Cycles and units

Submitted by mossy2100 on Tue, 04/25/2017 - 00:08

Before getting into how the calendar works, it is useful to review the Martian astronomical cycles on which it is based, and the terms and units used in the explanation of the calendar:

  • A Martian day is called a sol, which is an abbreviation of “solar day”. A sol has an average duration of 88775.24409 seconds, which is 1.02749 days, or 24 hours, 39 minutes, and 35.24409 seconds. Thus, a sol is only about 40 minutes, or 2.75%, longer than a Terran day. The word “sol” was introduced by NASA during the Viking missions, and has been used to refer to a Martian solar day ever since. The fact that a sol is almost the same length as a day is tremendously convenient when designing a calendar, because it permits the creation of one very similar to those we’re already familiar with, which use the day – the dominant cycle of human behaviour and society – as their fundamental unit.
  • Corresponding terms were developed by the Curiosity mission team, including tosol (today), yestersol (yesterday), nextersol (tomorrow), and soliday (holiday).
  • Using SI prefixes, the terms decisol (1 dsol = 0.1 sol), centisol (1 csol = 0.01 sol), millisol (1 msol = 0.001 sol), microsol (1 µsol = 10‑6 sol), and nanosol (1 nsol = 10‑9 sol) are derived. Thus, there are 10 decisols in a sol, 100 millisols in a decisol, and 1000 microsols in a millisol.
  • The term mir is used for “Martian year”. “Mir” is a Russian word that means “world”, “peace”, and “community”, and was the name of the legendary Russian space station. It means “community” in the sense of a community combining their efforts for a common task, such as building a church or clearing a field. The word “mir” not only sounds like a perfect contraction of “Martian year”, but also invokes the spirit of a group working together with the common cause of developing Mars into a peaceful world community. A mir has about 668.5907 sols, on average, which is equal to about 687 days or 1.88 years.
  • Also using SI prefixes, the terms decamir (1 damir = 10 mir), hectomir (1 hmir = 100 mir), kilomir (1 kmir = 1000 mir), megamir (1 Mmir = 106 mir), and gigamir (1 Gmir = 109 mir) are derived, for Martian decade, century, millennium, mega-annum, and giga-annum respectively.
  • The units week and month as used in the calendar do not refer to precise periods of time, but rather to periods similar in duration and purpose to weeks and months on Earth.