Timekeeping on Mars
[5] When accounting solar days on Earth, astronomers often use Julian dates—a simple sequential count of days—for timekeeping purposes.
Thus, the MSD is a running count of sols since 29 December 1873 (coincidentally the birth date of astronomer Carl Otto Lampland).
[6][7] 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.
Its temperature rises and falls rapidly at sunrise and sunset because Mars does not have Earth's thick atmosphere and oceans that soften such fluctuations.
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 in Terra Meridiani.
[11] 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.
[6] The abbreviation "MTC" was used in some versions of the related Mars24 Sunclock[14] coded by the NASA Goddard Institute for Space Studies.
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.
[15][16] When a NASA spacecraft lander begins operations on Mars, the passing Martian days (sols) are tracked using a simple numerical count.
[6][3] Information as to whether China's Zhurong rover project has used a similar timekeeping system of recording the sol number and LMST (or offset) has not been disseminated.
The Phoenix lander project specified a mission clock that matched Local Mean Solar Time at the planned landing longitude of 126.65°W (233.35°E).
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 Curiosity rover project specified a mission clock that matched Local Mean Solar Time at its originally planned landing longitude of 137.42°E.
The InSight lander project specified a mission clock that matched Local Mean Solar Time at its planned landing site of 135.97°E.
The Perseverance rover project specified a mission clock that matched Local Mean Solar Time at a planned landing longitude of 77.43°E.
Tropical year length depends on the starting point of measurement, due to the effects of Kepler's second law of planetary motion and precession.
The system was first described in a paper focused on seasonal temperature variation by R. Todd Clancy of the Space Science Institute.
[10] 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 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 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.
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.
[27] Whereas previous proposals for a Martian calendar had not included an epoch, American astronomer I. M. Levitt developed a more complete system in 1954.
[38] Edgar Rice Burroughs described, in The Gods of Mars (1913), the divisions of the sol into zodes, xats, and tals.
[41] The Arthur C. Clarke novel The Sands of Mars (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".
[43] Kurt Vonnegut's novel The Sirens of Titan (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.
[44] D. G. Compton 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.
[citation needed] In the manga and anime series Aria (2001–2002), by Kozue Amano, set on a terraformed Mars, the calendar year is also divided into twenty-four months.
[46] The Darian calendar is mentioned in a couple of works of fiction set on Mars: In Andy Weir'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.
