This document is part of the Martian Time Boneyard. It was originally located at http://www.marsengineering.com/Calendar/Terminology.asp.
Author: Shaun Moss

Terminology

sol = Martian solar day. This term was first used by the NASA JPL Viking mission team in 1976 and is now widely accepted within the Mars community. It refers to the average length of the Martian solar day, 88775.24409 seconds (24 hours, 39 minutes, and 35.24409 seconds). One sol is thus only fractionally longer than an Earth day. This is one of the most compelling reasons for colonization of Mars, as humans and other Earthly organisms with a biological cycle of 24 hours should have little difficulty adapting to the Martian day/night cycle.

Other new terms can easily be derived from 'sol', for example: 'tosol', 'yestersol', 'holisol', and 'birthsol'.

mir = Martian year. This is a new term introduced in the Utopian Calendar, quite similar to the term 'mear' used by Robert L. Foward in his 1991 novel 'Martian Rainbow'. One mir is approximately equal to 1.88 years. As we may refer to a tropical year or calendar year, so may we refer to a tropical mir or calendar mir. This particular word was selected for several reasons:

• in remembrance of the famous space station
• it sounds like a contraction of 'Martian year'
• it means 'peace', 'commune' and 'world'
• it's easy to remember

It may be useful to have Martian equivalents for 'decade', 'century', and 'millennium'. These are easily defined using SI prefixes:

10 mirs	= 1 dekamir	= 1.88 decades
100 mirs	= 1 hectomir	= 1.88 centuries
1000 mirs	= 1 kilomir	= 1.88 millennia

The terms 'month' and 'week' are used in the context you would expect. It doesn't seem necessary to define new terms meaning 'Martian month' or 'Martian week'.

The word 'month' literally means 'moon', and originally meant the period of time between two new moons - a duration now referred to as a 'Lunar month'. Because of the complex motion of the moon, Lunar months vary slightly in duration, although the average length of a Lunar month is known precisely: 29.5305888531 days. On Earth, the term 'month' is commonly understood to mean a 'calendar' month, or 'a fraction of the calendar year approximately equal in duration to a Lunar month', and may refer to a period of 28, 29, 30, or 31 days.

The term 'month' is thus not a reference to an exact time unit, nor is it used in precise calculations, but primarily in determination of calendar dates. There is therefore little reason for invention of a new term meaning 'Martian month', as long as it's defined similarly to an Earth month, namely, 'a fraction of the calendar mir approximately equal in duration to a Lunar month'. A Lunar month is equal to 28.74 sols, therefore Martian months should preferably be approximately of this duration.

The term 'week' is also not employed as a precise time unit. There's no known astronomical basis for the week - it evolved as a standard work-rest cycle (or the period between market days) and historically has ranged in length between 4 and 10 days. Because the week is not used as a exact time unit, but rather as a definition of the work-rest cycle, there also seems little reason to invent a new term for 'Martian week'.