Because Mars has a different orbit than Earth, the year (one orbit around the Sun) is almost twice as long. Also, Mars axis is tilted (25 degrees) much like Earth (23.5 degrees) so it has four seasons.
There is a 19% difference in the orbit between Mars perihelion (closest approach to the Sun) and its aphelion (farthest point from the Sun.) The aphelion occurs near the time of the Northern hemisphere Summer Solstice which means it is closest to the Sun (and is at its top orbital speed) during Summer in the Southern hemisphere (like Earth.)
The result of this orbit is that the Southern hemisphere has short, but warm summers, followed by long, cold winters.
Because the physical environment on Mars is important to human occupation, the designation of a calendar specific to the planet is advantageous for this mission. For that reason we have created a Mars calendar. This calendar begins at Winter Solstice for the Southern hemisphere beginning 3 January 2016.
Mars ‘months’ are establish by taking the number of days in each ‘season’ and dividing them into three approximately equal months. Note that each Mars day is 24 hours, 37 minutes long, so each Earth day is .97 as long as a Mars day.
The Mars ‘year’ is divided into two sections, the Southern New Year and the Northern New Year. Each section consists of six Mars ‘months’ and those six are divided into two three month ‘seasons’ (Sur Winter, Sur Spring, Nor Winter, Nor Spring.) Summer and Fall seasons for each hemisphere occur during the opposite hemisphere’s Winter and Fall.
Mars Southern New Year (Northern Summer Solstice) begins on Earth 3 JAN 2016.
Sur Winter (Length – 183 Earth Days/178 Mars Days) – Begins 3 Jan 2016 ED
Sur Spring – (Length – 147 Earth Days/143 Mars Days) – Begins 4 JUL 2016 ED
Mars Northern New Year (Southern Summer Solstice) begins on Earth 28 Nov 2016.
Nor Winter (Length – 158 Earth Days/154 Mars Days) – Begins 28 Nov 2016 ED
Nor Spring (Length – 199 Earth Days/193 Mars Days) – Begins 5 May 2017 ED
Next Seasons (Earth Day)
- Sur Winter – 20 NOV 2017
- Sur Spring – 22 MAY 2018
- Nor Winter – 16 OCT 2018
- Nor Spring – 23 MAR 2019
- Sur Winter – 8 OCT 2019
- Sur Spring – 8 APR 2020
- Nor Winter – 2 SEP 2020
- Nor Spring – 7 FEB 2021