Ganymede Meridian Time

Overview

Ganymede Meridian Time is a measure of time passed since midnight on the prime meridian of Ganymede, moon of Jupiter.

It features a similar 24-hour clock to Earth time, but the units are about 11.5% shorter. One Ganymede solar day is about eight Earth days, so the day is further broken up into eight circads of 21 hours each.

Ganymede is tidally locked with Jupiter, meaning one side of the moon always faces the planet and the other side always faces away. The prime meridian is determined to be the meridian on the moon's surface that is facing directly at Jupiter.

Midnight is thus the time when the moon is directly between Jupiter and the sun, though this is only used as an epoch for the beginning of the first circad in each solar day. The fifth circad happens when the moon is on the opposite side of Jupiter from the sun.

Ganymede Meridian Time is a name that was chosen for this website and might not be accurate.

Info

Ganymede is in a 2/4/8 Laplace resonance with Io and Europa, so their solar days are equally comprised of 2/4/8 circads, though the length of their circads are very slightly different. The circad of Ganymede is 21.49916 Earth hours long, which is then broken into 24 Ganymede hours.

As the orbit of Ganymede is not very inclined, midnight on Circad 1 is also roughly the time of a total solar eclipse on Jupiter.

Accuracy

The accuracy of this timekeeping 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.

The name of this timekeeping system is my own creation, as Mr. Gangale did not give it a name himself.

Source

All of the information on this calendar came from its Wikipedia article.