Galilean (Callisto)
| Epoch | Confidence |
|---|---|
| 28 December 2001 +12:27:23 | Medium |
Overview
The Galilean 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 Earth-based Gregorian calendar, roughly sharing an epoch and most month names.
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. There are 13 months, with the 'extra' month of Mercedonius added between the February and March analogs. Generally months have 32 circads, but Ganymede's Junius is only 24 circads, as well as the month of December for all moons in non-leap years. The months are also prefixed with a shorthand name of the moon.
Info
All four of the Galilean calendars use roughly the same epoch, within a week, as the Gregorian calendar, each of which corresponds with their Meridian Time.
The Galilean months are roughly equal to the Gregorian months, though with slightly different names as well as a 13th month added between Februarius and Martius. Each moon has a slightly different day arrangement.
| Callisto Month | Circads |
|---|---|
| Cal Januarius | 32 |
| Cal Februarius | 32 |
| Cal Mercedonius | 32 |
| Cal Martius | 32 |
| Cal Aprilis | 32 |
| Cal Maius | 32 |
| Cal Junius | 32 |
| Cal Julius | 32 |
| Cal Augustus | 32 |
| Cal September | 32 |
| Cal October | 32 |
| Cal November | 32 |
| Cal December | 24-32 |
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.
I was unable to properly understand the intercalary system employed by Mr. Gangale, so I introduced my own while attempting to match his intent as closely as possible.
The name of this calendar was only implied in the original text but never explicitly stated.
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.