How does timekeeping work on Mars?
Mars has an axial tilt and a rotation period similar to those of Earth. Thus it experiences seasons of spring, summer, autumn and winter much like Earth, and its day is about the same length. Its year is almost twice as long as Earth's, and its orbital eccentricity is considerably larger, which means among other things that the lengths of various Martian seasons differ considerably, and sundial time can diverge from clock time more than on Earth.
Time of the day
The average length of a Martian sidereal day is 24h 37m 22.663s (88,642.66300 seconds based on SI units), and the length of its solar day (often called a sol) is 24h 39m 35.244147s (88,775.244147 seconds). The corresponding values for Earth are 23h 56m 4.0916s and 24h 00m 00.002s, respectively. This yields a conversion factor of 1.02749125170 days/sol. Thus Mars' solar day is only about 2.7% longer than Earth's.
Sols
The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars. A mean Martian solar day, or "sol", is 24 hours, 39 minutes, and 35.244 seconds.
When a spacecraft lander begins operations on Mars, the passing Martian days (sols) are tracked using a simple numerical count. The two Viking missions, Mars Phoenix and the Mars Science Laboratory rover Curiosity count the sol on which each lander touched down as "Sol 0"; Mars Pathfinder and the two Mars Exploration Rovers instead defined touchdown as "Sol 1".
Martian year
The length of time for Mars to complete one orbit around the Sun is its sidereal year, and is about 686.98 Earth solar days, or 668.5991 sols. Because of the eccentricity of Mars' orbit, the seasons are not of equal length.
