What time is it on Mars?

Mars turns once relative to the Sun every 24 hours, 39 minutes and 35.244 seconds. Mission controllers call that a sol to keep it apart from an Earth day, and the vocabulary followed: tomorrow on Mars is tosol, yesterday is yestersol. Engineers on early rover missions lived on Mars time, shifting their working day about 40 minutes later every day until "morning" meetings landed at 3 a.m.

The planet has its own Greenwich: a small crater called Airy-0, named after the Astronomer Royal who set up the Greenwich meridian. Mean solar time there is Coordinated Mars Time — the clock at the top of this page — and the running count of sols since 29 December 1873 is the Mars Sol Date, Mars's equivalent of the Julian Date.

Each rover counts sols from its landing day (sol 0) and runs on the local time of its crater. Two clocks matter: mean solar time (LMST), which ticks evenly, and true solar time (LTST), which follows the real Sun. Because Mars's orbit is lopsided — 9.3% eccentric against Earth's 1.7% — the two can disagree by about 50 minutes, compared with 16 minutes on Earth.

Scientists number Mars years from the northern spring equinox of 11 April 1955, which became the start of Mars Year 1 — a convention set in 2000 so that dust-storm records from different decades could be compared. A Mars year lasts 668.6 sols (686.98 Earth days). Position within the year is given by solar longitude, Ls: 0° at the northern spring equinox, 90° at the summer solstice and so on.

Mars Year 39 began on 30 September 2026. Because the orbit is so elliptical, the seasons are badly uneven: northern spring is the longest at about 194 sols, northern autumn the shortest at about 142. Southern summer, near perihelion (Ls ≈ 251°), is short and hot — and it is dust-storm season, when global storms can blanket the planet.

Earth laps Mars every 780 days on average. When Earth passes between Mars and the Sun — opposition — Mars is at its closest and brightest, up all night, and launch windows open a few months before. When Mars is on the far side of the Sun — solar conjunction — radio signals pass too close to the Sun, and mission teams stop sending commands for about two weeks.

The best known is the Darian calendar, devised by aerospace engineer Thomas Gangale in 1985: 24 months of 27 or 28 sols, giving 668 or 669 sols a year, with leap sols on a rule much like the Gregorian one. Its month names alternate between the Latin and Sanskrit names of the zodiac constellations. No space agency uses it — missions just count sols and quote Ls — but it is a neat thought experiment in how much of our calendar is habit rather than astronomy.