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

Formats

The format for Martian dates is very important, because, as with Gregorian dates, there exists the possibility of confusion between different date fields. Fortunately, an international standard has already been established for the format of Gregorian dates, namely the ISO-8601 date format, that can easily be adopted for Utopian dates and times.

International Standard Date and Time Notation

In brief, the ISO-8601 standard specifies:

• Year, month, day, seperated by hyphens, for example: 2000-06-18
• The century is shown, i.e. the year is not abbreviated to 2 digits.
• Months and days are shown as two digits, with a 0 prepended if necessary.

There are several advantages of this standard. It favours neither the European convention of day-month-year, nor the American convention of month-day-year, thus, it's a diplomatic choice. Also, the most significant number (the year) is on the left and the least significant (the day) is on the right, in accordance with normal usage of numbers.

Mars Date and Time Notation

Paralleling this standard as closely as possible, a format for writing Mars dates and times can be defined as follows:

MIR-MM-SSTmil.mTZD

for example: 208-19-28T260.00+500

where:
MIR is the current mir shown with 3 or more digits, e.g. 000, 208, 1200
MM is the month shown as two digits, e.g. 01, 24
SS is the sol shown as two digits, e.g. 01, 28
T indicates the beginning of the time part
mil is the current mil shown as 3 digits, e.g. 000, 999
m one or more digits representing fractions of a mil
TZD is the Time Zone Designator, e.g. Z, +100, +900. "Z" indicates zero meridian time, also known as Mars Universal Time (MUT).

A date by itself can simply be written as MIR-MM-SS, e.g.
208-19-28

If compactness is more important than readability, then the hyphens can be omitted, e.g.
2081928

A time of sol written by itself can just show the mils, e.g.
500

If more precision is required, then fractions of a mil can be shown using decimal notation. Two decimal places indicates beats, e.g.
500.00

If it isn't clear that a single number indicates a time, the 'T' can be prepended, e.g.
T500.00

At least 3 digits for mirs

The Y2K problem highlighted the problems associated with abbreviating the year to two digits. That's why it's a good idea to write mirs using at least 3 digits, even if the mir is less than 100, for example: 013. This notation, first used by Michael Allison in the Mars Proleptic Calendar, clarifies which part of the date field denotes the mir.

Months can be shown using digits or letters

Although this is not part of ISO-8601, it is not unusual to write the month using letters, either fully or as an abbreviation (as has been done in the clock on this page). This indicates more clearly which part of the date field is the month, further minimizing confusion. As all constellations have a 3-letter abbreviation, we may conveniently use these in wirtten dates, e.g.
208-Gem-19