• Mars Date/Time:  Year 1, Sur One, Sol 25 (1.1.25)  3:38 PM NST
• Earth Date/Time:  28 January 2016  2:00 PM PST

Creating the Martian calendar required understand why Earth’s calendar is divided into units. In some cases there is a clear astronomical reason (one planet rotation equals a day,) but other units, such as weeks, have no celestial cycle to establish the unit.

However, the month and year on Earth can be traced to certain astronomical patterns.

MONTH and YEAR
Earth months are loosely based on the orbit of the Moon. The Moon orbits Earth more than twelve times per year, but there is a clear link between the phases of the Moon, and the length of a month.

Mars has two Moons, but they’re orbits are not useful in establishing a time unit similar to Earth’s month standard; however, because Mars is tilted on its axis similar to Earth, it does experience seasons. Those season’s can be measured by the two equinoxes and two solstices.

However, because the orbit of Mars takes almost twice as many days (Earth days) than Earth, the seasons are almost twice as long and they have more variance (length) than Earth’s seasons.

To establish a Mars month, ESEP divided the Mars year (one orbit around the Sun) into four seasons. Each of those seasons are divided into three, roughly equal months. The full Mars calendar can be seen here.

ESEP began the calendar on the Winter solstice for the Southern Hemisphere, which occurred on 3 January 2016 (Earth Date.) The first six months are measured by the Winter and Spring in the Southern Hemisphere (called Sur) and the second six months are measured by the Winter and Spring of the Northern Hemisphere (called Nor.)