Saturday, September 24, 2011

A Calendar for the Moon of 55 Cancri f

A while ago I was making plans to write stories in the world of Esperanza, a fictional habitable moon of 55 Cancri f, a gas giant that's known to orbit within the habitable zone of its star. I made a fair amount of early progress before I discovered more detailed plots of f's orbit that demonstrated its orbit was a bit more eccentric than I'd thought; that the planet spends roughly a quarter of its orbit inside the habitable zone.

If it had been otherwise, if the orbit had wandered out of the HZ for a spell, that'd be different; it's easy to retain heat, but it's a bit more difficult to get rid of it, and while the limited calculations I did indicated that it wasn't out of the question for liquid water to exist on one of f's moons no matter what the nature of the planet's orbit, that moon would be way too torrid for humans - the numbers I found were in the neighborhood of 70 or 80 degrees Celsius, though I freely admit there's every possibility that I screwed up the math and the real situation is entirely different. I am, after all, a dude that very nearly failed Grade 10 General Math.

Before I found these things out, though, I'd put together a calendar, after the Coyote series demonstrated the need for one. Since planets don't tend to share orbits, it's unlikely I'll be able to use it as I've put it together, except for some built-to-specs fictional planet. So here it is.

The Calendar of 55 Cancri f-I (Esperanza)

While the telescopes we have are sensitive as hell, and have to be in order to detect all these exoplanets, there's still room for uncertainty. To my knowledge, 55 Cancri f's orbital period still isn't exactly known; but Wikipedia cites a 2007 article that makes it 260 days, plus or minus 1.1, so I just split it down the middle and gave it a 260-day long year. That's one of the things I liked about it; a lot of other planets seem to have years that are longer than Earth, so it felt fresh and new for the years to go by quickly.

The moon, Esparanza, has its own day; it's not tidally locked to the gas giant for valid reasons that are irrelevant here. That day is thirty-eight hours long, which makes the local year 164.2 E-days in length, with the decimal resulting in there being an extra 7 hours and 36 minutes left over at the end of the year. Originally I'd planned to have them constitute a "short day" after the last regular day of the year, but I didn't think that would work; it seemed to me it would make the sunrise and sunset times gradually drift.

Esparanza orbited 55 Cancri f with a semimajor axis of roughly 1.6 million kilometers (I'm working off of memory with this point, but hopefully the number is accurate), making one orbit in 15.7 days. This worked out well for making the standard month sixteen days long. There are nine months on Esparanza, which I named after the Muses of Greek mythology plus one: Mnemosyne, Polyhymnia, Erato, Clio, Thalia, Terpsichore, Euterpe, Melpomene, and Urania. Mnemosyne is a twenty-day month; all the others have sixteen days. New Year's Day, Mnemosyne 1st, is Esparanza's northern hemisphere Winter Solstice.

Yet there's still the issue of those leftover hours and minutes at the end of the year. After a bit the solution was obvious - just use a leap year. After five years, enough spare time has piled up at the end of the year to be worth a day in itself; this day occurs on Terpsichore 17th, and in accordance with the Law of Fives, it is called St. Tib's Day.

There are four days of the week, with names derived from the classical Japanese elements: Tsuchiday, Hiday, Kazeday, and Mizuday.

So here's what a page of a calendar would look like:


In-setting, the Esparanza calendar began with its original discovery from Earth in 2042, which allowed me to calculate backwards to determine the importation of holidays. Figuring out the date that, say, Christmas or Easter would fall on is an issue for people more focused on calendrical affairs, though now that I think about it that could make an interesting background for a short - I went with something simpler, and figured out the date on which Esparanzans would celebrate X-Day.

Fairly simple - X-Day, the prophesied end of the world at the hands of the alien X-ists and Sex Goddesses, happened on July 5, 1998. (What, don't you remember?) Converting the Earth and Esparanza years into hours, I worked backward and found that July 5, 1998 and March 17, 2042 - this latter date being Mnemosyne 1st, O AS (Anno Spes, as "spes" and "esparanza" both mean "hope") - were separated by exactly 383,064 hours, going from midnight to midnight. Thus, July 5, 1998 worked out to Clio 12th, -61 AS, and I had a yearly Esparanzan date for X-Day. Truly an important holiday to pin down.

Then science came and wrecked it all up, and I packed up for some new star system. Still - I like the way this one was starting to come together.

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