
How does the Kerbal calendar work? How longs are weeks or months? Doing an airship flight to the temple of Tut-Ur Jeb-Ahn has me thinking about how those conventions might have established themselves.
Astronomically, I think it would be munar, based on the orbits of the Mun and Minmus, and, with the rough times of the Mun’s orbit being a little over six days and Minmus’ orbit being almost 48 days, that would very easily define weeks and months respectively. A six day week compared to the human 7 day week and the 48 day month compared to the 30 or 31 day earth month is intuitively comparable.
But the detailed math is a little more tricky.
The Kerbin year is 426 days, 32 minutes, 24.65 seconds (9,203,544.65 s)
The Kerbin solar day is 6 hours exactly (21,600 s).
However the calendar is divvied up, there will need to be a leap day added every 12 years.
The Mun’s siderial period is 6 days, 2 hours, 36 minutes, 24.377 seconds (138984.377 s), that is, how long it takes to go 360 degrees or once around based on the assumed infinitely distant background stars. But, and this is the thing, you would need to be an astronomer to have worked this out. Carefully watching the skies and measuring the Mun against the background stars. Kerbin, however, orbits the sun with zero inclination and the Mun orbits Kerbin with zero inclination, leading to a solar eclipse every time the Mun goes around Kerbin. And because Kerbin will have moved in it’s orbit a little bit compared to where it was at the beginning of the Mun’s orbit, the time eclipse to eclipse would be based on the Mun’s synodic orbit, which is 35.51705 minutes.
I think. This is a bunch of math and I’m not sure I’m doing it right. I have also seen people out on the web doing similar math and getting slightly different answers. I’m just going to keep going and while I am taking my math out to multiple decimal places, when I get to the end and finalize the calendar, I think these numbers will come back down to integers.
Anyway, back to the math.
The Mun’s synodic period (from the Wiki) is 141,115.4 seconds. That’s 6.53312037 days. Every six and a half days, the Mun passes in front of the sun in a total solar eclipse.
You don’t need to be an Kerbal astronomer to see that. Everyone will see it. Well, not exactly. At six and a half days the next eclipse will happen on the other side of Kerbin. A ancient kerbal peasant or shepherd living in one place will see the next eclipse when it comes around again six and a half days after that (and almost 24 minutes later in the day). Their “week” might naturally settle out to 13 days. Eclipse to eclipse.
To us humans playing in the kerbal world, having a 13 day week won’t be intuitive so let’s go back to the shorter timeframe. And, to keep the calendar closer to the astronomical occurrences, one defined week will be 6 days and the next will be 7 days. Alternating through the year.
Minmus has a synodic period of 1,220,131.7 seconds or 56.4876 days. Divided into the year, this might sort itself out to there being seven and a half months. That’s a lot of days left over but, if we want to try to get the calendar closer to what’s going on in the sky, we can double that, like we did for the “week” and have 15 months of 28 days each and then only 6 days left over.
Then, to even that out, we need to place those extra days. What I think works best is to have 9 months of 28 days and 6 months of 29 days set out in a pattern of 28, 28, 29, 28, 29 that repeats three times over the year.
Kerbin does not have any axial tilt and so the idea of “seasons” as they are on a tilted Earth would not apply but these three repetitions of the monthly format breaks the year into Early, Middle, and Late.
As to week and month names, this would be all speculation and personal preference. The Internet already has several versions proposed.
The “Western” week is mostly based on Nordic gods, which were probably based on the Roman and before them Greek gods, each associated with the visible planets (and the sun), overlaid onto days of the week. To keep with my ancient astronomers trend, there would be 7 objects visible in Kerbal skies; the sun, the Mun, Minmus, Moho, Eve, Duna, and Jool. I should think Dres and Eeloo to be too small and too distance to be visible with the naked eye. Days of the week would map Kerbal “gods” perhaps associated with each of those bodies onto the 6 days of the week with the Sun-day occurring every other week. Munday? Senul (Moon in backwards Spanish)? Again, back to personal preference.
And the names of the month would be even more up to preference. Many human months are based on numbers, for example, December translates out as the “tenth month” but isn’t actually the tenth month because months honoring a few Roman emperors got squeezed in there. Plus, the Romans threw some other differences in. Other calendars have their months named after star constellations, adjusting the intuitive lunar calendar into a non-shifting solar calendar. The Baha’i’ calendar names its months after the attributes of God. Some calendars use month names to identify changing seasons, specific holidays, highlight moral codes, tasks like planting or harvesting, and pretty much anything else that changing history and language can lead to.
There are Internet suggestions out there but I don’t think any of them have as many as 15 months.
So, to summarize.
The Kerbin year is 426 days.
The Kerbin year adds a leap day every 12 years.
The Kerbin week alternates with either 6 or 7 days.
The Kerbin year has 15 months.
The Kerbin month has 4 full weeks plus 2 or 3 additional days.
The Kerbin seasons have 5 months each.
The Kerbin month has either 28 or 29 days with a repeating pattern of 28, 28, 29, 28, 29.