F - Comparative Calendar Reference

Selected Martian Calendar Architectures

F.1 Purpose and scope

More than seventy published approaches to Martian timekeeping had already been identified by Gangale and Dudley-Rowley by 2005. A complete historical catalogue would therefore be considerably larger than this appendix and would add little to the purpose of this book.

The aim here is narrower.

This appendix provides a compact reference to the principal calendar architectures discussed in the main text: Levitt, Darian, Zubrin, Šurán, Hargitai, Exodus and Marian. They were selected because together they expose most of the design choices that matter to Marian: twelve versus twenty-four primary annual periods, equal elapsed time versus stronger orbital representation, fixed recurrence versus uninterrupted weekly succession, distributed versus concentrated irregularity, and familiar versus explicitly Martian interfaces.

The dates given below refer to the principal publications discussed in this book rather than necessarily to the first moment at which each idea was conceived.

This is not a ranking.

The useful question is not which calendar contains the fewest unusual features. It is which properties each architecture chooses to preserve, and where it places the unavoidable cost.

F.2 Structural reference

Levitt's 1954 proposal explicitly used the twelve-month 56–56–55 structure and shortened the terminal week of the 55-sol months. Gangale's 1986 Martian Standard Time became the foundation of the later Darian system, whose roughly 28-sol primary months make a different choice about the scale worth preserving.

Zubrin's 1996 design deliberately divides Mars's annual progression into twelve equal angular sectors rather than twelve equal elapsed periods.Šurán's 1997 work is broader than a single layout: it explicitly compares perpetual calendars using leap or skip days and leap or skip weeks.

Hargitai's climate-data system uses eleven 56-sol months and a 52/53-sol final month, with the year beginning around Ls = 270°. Its published purpose was the presentation and comparison of Martian climatic data rather than the construction of a general civil constitution for Mars. Exodus, published by Silin in 2025, similarly uses eleven 56-sol months but retains terrestrial month names and places the remaining adjustment in December, which varies from 52 to 54 sols.

F.3 The functional comparison

The structural details become easier to understand when each calendar is viewed through the principal property it protects.

That is substantially the same comparison reached in Chapter 20: the designs become clearer when examined by what they are trying hardest to preserve, not by counting departures from the Gregorian calendar.

F.4 Levitt and Darian: the scale choice

Levitt and Darian expose perhaps the clearest single choice in Martian calendar design.

Levitt preserves twelve annual divisions. Its months are therefore approximately twice the duration of terrestrial months, but their position within the year remains immediately legible. The repeating 56–56–55 structure also produces four equal 167-sol common-year quarters.

Darian protects a different property. Its primary months normally contain 27 or 28 sols, preserving something much closer to the human-scale duration associated with a terrestrial month. The Martian year consequently requires twenty-four of them.

Neither result follows more correctly from the astronomy.

They answer different questions:

Should the month primarily preserve its fraction of the year, or its familiar human duration?

Marian's response is to preserve both scales and give them different names and functions. The Levitt-like scale becomes the month; the Darian-like scale becomes the minth. That relationship is central to Marian's Functional Separation principle.

F.5 Zubrin and Hargitai: what should a month represent?

Zubrin and Hargitai expose a different conflict.

Zubrin gives stronger weight to orbital position. His twelve months represent equal angular progress around the Sun. Because Mars moves at different speeds through its eccentric orbit, those equal angular sectors require unequal amounts of elapsed time.

Hargitai moves towards the opposite end of that axis. For climate-data presentation, repeated 56-sol blocks allow measurements to be compared over equal elapsed intervals. The unavoidable remainder is then concentrated in a shorter final month.

The underlying choice is:

equal orbital progression

versus:

equal elapsed civil duration

Marian gives the civil calendar greater elapsed regularity and leaves precise seasonal position to Ls. It therefore does not ask the month to become an ephemeris.

F.6 The week problem

Levitt, Darian and Marian all accept a break in the uninterrupted weekday-label sequence in order to preserve tightly bounded civil years, fixed month starts and recurring date–weekday identities.

No physical sol disappears.

The discontinuity exists in the civil weekday sequence.

Šurán demonstrates that this is not the only possible choice. A whole-week intercalation approach can preserve uninterrupted seven-sol succession because the correction itself occurs in complete seven-sol units. A representative form considered in the manuscript uses civil years of:

96 × 7 = 672 sols

and:

95 × 7 = 665 sols

A suitable sequence can preserve the long-run average, but individual years sit farther from the approximately 668.6-sol Martian astronomical target than Marian's 668- and 669-sol forms.

The comparison therefore does not reveal one system solving the week problem and another failing to do so.

It reveals two different placements of the same inconvenience:

Šurán protects continuous weekly succession by allowing larger whole-week variation in civil-year length.

Marian protects tightly bounded civil-year length and recurring dates by allowing selected terminal weeks to contain six weekday positions.

F.7 Exodus and the interface problem

Exodus makes another design choice unusually visible: familiarity has value.

Its use of January through December and familiar weekday language reduces the amount an Earth-born settler initially has to learn. That is a genuine human-factors benefit rather than a cosmetic concern.

The corresponding risk is false equivalence.

An Exodus January contains 56 sols. The word is familiar, but the interval is almost twice as long as the January an Earth-born user already understands.

Marian takes a slightly different interface position. It retains recognisable ancestry — Janiix, Monsol and so forth — while modifying the terms enough to signal that the underlying unit has changed.

Neither choice can be proved correct mathematically.

The relevant question is whether greater recognition or greater signalling of difference produces fewer human errors in actual use.

That remains an empirical question.

F.8 Where Marian sits

Marian is best understood historically as a composition rather than an isolated invention.

Its twelve-month 56–56–55 macrostructure has clear Levitt precedent. Its approximately four-week minth occupies the same scale that Darian makes primary. Shortened terminal civil weeks have precedent. The concern with familiarity is shared with Exodus. Zubrin and Hargitai make especially visible the difference between orbital representation and elapsed-time regularity. Šurán demonstrates that even the location and scale of intercalation are design variables rather than facts imposed by Mars.

Marian's distinctive claim is therefore deliberately narrower.

It is not that twelve long Martian months are new.

They are not.

It is not that approximately four-week Martian periods are new.

They are not.

Nor are shortened weeks, astronomical anchoring, perpetual recurrence or concern for familiarity.

The distinctive move is primarily composition and assignment of function: twelve months provide annual orientation; twenty-four minths provide short cadence; six Sixths provide an intermediate civil horizon; four quarters retain the annual fraction; Ls remains available for precise seasonal position; and the calendar's civil and machine identities are deliberately separated from its replaceable human vocabulary.

That is why comparison with earlier work strengthens Marian rather than weakening it.

The calendar does not depend upon pretending its ingredients have no ancestry.

Its proposition is that those ingredients can be assembled coherently around a particular brief:

a permanent, technologically complex, still Earth-connected Martian civilisation requiring several stable civil horizons without asking one inherited unit to perform every job.

F.9 Reading the comparison correctly

This appendix should not be used as a scorecard.

Different users can rationally weight the same properties differently. A climate scientist may place unusual value on equal elapsed intervals. A community for whom an uninterrupted seven-day religious cycle is fundamental may reject any shortened-week system outright. Early migrants from Earth may place greater value on familiar vocabulary than people born on Mars generations later.

Astronomy can determine whether the arithmetic works.

It cannot decide those priorities.

The history of Martian calendrics therefore provides an important conclusion rather than an embarrassing lack of consensus:

there is no uniquely correct civil calendar hidden in the orbit of Mars.

Mars supplies the physical constraints.

A civilisation still has to decide what it wants its calendar to do.