Darian (Io)

Overview

The Galilean Darian calendars are calculated calendars created by Thomas Gangale for use on the four Galilean moons of Jupiter---Io, Europa, Ganymede, and Callisto. They are intended to loosely align with the Mars-based Darian calendar, roughly sharing an epoch as well as all 24 months.

The inner three moons are in a 2:4:8 Laplace resonance, and thus their orbits and solar days are in nearly exact ratios. As the solar day of Io, the inner-most moon, is over 42 hours, its day is broken into two units of time called 'circads' that are ~21 hours each and act as calendar days. The remaining moons have their orbits broken up into similar-sized circads: 4 for Europa, 8 for Ganymede, and 19 for Callisto.

The calendars all share circads, months, and weeks of 8 circads, though they drift in and out of phase with each other depending on intercalation. Generally months have 32 circads, with few exceptions, most notably the final month that can be intercalated to have 24, 32, or 40 circads. The months are also prefixed with a shorthand name of the moon.

Info

All four of the Galilean Darian calendars use roughly the same epoch, within a week, as the Martian Darian calendar, each of which corresponds with their Meridian Time.

Accuracy

The accuracy of this calendar system is wholely dependent on the writings and calculations of Thomas Gangale. It is likely that these calculations weren't precise enough to extend more than a few decades, as they do seem to drift from ephemeris data.

The epoch is noted to account for the time it takes light to travel from Jupiter.

Source

This formula was extrapolated from the writings of Thomas Gangale found at this website.

It can be somewhat calibrated using this model if you know what you're doing.