The Centran Calendar System

Hey everyone, this week’s Patreon BTS post comes from our Sojourn Science Advisor Gabriel Fonseca, where he’s delving into the Centran Calendar system, enjoy! - Dan

After I was brought in to work in The Sojourn, one of the first things I did was set about fleshing out the worlds of the Tantalus Cluster. Most important of them, however, was Centrum - humanity’s homeworld in our universe. Dan had already created a basic outline of what he wanted for the Centrum System - an Earth analog with two moons, a Mars-like world, a single, colossal gas giant… and all of them would be orbiting a blue star.

That was an interesting challenge. Blue stars are more massive and brighter than our sun, so as a result, Centrum would not only need to orbit further from it, but also have a different orbital period than that of Earth. I made Solaris as blue as I could without stretching believability past its breaking point, and we ended up with a star about 20% more massive than the Sun and nearly four times as luminous.

While messing with the numbers, I noticed that when placed to receive an Earth-like insolation from its star, Centrum ended up with an orbital year of about two Earth years - and doing what I do, I got carried away and started thinking about what kind of Calendar the people of this world would have - this eventually became the Centran Calendar as we have today.

We knew before we even started doing our (literal) world-building that, for narrative convenience, we wanted to keep time measurements in Centrum more or less the same as those of Earth - so seconds, minutes, hours and days would all be the same between Earth and Centrum. Knowing that and the length of a Centran year, I set about figuring the calendar out.

As mentioned before, due to an incredibly happy, unplanned coincidence, Centrum takes almost exactly 2 years to spin around Solaris. For narrative reasons, we decided that the Centran Calendar (PCU) should be immediately intuitively understandable to our audiences. As such, it was decided that instead of counting the passage of time based on the time it takes for their planet to spin around their star, Centrans would count the time based on the passage of the seasons: Summer and Winter, with the reasoning that their long duration (368 days each) meant that they would have played a crucial role in the livelihood of Centran societies, even more so than on our own.

Originally, we had made it so that under this system, an “year” on centrum was always two Seasons - and thus two Earth Years long. As Dan kept confusing himself in his usage of Years and Seasons as originally specified, however, eventually we would change this nomenclature at his request, and make it so that “years” and “seasons” are both interchangeable terms, both meaning “368 days”. (I here completely disavow myself from any responsibility for the confusion this may ensue.)

Having figured all that out, it was time to make the calendar more granular. Yes, sure, years are all cool and good, but we don’t normally tell the passage of time by saying “we’re 23.6% of the way into the year”, after all - so it was time to figure out months.

Earth’s Months are largely governed due to the cycle of the Moon - our calendar is a Lunisolar one, which tries to use both the movement of the Sun and Moon to keep track of the passage of time. Given that it is a near miracle that our actual, real-world calendar system even works at all, I didn’t even bother trying to make the Centran Calendar be Lunisolar. It is, instead, purely solar, and as a result, the Centran Calendar lacks what we would normally consider “months”. But in its stead, it has two large divisions of a given Season/Year: the Equinox and Solstice.

The Equinox is commonly defined as the moment the plane of the equator passes through the geometric centre of the sun - and thus, it marks the day where all over the planet, the day and night are of the exact same length. Given it is functionally both the end and start of the seasonal cycle, the Centran Calendar uses the first day of Equinox as the first day of a Year/Season.

The Solstice, conversely, is commonly defined as the moment when the sun reaches its farthest distance from the equatorial plane in the sky - and also the day when sunlight lasts the longest, if summer, or shortest, if winter. It can be considered the “apex” of a given season, and as such, marks the middle point of the Centran Season/Year.

In the Centran Calendar, both the Equinox and Solstice last the same amount of time, 184 days each. The sole exception to this is the Leap Year, which happens once every 48 years to compensate for the fact that Centrum whirls around Solaris once every 735 days and twenty-three hours. During the Leap Year, a single extra day is added to the Solstice, creating the infamous 185th of Solstice. (If you thought people born on February 29th had it bad...)

Not wanting to forego the ability to use “months” without causing a lore maelstrom, however, after having finished the Centran Calendar I eventually forced myself to sit down and figure out how months could have worked on Centrum. As a result, we created a calendar that used a Lunar scheme, using the cycles of Lysane and Lysara to track time. Those calendars did have 12 months to a year, where the months were four cycles of 31-31-30 days long each. Nowadays however, a “month” is considered an antiquated, albeit still sometimes useful, artefact of old Pre-Unification calendar systems, something akin to a “Fortnight” in our real world.

So, to round this all up, we leave you with this handy cheat-sheet we use internally, that sums the mess above in a simple, straightforward format:

Fair Winds!