Timekeeping On Mars - Calendar Dates

Calendar Dates

Mars scientists typically keep track of the Martian year by use of the heliocentric longitude (or "seasonal longitude"), typically abbreviated L_s, the position of Mars in its orbit around the Sun. L_s is defined as 0 degrees at the Martian northward equinox, and hence is 90 degrees at the Martian northern solstice, 180 at the Martian southward equinox, and 270 degrees at the Martian southern solstice.

For most day-to-day activities on Earth, people don't use Julian days, but the Gregorian calendar, 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. One proposed calendar is the Darian calendar. 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. Neither the Darian calendar nor any other Martian calendar is currently in use.