I'm writing a story about Mars and I'm really confused as to how one should use the word 'Sol when talking about the passage of time there. For example, Would one say to a colleague: "Today is Sol 345, Jack"


1 Answer 1


From the Wikipedia page on Martian timekeeping:

The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars.[7] A mean Martian solar day, or "sol", is 24 hours, 39 minutes, and 35.244 seconds.[6]

“Sol” is often used as a direct replacement for “Day” when concerning Mars. Mission duration for Mars missions is measured in Sols, so saying “Today is Sol xyz” would be normal, but I’m not sure if anyone would say “what a wonderful Sol tomorrow is going to be”.

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    $\begingroup$ I could imagine some pedantic conversation like: Team leader: "What a wonderful day it is!". Science Advisor: "Don't you mean 'what a wonderful SOL' ?" $\endgroup$ Commented Jan 26, 2015 at 12:56
  • $\begingroup$ “what a wonderful Sol tomorrow is going to be”. Funeee:) $\endgroup$
    – user67244
    Commented Jan 26, 2015 at 13:23
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    $\begingroup$ Sometimes we say "yestersol" and "solmorrow". $\endgroup$
    – Mark Adler
    Commented Jan 26, 2015 at 18:20
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    $\begingroup$ But is Sol global or local on Mars? Does every lander has its own midnight definition? Does it change as a rover moves? On Earth we have a definition of day for each time zone. When the Sun is on the opposite side of Earth, a new day begins. When does a global Sol begin? Are their timezones on Mars? How many, 24.6, or don't you use 12 h watches to keep track of mission time there? @MarkAdler $\endgroup$
    – LocalFluff
    Commented Oct 18, 2015 at 11:41
  • $\begingroup$ Local. Each lander has its own "time zone" with noon defined by the local mean solar time at the location of the landing. It does not change as the rover moves. (The variations in the true local noon due to the eccentricity of Mars' orbit is much greater than the change due to the trek of the rover.) There are 24 Mars hours in a Mars solar day, which are used for rover activity planning. There are no global time zones in use (though I'm sure someone has defined some for fun). $\endgroup$
    – Mark Adler
    Commented Oct 18, 2015 at 15:35

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