Martian Seasons and Solar Longitude

Martian Solar Longitude Ls

The solar longitude Ls is the Mars-Sun angle, measured from the Northern Hemisphere spring equinox where Ls=0.
Ls=90 thus corresponds to summer solstice, just as Ls=180 marks the autumn equinox and Ls=270 the winter solstice (all relative to the northern hemisphere).
Martian Solar longitude

Martian days (sols) and months

A martian year is 668.6 sols (martian solar days) long and a sol is 88775.245 seconds long.
Martian months are defined as spanning 30 degrees in solar longitude. Due to the eccentricity of Mars' orbit, martian months are thus from 46 to 67 sols long, as shown in the table below.

Month
number
Ls range
(degrees)
Sol range
 
duration
(in sols)
specificities
 
1 0 30 0.0 61.2 61.2 Northern Hemisphere Spring Equinox at Ls=0
2 30 60 61.2 126.6 65.4  
3 60 90 126.6 193.3 66.7 Aphelion (largest Sun-Mars distance) at Ls=71
4 90 120 193.3 257.8 64.5 Northern Hemisphere Summer Solstice at Ls=90
5 120 150 257.8 317.5 59.7  
6 150 180 317.5 371.9 54.4  
7 180 210 371.9 421.6 49.7 Northern Hemisphere Autumn Equinox at Ls=180
Dust Storm Season begins
8 210 240 421.6 468.5 46.9 Dust Storm Season
9 240 270 468.5 514.6 46.1 Perihelion (smallest sun-Mars distance) at Ls=251
Dust Storm Season
10 270 300 514.6 562.0 47.4 Northern hemisphere Winter Solstice at Ls=270
Dust Storm Season
11 300 330 562.0 612.9 50.9 Dust Storm Season
12 330 360 612.9 668.6 55.7 Dust Storm Season ends

Martian time keeping

Martian hours are (just as their earth counterparts) defined as lasting 1/24th of a sol.
In order to avoid confusions, we do not use (or define) martian minutes or seconds: any (martian) time of day is always given as martian hours and decimal fraction thereof.

Local time

Time is given as Local True Solar Time at longitude 0, LTST0 (denoted UMST in the Mars Climate Database).

For the sake of simplicity, we do not use or define time zones. Local True Solar Time LTST at east longitude lon (in degrees) can easily computed as:
LTST = LTST0 + lon/15

Local True Solar Time is related to the position of the sun in the sky: Noon occurs when the sun is highest in the sky, at local true solar time LTST=12.0 martian hours (in other words, Local True Solar Time is the value that would be read on a sundial).

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