# Europan Clock and Calendar

Ron Hale-Evans

This is a proposed timekeeping scheme for Jupiter's moon, Europa.

I wrote in my book Mindhacker, "Of course, time is time everywhere, but one of the surest ways to vault out of Earthly timekeeping considerations — and thereby gain a wider viewpoint — is to develop a clock and calendar for another world. As Lance Latham points out, because you can’t rely on comfortable Earthly constants like 365, 24, and 60, developing a calendar for another planet can be a self-test for understanding calendrical concepts... why not try designing a calendar for Saturn; one of the moons of Jupiter, such as Europa; or the asteroid Ceres?"

I took my own advice and developed this timekeeping system. Because it has an ocean of water, Europa is one of the more likely spots in the solar system to have developed life, so one day, humans may establish a scientific base there. This system was developed against that day. I'm not vain enough to believe such explorers would actually use my clock and calendar, but they were fun to imagine.

I am working on incorporating this system into OffBeat.

## The basics

Jupiter orbital period = 11.8618 y = 4332.59 d

Europa orbital period = 3.551181 d = 3 x 1.18 d

1.18d = 28.408 h ! (euday) = one 28-Hour Day, plus 24.48 min (.408 h = 24.48 min)

euweek = 2 orbital periods = 2 x 3 = 6 eudays

6 x 1.18 d = 7.08 d

4332.59 d / 7.08 d = 611.95 (612) euweeks

612 euweeks / 12 euyears = 51 euweeks / euyear

So…

• 1 Jovian jyear = 12 Europan euyears (a dodecade)
• 1 euyear = 13 eumonths = 51 euweeks
• 1 eumonth = 4 euweeks (the 13th eumonth has only 3 weeks)
• 1 euweek = 6 eudays = 2 Europan orbital periods
• 1 euday = 28 hours, 24.5 minutes

## How to notate dates

jyear.euyear.eumonth.euday.hour.minute

Zero-based. Jupiter epoch J2000 = 2000 Jan 1.5 TT. Don’t use Europan epoch; it conflicts with Jupiter and is non-standard.

## To do

• Name months after imaginary alien animals, such as tribbles, in alphabetical order.
• Name euyears of a dodecade after something else.
• Calculate current date! Write a computer implementation.