ORBIT
6) The Calendar for Worlds
Astronomical Orbiting Time

The human side of Solarian is deliberately portable. A week remains a week, a minth remains a human-scale operating period and twelve minths make one mear whether somebody lives on Mars, Ceres, Titan or inside an artificial habitat.

The astronomical side is deliberately local.

Every inhabited world or planetary system occupies a real position around the Sun and follows a real heliocentric orbit. Solarian preserves that astronomical identity through a second calendar running alongside the human one:

PEOPLE
12 minths = 1 mear

PLANET
12 orbital months = 1 year

The distinction is fundamental. The people calendar tells us where we are in the human operating cycle. The astronomical calendar tells us where our world is in its orbit.

Its governing principle is:

The year belongs to the orbit and planet.

Twelve months, one orbit

Every Solarian astronomical calendar divides one local heliocentric year into twelve numbered orbital months:

1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9 → 10 → 11 → 12 → 1…

Month 1 begins the local orbital year, Month 6 places the world around the middle of that annual sequence and Month 12 tells us that the next local New Year is approaching.

The important point is that an orbital month is defined by its position within the local year, not by a familiar duration in days or weeks. On Earth, one-twelfth of an orbit happens to resemble what humans already think of as a month. On Mars it lasts considerably longer, a Jovian orbital month is roughly an Earth year in scale, while a Neptunian one extends for well over a decade.

All remain months in the Solarian sense. Their job is not to provide a human planning interval. Their job is to describe progress through the local orbit.

That is why Solarian uses the word year equally precisely:

1 local year = 1 heliocentric orbit

A Martian year is therefore not a 365-day Earth year with different names attached, and a Saturnian year is not an inconveniently stretched terrestrial one. Mercury completes its year in about 88 Earth days, while Neptune requires roughly 165 Earth years.

Neither creates a conceptual problem because the astronomical year is no longer being asked to provide the human operating rhythm as well.

The mear does that job.

The distinction Earth hides

Earth makes these two calendars harder to distinguish because its astronomy happens to be unusually accommodating. The terrestrial orbital year sits near a timescale humans find useful for education, budgeting, age, sport and planning. One-twelfth of that year also falls reasonably close to the human-scale period we find useful for medium-term organisation.

So on Earth:

mear ≈ year

and:

minth ≈ month

Those near-overlaps are convenient.

They are not universal.

Mars begins separating the two scales, while the outer planets pull them dramatically apart. Venus and Mercury reveal the same distinction from the opposite direction because their orbital years become shorter than the human operating cycle we want to preserve.

The useful rule is therefore simple:

A minth is human-scale. A month is orbit-scale.

An orbital month does not need to feel like a terrestrial month to perform its job.

A common reference notation

Solarian gives every orbital month the structural identity 1 to 12, but it also provides a compact shorthand for situations where calendars from several worlds appear together.

The notation combines the familiar abbreviated terrestrial month stem with a three-letter identifier for the relevant world or planetary system.

On Mars:

Janmar · Febmar · Marmar · Aprmar · Maymar · Junmar · Julmar · Augmar · Sepmar · Octmar · Novmar · Decmar

In the Saturnian system:

Jansat · Febsat · Marsat · Aprsat · Maysat · Junsat · Julsat · Augsat · Sepsat · Octsat · Novsat · Decsat

So Janmar simply means Martian Orbital Month 1, while Julsat means Saturnian Orbital Month 7.

These are reference labels, not proposed local month names. Future Martians, Saturnians or Cererians may develop entirely different cultural names and use them almost exclusively in ordinary life. The numbered month and its Solarian reference label simply remain underneath as the common cross-world identity.

Solarian standardises the identifier.

It does not attempt to standardise the poetry.

One twelve-position orbital clock

The easiest mental model for the astronomical calendar is a twelve-position clock centred on the Sun. Imagine each world as a hand moving around the same clock face. One complete circuit is one local year, while the twelve labelled positions provide a coarse civil description of progress around the orbit.

The hands move at radically different speeds. Mercury races around the dial. Earth moves at the rate familiar to us, Mars more slowly, while Neptune advances so gradually that a human lifetime occupies only part of one circuit.

The twelve positions still mean the same broad thing.

That requires the clocks to share an orientation.

Solarian therefore gives every orbital calendar the same heliocentric reference direction:

λ₀ = 100°

The technical specification defines that direction precisely. The useful mental model is simpler:

Every Solarian orbital calendar uses the same underlying twelve-o'clock direction, aligned to Earth's traditional Gregorian New Year reference.

Imagine looking down on the Solar System and drawing one fixed line outward from the Sun. When a world passes that reference direction it begins its local astronomical year, after which Months 1 through 12 describe its progress around the orbit until the cycle repeats.

The worlds do not reach those positions together.

They simply share the same orientation.

That makes Month 1 on Mars structurally comparable with Month 1 around Jupiter or Saturn even though those months occur at different times and last radically different durations.

This is not a navigation system. A Solarian orbital month provides only a coarse civil description of orbital position, in much the same way that saying “mid-March” gives a useful sense of Earth's annual position without pretending to replace an ephemeris.

The astronomical calendar gives the orbit a human-readable face.

The orbit is continuous; the calendar is discrete

There is one technical distinction worth establishing before we go further.

A physical orbit is continuous. The world moves around the Sun without regard for the boundaries humans later draw through that motion. The Solarian civil orbital year is our discrete calendar representation of that continuous physical cycle.

Those two things are closely related, but they are not identical.

In synchronized Solarian implementations, the civil calendar is constructed from complete weeks and kept closely aligned with the underlying orbit over time. The mechanism for doing that comes later.

For now, the important distinction is:

The orbit is continuous. The civil calendar is discrete.

One belongs to physics.

The other is our civil representation of it.

Planetary systems share their year

The distinction between local cycles becomes particularly important around the giant planets. Ganymede, for example, rotates, orbits Jupiter and travels around the Sun as part of the entire Jovian system. All of those physical cycles can matter, but they do not need to become competing civil years.

Solarian therefore normally gives natural satellites the astronomical calendar of their parent planetary system. The major Jovian moons use the Jovian year. Titan and Enceladus use the Saturnian year. The major Uranian moons use the Uranian year, Triton the Neptunian year, Earth's Moon the Earth year, while Phobos and Deimos use the Martian year.

The rule is:

The civil year follows the heliocentric planetary system, not the moon's local orbit around its parent.

A moon's own orbital cycle remains available wherever it matters operationally — for illumination, transport, eclipses, radiation or other local purposes.

It simply does not need to become another competing civil year.

Artificial worlds can belong too

The word planet is useful shorthand, but Solarian does not actually require one.

A permanent artificial habitat travelling independently around the Sun also possesses a real heliocentric orbit. It can therefore possess a real orbital year and use the same twelve-month astronomical architecture. Its gravity might come from rotation, its light-dark cycle might be artificial and its human civil day might be the standard 86,400 seconds.

None of that changes its path around the Sun.

A habitat operating closely within a planetary system may instead inherit that system's astronomical calendar, just as a natural moon does.

The distinction remains the same:

the civil day belongs to human cadence; the year belongs to heliocentric orbital identity.

Where the orbital clock becomes imperfect

The twelve-position model works most naturally on orbits that are reasonably close to circular. Real orbits are not perfect circles. A body on an eccentric orbit moves faster near the Sun and more slowly when farther away, so equal periods of elapsed time do not always correspond neatly to equal angular movement around the orbit.

For low and moderate eccentricities, the standard twelve-part civil representation remains a useful approximation of orbital position. At sufficiently high eccentricity, it may not.

That does not break the human operating calendar. It simply means the standard astronomical layer has reached one of the applicability limits required by the design brief.

We will encounter that problem properly when we reach Pluto and some of the more eccentric small worlds.

Twelve and twelve

We now have the two basic Solarian calendars side by side:

PEOPLE
12 minths = 1 mear

PLANET
12 orbital months = 1 year

The first provides a recurring human operating rhythm. The second describes the local world moving around the Sun.

At this stage they remain conceptually separate.

The next question is whether there is a simple relationship between them.

In many parts of the Solar System, there is.

One number tells us how many minths fit within an orbital month and, equivalently, how many mears fit within the local orbital year.

Solarian calls that number the Repeat Factor.