was involved with both of the Lowell Observatory solar system projects, observations of the planet Mars and the search for Planet X.
Biography ...
). Numerically, the Mars Sol Date is defined as MSD = (Julian Date using
International Atomic Time
International Atomic Time (abbreviated TAI, from its French name ) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid. TAI is a weighted average of the time kept by over 450 atomic ...
- 2451549.5 + ''k'')/1.02749125 + 44796.0, where ''k'' is a small correction of approximately d (or 21.6 s) due to uncertainty in the exact geographical position of the prime meridian at Airy-0 crater.
Time of day
A convention used by spacecraft lander projects to date has been to enumerate local solar time using a 24-hour "Mars clock" on which the hours, minutes and seconds are 2.75% longer than their standard (Earth) durations.
This has the advantage that no handling of times greater 23:59 is needed, so standard tools can be used. The Mars time of noon is 12:00 which is in Earth time 12 hours and 20 minutes after midnight.
For the
Mars Pathfinder
''Mars Pathfinder'' (''MESUR Pathfinder'') is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight, wheeled robot ...
,
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...
(MER),
Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
, and
Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
missions, the operations teams have worked on "Mars time", with a work schedule synchronized to the local time at the landing site on Mars, rather than the Earth day. This results in the crew's schedule sliding approximately 40 minutes later in Earth time each day. Wristwatches calibrated in Martian time, rather than Earth time, were used by many of the MER team members.
Local solar time has a significant impact on planning the daily activities of Mars landers. Daylight is needed for the
solar panels
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a phot ...
of landed
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
. Its
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
rises and falls rapidly at sunrise and sunset because Mars does not have Earth's thick atmosphere and oceans that soften such fluctuations. Consensus has recently been gained in the scientific community studying Mars to similarly define Martian local hours as 1/24th of a Mars day.
As on Earth, on Mars there is also an
equation of time
In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in ...
that represents the difference between sundial time and uniform (clock) time. The equation of time is illustrated by an
analemma
In astronomy, an analemma (; ) is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble a figure ei ...
. Because of
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...
, the length of the solar day is not quite constant. Because its orbital eccentricity is greater than that of Earth, the length of day varies from the average by a greater amount than that of Earth, and hence its equation of time shows greater variation than that of Earth: on Mars, the Sun can run 50 minutes slower or 40 minutes faster than a Martian clock (on Earth, the corresponding figures are slower and faster).
Mars has a
prime meridian
A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great c ...
, defined as passing through the small crater
Airy-0
Airy-0 is a crater inside the larger Airy Crater on Mars, whose location defined the position of the prime meridian of that planet. It is about 0.5 km (0.3 mile) across and lies within the dark region Sinus Meridiani, one of the early a ...
. The prime meridian was first proposed by German astronomers
Wilhelm Beer
Wilhelm Wolff Beer (4 January 1797 – 27 March 1850) was a banker and astronomer from Berlin, Prussia, and the brother of Giacomo Meyerbeer.
Astronomy
Beer's fame derives from his hobby, astronomy. He built a private observatory with a ...
and
Johann Heinrich Mädler
Johann, typically a male given name, is the German form of ''Iohannes'', which is the Latin form of the Greek name ''Iōánnēs'' (), itself derived from Hebrew name ''Yochanan'' () in turn from its extended form (), meaning "Yahweh is Gracious" ...
in 1830 as marked by the fork in the
albedo feature
An albedo feature is a large area on the surface of a planet (or other Solar System body) which shows a contrast in brightness or darkness (albedo) with adjacent areas.
Historically, albedo features were the first (and usually only) features to b ...
Giovanni Schiaparelli
Giovanni Virginio Schiaparelli ( , also , ; 14 March 1835 – 4 July 1910) was an Italian astronomer and science historian.
Biography
He studied at the University of Turin, graduating in 1854, and later did research at Berlin Observatory, ...
. This convention was readily adopted by the astronomical community, the result being that Mars had a universally accepted prime meridian half a century before the
International Meridian Conference
The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of U.S. President Chester A. ...
of 1884 established one for Earth. The definition of the Martian prime meridian has since been refined on the basis of spacecraft imagery as the center of the crater
Airy-0
Airy-0 is a crater inside the larger Airy Crater on Mars, whose location defined the position of the prime meridian of that planet. It is about 0.5 km (0.3 mile) across and lies within the dark region Sinus Meridiani, one of the early a ...
in Terra Meridiani.
However, Mars does not have
time zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s defined at regular intervals from the prime meridian, as on Earth. Each lander so far has used an approximation of local solar time as its frame of reference, as cities did on Earth before the introduction of
standard time
Standard time is the synchronisation of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the r ...
in the 19th century. (The two
Mars Exploration Rovers
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit'' and ''Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rovers to explore the Martian surface and ...
happen to be approximately 12 hours and one minute apart.)
Since the late 1990s and arrival of
Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...
at Mars, the most widely used system for specifying locations on Mars has been planetocentric coordinates, which measure longitude 0°–360° East and latitude angles from the center of Mars. An alternative system that was used before then is planetographic coordinates, which measure longitudes as 0°–360° West and determined latitudes as mapped onto the surface. However, planetographic coordinates remain in use, such as on the
MAVEN
MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of
the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...
orbiter project.
Coordinated Mars Time
Coordinated Mars Time (MTC) or Martian Coordinated Time is a proposed Mars analog to Universal Time (
UT1
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with ...
) on Earth. It is defined as the mean solar time at Mars's prime meridian. The name "MTC" is intended to parallel the Terran
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used ...
(UTC), but this is somewhat misleading: what distinguishes UTC from other forms of UT is its
leap second
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observe ...
s, but MTC does not use any such scheme. MTC is more closely analogous to
UT1
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with ...
.
Use of the term "Martian Coordinated Time" as a planetary standard time first appeared in a journal article in 2000. The abbreviation "MTC" was used in some versions of the related Mars24 sunclock coded by the NASA
Goddard Institute for Space Studies
The Goddard Institute for Space Studies (GISS) is a laboratory in the Earth Sciences Division of NASA's Goddard Space Flight Center affiliated with the Columbia University Earth Institute.
The institute is located at Columbia University in Ne ...
. That application has also denoted the standard time as "Airy Mean Time" (AMT), in analogy of
Greenwich Mean Time
Greenwich Mean Time (GMT) is the Local mean time, mean solar time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, i ...
(GMT). In an astronomical context, "GMT" is a deprecated name for Universal Time, or sometimes more specifically for UT1.
Neither AMT or MTC has yet been employed in mission timekeeping. This is partially attributable to uncertainty regarding the position of Airy-0 (relative to other longitudes), which meant that AMT could not be realized as accurately as local time at points being studied. At the start of the
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...
missions, the positional uncertainty of Airy-0 corresponded to roughly a 20-second uncertainty in realizing AMT. In order to refine the location of the prime meridian, it has been proposed that it be based on a specification that the Viking Lander 1 is located at 47.95137°W.
Lander mission clocks
When a NASA spacecraft lander begins operations on Mars, the passing Martian days (sols) are tracked using a simple numerical count. The two
Viking
Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden),
who from the late 8th to the late 11th centuries raided, pirated, traded and se ...
Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
rover ''Curiosity'', ''
InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
'', and Mars 2020 ''Perseverance'' missions all count the sol on which the lander touched down as "Sol 0". Mars ''Pathfinder'' and the two Mars Exploration Rovers instead defined touchdown as "Sol 1".
Each successful lander mission so far has used its own "time zone", corresponding to some defined version of local solar time at the landing site location. Of the nine successful NASA Mars landers to date, eight employed offsets from local mean solar time (LMST) for the lander site while the ninth (
Mars Pathfinder
''Mars Pathfinder'' (''MESUR Pathfinder'') is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight, wheeled robot ...
) used local true solar time (LTST).
Information as to whether China's
Zhurong
Zhurong (), also known as Chongli (), is an important personage in Chinese mythology and Chinese folk religion. According to the '' Huainanzi'' and the philosophical texts of Mozi and his followers, Zhurong is a god of fire and of the south.
Th ...
rover project has used a similar timekeeping system of recording the sol number and LMST (or offset) has not been disseminated.
''Viking'' Landers
The "local lander time" for the two ''Viking'' mission landers were offsets from LMST at the respective lander sites. In both cases, the initial clock midnight was set to match local true midnight immediately preceding touchdown.
''Pathfinder''
Mars ''Pathfinder'' used the local apparent solar time at its location of landing. Its time zone was AAT-02:13:01, where "AAT" is Airy Apparent Time, meaning apparent (true) solar time at Airy-0. The difference between the true and mean solar time (AMT and AAT) is the Martian
equation of time
In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in ...
.
Pathfinder kept track of the days with a sol count starting on Sol 1 (corresponding to MSD 43905), on which it landed at night at 02:56:55 (mission clock; 4:41 AMT).
''Spirit'' and ''Opportunity''
The two
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...
s did not use mission clocks matched to the LMST of their landing points. For mission planning purposes, they instead defined a time scale that would approximately match the clock to the apparent solar time about halfway through the nominal 90-sol primary mission. This was referred to in mission planning as "Hybrid Local Solar Time" (HLST) or as the "MER Continuous Time Algorithm". These time scales were uniform in the sense of mean solar time (i.e., they approximate the mean time of some longitude) and were not adjusted as the rovers traveled. (The rovers traveled distances that could make a few seconds difference to local solar time.) The HLST of ''Spirit'' is AMT+11:00:04 whereas the LMST at its landing site is AMT+11:41:55. The HLST of ''Opportunity'' is AMT-01:01:06 whereas the LMST at its landing site is AMT-00:22:06. Neither rover was likely to ever reach the longitude at which its mission time scale matches local mean time. However, for atmospheric measurements and other science purposes, Local True Solar Time is recorded.
''Spirit'' and ''Opportunity'' both started their sol counts with Sol 1 on the day of landing, corresponding to MSD 46216 and MSD 46236, respectively.
''Phoenix''
The ''
Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
'' lander project specified a mission clock that matched Local Mean Solar Time at the planned landing longitude of 126.65°W (233.35°E). This corresponds to a mission clock of AMT-08:26:36. The actual landing site was 0.900778° (19.8 km) east of that, corresponding to 3 minutes and 36 seconds later in local solar time. The date is kept using a mission clock sol count with the landing occurring on Sol 0, corresponding to MSD 47776 (mission time zone); the landing occurred around 16:35 LMST, which is MSD 47777 01:02 AMT.
''Curiosity''
The ''Curiosity'' rover project specified a mission clock that matched Local Mean Solar Time at its originally planned landing longitude of 137.42°E. This corresponds to a mission clock of AMT+09:09:40.8. The actual landing site was about 0.02° (1.3 km) east of that, a difference of about 5 seconds in solar time. The local mean solar time is also affected by the rover motion; at 4.6°S, this is about 1 second of time difference for every 246 meters of displacement along the east-west direction. The date is kept using a mission clock sol count with the landing occurring on Sol 0, corresponding to MSD 49269 (mission time zone); the landing occurred around 14:53 LMST (05:53 AMT).
''InSight''
The ''
InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
'' lander project specified a mission clock that matched Local Mean Solar Time at its planned landing site of 135.97°E. This corresponds to a mission clock of AMT+09:03:53. The actual landing site was at 135.623447°E, or 0.346553° (20.5 km) west of the reference longitude, so the lander mission clock is 1 minute and 23 seconds ahead of the actual mean local solar time at the lander location. The date is kept using a mission clock sol count with the landing occurring on Sol 0, corresponding to MSD 51511 (mission time zone); landing occurred around 14:23 LMST (05:14 AMT).
''Perseverance''
The ''Perseverance'' rover project specified a mission clock that matched Local Mean Solar Time at a planned landing longitude of 77.43°E. This corresponds to a mission clock of AMT+05:09:43. The actual landing site was about 0.02° (1.2 km) east of that, a difference of about 5 seconds in solar time. The local mean solar time is also affected by the rover motion; at 18.4°N, this is about 1 second of time difference for every 234 meters of displacement in the east-west direction. The date is kept using a mission clock sol count with the landing occurring on Sol 0, corresponding to MSD 52304 (mission time zone); landing occurred around 15:54 LMST (10:44 AMT).
Summary
Years
Definition of year and seasons
The length of time for Mars to complete one orbit around the Sun in respect to the stars, is its
sidereal year
A sidereal year (, ; ), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars.
Hence, for Earth, it is also the time taken for the Sun to return to the ...
, and is about 686.98 Earth solar days (≈ 1.88 Earth years), or 668.5991 sols. Because of the eccentricity of Mars' orbit, the seasons are not of equal length. Assuming that seasons run from equinox to solstice or vice versa, the season Ls 0 to Ls 90 (northern-hemisphere spring / southern-hemisphere autumn) is the longest season lasting 194 Martian sols, and Ls 180 to Ls 270 (northern hemisphere autumn / southern-hemisphere spring) is the shortest season, lasting only 142 Martian sols.
As on Earth, the sidereal year is not the quantity that is needed for calendar purposes. Similarly, the
tropical year
A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time fro ...
would likely be used because it gives the best match to the progression of the seasons. It is slightly shorter than the sidereal year due to the
precession
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In othe ...
of Mars' rotational axis. The precession cycle is 93,000 Martian years (175,000 Earth years), much longer than on Earth. Its length in tropical years can be computed by dividing the difference between the sidereal year and tropical year by the length of the tropical year.
Tropical year length depends on the starting point of measurement, due to the effects of
Kepler's second law
In astronomy, Kepler's laws of planetary motion, published by Johannes Kepler between 1609 and 1619, describe the orbits of planets around the Sun. The laws modified the heliocentric theory of Nicolaus Copernicus, replacing its circular orbits ...
of planetary motion and
precession
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In othe ...
. There are various possible years including the March (northward) equinox year, June (northern) solstice year, the September (southward) equinox year, the December (southern) solstice year, and the tropical year based on the
mean sun
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Two types of solar time are apparent solar time ( sundial t ...
. (See March equinox year.)
On Earth, the variation in the lengths of the tropical years is small, with the mean time from June solstice to June solstice being about a thousandth of a day shorter than that between two December solstices, but on Mars it is much larger because of the greater eccentricity of its orbit. The northward equinox year is 668.5907 sols, the northern solstice year is 668.5880 sols, the southward equinox year is 668.5940 sols, and the southern solstice year is 668.5958 sols (0.0078 sols more than the northern solstice year). (Since, like Earth, the northern and southern hemispheres of Mars have opposite seasons, equinoxes and solstices must be labelled by hemisphere to remove ambiguity.)
Seasons begin at 90 degree intervals of
solar longitude
Solar longitude, commonly abbreviated as Ls, is the ecliptic longitude of the sun, i.e. the position of the sun on the celestial sphere along the ecliptic. It is also an effective measure of the position of the earth (or any other sun-orbiting bod ...
(Ls) at
equinox
A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...
es and
solstice
A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many countr ...
s.
Year numbering
For purposes of enumerating Mars years and facilitating data comparisons, a system increasingly used in the scientific literature, particularly studies of Martian climate, enumerates years relative to the northern spring equinox (Ls 0) that occurred on April 11, 1955, labeling that date the start of Mars Year 1 (MY1). The system was first described in a paper focused on seasonal temperature variation by R. Todd Clancy of the
Space Science Institute
The Space Science Institute (SSI) in Boulder, Colorado, is a nonprofit, public-benefit corporation formed in 1992. Its purpose is to create and maintain an environment where scientific research and education programs can flourish in an in ...
. Although Clancy and co-authors described the choice as "arbitrary", the great dust storm of 1956 falls in MY1. This system has been extended by defining Mars Year 0 (MY0) as beginning May 24, 1953, and so allowing for negative year numbers.
Martian calendars
Long before mission control teams on Earth began scheduling work shifts according to the Martian sol while operating spacecraft on the surface of Mars, it was recognized that humans probably could adapt to this slightly longer diurnal period. This suggested that a calendar based on the sol and the Martian year might be a useful timekeeping system for astronomers in the short term and for explorers in the future. For most day-to-day activities on Earth, people do not use
Julian day
The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date).
...
s, as astronomers do, but the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...
, which despite its various complications is quite useful. It allows for easy determination of whether one date is an anniversary of another, whether a date is in winter or spring, and what is the number of years between two dates. This is much less practical with Julian days count. For similar reasons, if it is ever necessary to schedule and co-ordinate activities on a large scale across the surface of Mars it would be necessary to agree on a calendar.
American astronomer
Percival Lowell
Percival Lowell (; March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, and furthered theories of a ninth planet within the Solar System. ...
expressed the time of year on Mars in terms of Mars dates that were analogous to Gregorian dates, with 20 March, 21 June, 22 September, and 21 December marking the southward equinox, southern solstice, northward equinox, and northern solstice, respectively; Lowell's focus was on the southern hemisphere of Mars because it is the hemisphere that is more easily observed from Earth during favorable oppositions. Lowell's system was not a true calendar, since a Mars date could span nearly two entire sols; rather it was a convenient device for expressing the time of year in the southern hemisphere in lieu of heliocentric longitude, which would have been less comprehensible to a general readership.
Italian astronomer Mentore Maggini's 1939 book describes a calendar developed years earlier by American astronomers Andrew Ellicott Douglass and William H. Pickering, in which the first nine months contain 56 sols and the last three months contain 55 sols. Their calendar year begins with the northward equinox on 1 March, thus imitating the original
Roman calendar
The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the Roman dictator, dictator Julius Caesar and Roman emperor, emperor Augustus in the ...
. Other dates of astronomical significance are: northern solstice, 27 June; southward equinox, 36 September; southern solstice, 12 December; perihelion, 31 November; and aphelion, 31 May. Pickering's inclusion of Mars dates in a 1916 report of his observations may have been the first use of a Martian calendar in an astronomical publication. Maggini states: "These dates of the Martian calendar are frequently used by observatories...." Despite his claim, this system eventually fell into disuse, and in its place new systems were proposed periodically which likewise did not gain sufficient acceptance to take permanent hold.
In 1936, when the
calendar reform
Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.
Principles
The prime objective of a calendar is to unambigu ...
movement was at its height, American astronomer Robert G. Aitken published an article outlining a Martian calendar. In each quarter there are three months of 42 sols and a fourth month of 41 sols. The pattern of seven-day weeks repeats over a two-year cycle, i.e., the calendar year always begins on a Sunday in odd-numbered years, thus effecting a perpetual calendar for Mars.
Whereas previous proposals for a Martian calendar had not included an epoch, American astronomer I. M. Levitt developed a more complete system in 1954. In fact, Ralph Mentzer, an acquaintance of Levitt's who was a watchmaker for the Hamilton Watch Company, built several clocks designed by Levitt to keep time on both Earth and Mars. They could also be set to display the date on both planets according to Levitt's calendar and epoch (the
Julian day
The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date).
...
epoch of 4713 BCE).
Charles F. Capen included references to Mars dates in a 1966
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
technical report associated with the
Mariner 4
Mariner 4 (together with Mariner 3 known as Mariner-Mars 1964) was the Mariner program, fourth in a series of spacecraft intended for planetary exploration in a flyby mode. It was designed to conduct closeup scientific observations of Mars and ...
flyby of Mars. This system stretches the Gregorian calendar to fit the longer Martian year, much as Lowell had done in 1895, the difference being that 20 March, 21 June, 22 September, and 21 December marks the northward equinox, northern solstice, southward equinox, southern solstice, respectively. Similarly, Conway B. Leovy et al. also expressed time in terms of Mars dates in a 1973 paper describing results from the
Mariner 9
Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from LC-36B at Cape Canaveral Air ...
Mars orbiter.
British astronomer
Sir Patrick Moore
Sir Patrick Alfred Caldwell-Moore (; 4 March 1923 – 9 December 2012) was an English amateur astronomer who attained prominence in that field as a writer, researcher, radio commentator and television presenter.
Moore was president of the Brit ...
described a Martian calendar of his own design in 1977. His idea was to divide up a Martian year into 18 months. Months 6, 12 and 18, have 38 sols, while the rest of the months contain 37 sols.
American aerospace engineer and political scientist Thomas Gangale first published regarding the
Darian calendar
The Darian calendar is a proposed system of timekeeping designed to serve the needs of any possible future human settlers on the planet Mars. It was created by aerospace engineer, political scientist, and space jurist Thomas Gangale in 1985 and ...
in 1986, with additional details published in 1998 and 2006. It has 24 months to accommodate the longer Martian year while keeping the notion of a "month" that is reasonably similar to the length of an Earth month. On Mars, a "month" would have no relation to the orbital period of any moon of Mars, since Phobos and Deimos orbit in about 7 hours and 30 hours respectively. However, Earth and Moon would generally be visible to the naked eye when they were above the horizon at night, and the time it takes for the Moon to move from maximum separation in one direction to the other and back as seen from Mars is close to a
Lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Europ ...
.
Czech astronomer Josef Šurán offered a Martian calendar design in 1997, in which a common year has 672 Martian days distributed into 24 months of 28 days (or 4 weeks of 7 days each); in skip years an entire week at the end of the twelfth month is omitted.
Moore's 37-sol period
37 sols is the smallest integer number of sols after which the Mars Sol Date and the Julian date become offset by a full day. Alternatively, it can be viewed as the smallest integer number of sols needed for any Martian time zones to complete a full lap around Earth time zones. Specifically, 37 sols are equal to 38 Earth days plus 24 minutes and 44 seconds.
Remarkably, the 37-sol period also accidentally almost divides several time quantities of interest at the same time. In particular:
* One Martian year is approximately equal to 18 × (37 sols) + 2.59897 sols
* Two Earth-Mars synodic periods are approximately equal to 41 × (37 sols) + 1.176 sols
* One Earth decade is approximately equal to 96 × (37 sols) + 2.7018 sols
This makes the 37-sol period useful both for time synchronization between Earth and Mars timezones, and for Martian calendars, as a small number of leap sols can be straightforwardly added to eliminate calendar drift with respect to either the Martian year, Earth-Mars launch windows, or Earth calendars.
List of notable events in Martian history
Martian time in fiction
The first known reference to time on Mars appears in
Percy Greg
Percy Greg (7 January 1836 Bury – 24 December 1889, Chelsea), son of William Rathbone Greg, was an English writer.
Percy Greg, like his father, wrote about politics, but his views were violently reactionary: his ''History of the United States t ...
's novel ''
Across the Zodiac
''Across the Zodiac: The Story of a Wrecked Record'' (1880) is a science fiction novel by Percy Greg, who has been credited as an originator of the sword and planet subgenre of science fiction.
Plot
The book details the creation and use of a ...
'' (1880). The primary, secondary, tertiary, and quaternary divisions of the sol are based on the number 12. Sols are numbered 0 through the end of the year, with no additional structure to the calendar. The epoch is "the union of all races and nations in a single State, a union which was formally established 13,218 years ago".
20th century
Edgar Rice Burroughs
Edgar Rice Burroughs (September 1, 1875 – March 19, 1950) was an American author, best known for his prolific output in the adventure, science fiction, and fantasy genres. Best-known for creating the characters Tarzan and John Carter, he ...
described, in ''The Gods of Mars'' (1913), the divisions of the sol into zodes, xats, and tals. Although possibly the first to make the mistake of describing the Martian year as lasting 687 Martian days, he was far from the last.
In the
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 accu ...
novel '' Red Planet'' (1949), humans living on Mars use a 24-month calendar, alternating between familiar Earth months and newly created months such as Ceres and Zeus. For example, Ceres comes after March and before April, while Zeus comes after October and before November.
The Arthur C. Clarke novel ''
The Sands of Mars
''The Sands of Mars'' is a science fiction novel by English writer Arthur C. Clarke. While he was already popular as a short story writer and as a magazine contributor, ''The Sands of Mars'' was also a prelude to Clarke's becoming one of the ...
'' (1951) mentions in passing that "Monday followed Sunday in the usual way" and "the months also had the same names, but were fifty to sixty days in length".
In
H. Beam Piper
Henry Beam Piper (March 23, 1904 – ) was an American science fiction writer. He wrote many short stories and several novels. He is best known for his extensive Terro-Human Future History series of stories and a shorter series of "Paratime" alt ...
's short story " Omnilingual" (1957), the Martian calendar and the periodic table are the keys to archaeologists' deciphering of the records left by the long dead Martian civilization.
Kurt Vonnegut
Kurt Vonnegut Jr. (November 11, 1922 – April 11, 2007) was an American writer known for his satirical and darkly humorous novels. In a career spanning over 50 years, he published fourteen novels, three short-story collections, five plays, and ...
's novel ''
The Sirens of Titan
''The Sirens of Titan'' is a comic science fiction novel by Kurt Vonnegut Jr., first published in 1959. His second novel, it involves issues of free will, omniscience, and the overall purpose of human history. Much of the story revolves around a ...
'' (1959) describes a Martian calendar divided into twenty-one months: "twelve with thirty days, and nine with thirty-one", for a total of only 639 sols.
D. G. Compton
David Guy Compton (born August 19, 1930) is a British author who writes science fiction under the name D. G. Compton. He used the name Guy Compton for his earlier crime novels and the pseudonym Frances Lynch for his Gothic novels. He has also writ ...
states in his novel ''Farewell, Earth's Bliss'' (1966), during the prison ship's journey to Mars: "Nobody on board had any real idea how the people in the settlement would have organised their six-hundred-and-eighty-seven-day year."
In Ian McDonald's ''
Desolation Road
''Desolation Road'' is a 1988 science fiction novel written by Ian McDonald. It was McDonald's first published novel. The plot takes place on a far future Mars in a town that develops around an oasis in the terraformed Martian desert. McDonald ...
'' (1988), set on a terraformed Mars (referred to by the book's characters as "Ares"), characters follow an implied 24-month calendar whose months are
portmanteau
A portmanteau word, or portmanteau (, ) is a blend of wordsPhilip K. Dick's novel ''
Martian Time-Slip
''Martian Time-Slip'' is a 1964 science fiction novel by American writer Philip K. Dick. The novel uses the common science fiction concept of a human colony on Mars. However, it also includes the themes of mental illness, the physics of time an ...
'' and
Kim Stanley Robinson
Kim Stanley Robinson (born March 23, 1952) is an American writer of science fiction. He has published twenty-two novels and numerous short stories and is best known for his ''Mars'' trilogy. His work has been translated into 24 languages. Many ...
's ''
Mars Trilogy
The ''Mars'' trilogy is a series of science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the personal and detailed viewpoints of a wide variety of characters spanning almost tw ...
'' (1992–1996), clocks retain Earth-standard seconds, minutes, and hours, but freeze at midnight for 39.5 minutes. As the fictional
colonization of Mars
Colonization or settlement of Mars is the theoretical human migration and long-term human establishment of Mars. The prospect has garnered interest from public space agencies and private corporations and has been extensively explored in scien ...
progresses, this "timeslip" becomes a sort of
witching hour
In folklore, the witching hour or devil's hour is a time of night that is associated with supernatural events, whereby witches, demons and ghosts are thought to appear and be at their most powerful. Definitions vary, and include the hour imm ...
, a time when inhibitions can be shed, and the emerging identity of Mars as a separate entity from Earth is celebrated. (It is not said explicitly whether this occurs simultaneously all over Mars, or at local midnight in each longitude.) Also in the ''
Mars Trilogy
The ''Mars'' trilogy is a series of science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the personal and detailed viewpoints of a wide variety of characters spanning almost tw ...
'', the calendar year is divided into twenty-four months. The names of the months are the same as the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...
, except for a "1" or "2" in front to indicate the first or second occurrence of that month (for example, 1 January, 2 January, 1 February, 2 February).
21st century
In the
manga
Manga (Japanese: 漫画 ) are comics or graphic novels originating from Japan. Most manga conform to a style developed in Japan in the late 19th century, and the form has a long prehistory in earlier Japanese art. The term ''manga'' is u ...
and
anime
is Traditional animation, hand-drawn and computer animation, computer-generated animation originating from Japan. Outside of Japan and in English, ''anime'' refers specifically to animation produced in Japan. However, in Japan and in Japane ...
series ''
Aria
In music, an aria (Italian: ; plural: ''arie'' , or ''arias'' in common usage, diminutive form arietta , plural ariette, or in English simply air) is a self-contained piece for one voice, with or without instrumental or orchestral accompanime ...
'' (2001–2002), by
Kozue Amano
is a Japanese manga artist. She is widely known as the creator of ''Aria (manga), Aria'', which proved to be a best-selling hit, and was adapted into an anime television series consisting of 3 seasons and 2 Original video animation, OVAs.
As o ...
, set on a
terraformed
Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make ...
Mars, the calendar year is also divided into twenty-four months. Following the modern
Japanese calendar
Japanese calendar types have included a range of official and unofficial systems. At present, Japan uses the Gregorian calendar together with year designations stating the year of the reign of the current Emperor. The written form starts with t ...
, the months are not named but numbered sequentially, running from 1st Month to 24th Month.
The Darian calendar is mentioned in a couple of 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
''The Quantum Thief'' is the debut science fiction novel by Finnish writer Hannu Rajaniemi and the first novel in a trilogy featuring the character of Jean le Flambeur; the sequels are '' The Fractal Prince'' (2012) and '' The Causal Angel'' (201 ...
'' by
Hannu Rajaniemi
Hannu Rajaniemi (born 9 March 1978) is a Finnish American author of science fiction and fantasy, who writes in both English and Finnish. He lives in Oakland, California, and was a founding director of a commercial research organisation ThinkTan ...
, Tor Books; Reprint edition (May 10, 2011)
In
Andy Weir
Andrew Taylor Weir (born June 16, 1972) is an American novelist and former computer programmer. His 2011 novel '' The Martian'' was adapted into the 2015 film of the same name directed by Ridley Scott. He received the John W. Campbell Award fo ...
's novel '' The Martian'' (2011) and its 2015 feature film adaptation, sols are counted and referenced frequently with onscreen title cards, in order to emphasize the amount of time the main character spends on Mars. "Ares 3 launched on July 7, 2035. They landed on Mars (Sol 1) on November 7, 2035. The story begins on Sol 6, which is November 12, 2035." – Andy Weir
Julian date
The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date).
...
referred to
Terrestrial Time
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth.
For example, the Astronomical Almanac uses T ...
(TT), asThis is a trivial simplification of the formula (JDTT − 2451549.5) / 1.0274912517 + 44796.0 − 0.0009626 given i Mars24 Algorithm and Worked Examples
:MSD = (JDTT − 2405522.0028779) / 1.0274912517
Terrestrial time, however, is not as easily available as
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used ...
(UTC). TT can be computed from UTC by first adding the difference TAI−UTC, which is a positive integer number of seconds occasionally updated by the introduction of
leap second
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observe ...
s (see current number of leap seconds), then adding the constant difference TT−TAI = 32.184 s. This leads to the following formula giving MSD from the UTC-referred Julian date:
:MSD = (JDUTC + (TAI−UTC)/86400 − 2405522.0025054) / 1.0274912517
where the difference TAI−UTC is in seconds. JDUTC can in turn be computed from any epoch-based time stamp, by adding the Julian date of the epoch to the time stamp in days. For example, if is a Unix timestamp in seconds, then
:JDUTC = / 86400 + 2440587.5
It follows, by a simple substitution:
:MSD = ( + (TAI−UTC)) / 88775.244147 + 34127.2954262
MTC is the fractional part of MSD, in hours, minutes and seconds:
:MTC = (MSD
mod
Mod, MOD or mods may refer to:
Places
* Modesto City–County Airport, Stanislaus County, California, US
Arts, entertainment, and media Music
* Mods (band), a Norwegian rock band
* M.O.D. (Method of Destruction), a band from New York City, US ...
1) × 24 h
For example, at the time this page was last generated ():
* JDTT =
* MSD =
* MTC =
See also
*
Astronomy on Mars
In many cases astronomical phenomena viewed from the planet Mars are the same or similar to those seen from Earth but sometimes (as with the view of Earth as an evening/morning star) they can be quite different. For example, because the atmosp ...
*
Universal Time
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with ...
*
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used ...
Curiosity Rover
''Curiosity'' is a car-sized Mars rover designed to explore the Gale crater on Mars as part of NASA's Mars Science Laboratory (MSL) mission. ''Curiosity'' was launched from Cape Canaveral (CCAFS) on November 26, 2011, at 15:02:00 UTC and lan ...
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...