One of the things about sci-fi games that span multiple worlds is that each world has its own length of year and length of day that impact the way the planet operates. And while I’ve been pretty good about initially describing it for the worlds my on-line game has been set in, I’ve not been very good about keeping track of it during actual play.
I got to thinking about this some more as I was working on the Frontier Timeline. I needed an entry for a blank day and decided to make it the birthday of a notable person in the Frontier (Crown Princess Leotia Valentine Leotius of Clarion). And that got me to thinking about the time keeping on that planet.
Another thing that came out of this is the realization that so far, I’ve only really looked at this on planets that have really slow rotation periods. My online game has so far taken place on Pale in the Truane’s Star system which has a rotation period of about 55 hours and on Laco in the Dixon’s Star System which has a rotation period of about 60 hours. Clarion’s is 50 hours, 5 minutes. Which is funny to me since the length of a “Galactic Standard” day is only 20 hours. Maybe some day I’ll work on a system with a period close to that.
So this post is going to talk both about Clarion’s calendar and also about how I went about calculating it. We’ll start with what we know from published materials and work our way to a final calendar.
Stellar Data
From both the Expanded Game rules and the Warriors of White Light module, the star is described as a yellow-orange star. Zebulon’s Guide gives it a spectral type of F7 but that is a yellow-white star not a yellow-orange one. Yellow-orange would give it a spectral type of late G or early K so from notes I have in other places, I’ve assigned White Light the spectral type of K1.
This means that the star is about 72% the mass of our sun. The exact value I assigned is .72155 solar masses (actually I took it to a few more decimal places) or 1.43516×1030 kg.
Orbital Data
Orbital Distance
In the Warriors of White module there is this image of the White Light system:
Based on the scale on the image I estimated that the orbital distance of Clarion was about 93 million kilometers (for reference the Earth is about 150 million km from the sun). This makes sense for a K1 star that is less luminous than the Sun as a habitable planet would have to be closer. The exact value I gave for the semi-major axis of the orbit was 93,027,587 km. That was generated by simply rolling six d10s for the digits after 93. Had the first digit not been low, I might have rolled a d4-1 but I actually rolled a zero so I was happy.
Orbital Period
Now that we have the mass of the star and the orbital distance we can calculate the orbital period of the planet. This can be done simply by applying Newton’s form of Kepler’s Third Law of planetary motion:
Where we have the following:
- P = the planet’s orbital period
- a = the semi-major axis
- G = the gravitational constant
- M1 = the mass of the star
- M2 = the mass of the planet (which we’ll ignore here as it is about half a million times smaller than M1)
Plugging everything in in the correct units (left as an exercise for the reader) we get that the orbital period of Clarion around White Light is 5059.77 hours. This means that the “year” on Clarion is just under 253 Galactic Standard days; significantly shorter than the 400 Galactic Standard days in a Galactic Standard year (which is only ~91.3% of an Earth year). Compared to Earth, the year on Clarion is only 211 days long, about 58% of our year.
But we’re not quite done yet as we need to calculate that in terms of the local day.
Rotational Period
This one is easy. The Warriors of White Light module says that the rotation period of the planet is 50 hours and 5 minutes, with is just a little more precise than the 50 hours given in the Expanded Rules and Zebulon’s Guide so we’ll go with that number. I’m just going to leave it as is and not add any extra seconds on to it.
So if we take that value, it turns out that Clarion rotates 101.027 times every year. Or said another way, the year is 101.027 local days long. The fact that it was almost an integer number of days was a happy coincidence. I did not try to make that happen. I was pleasantly surprised when it did.
The Calendar
Okay, now we have everything we need to get the calendar set up. Well, almost everything. There is one more bit we need to do.
Clarion was settled by humans. Who we assume are somewhat like us Earthlings in that they work better on a 20-25 hour day than a 50 hour one. When the humans landed on Clarion, the decided to simply divide the long 50 hour diurnal period into two 25 hour days. They deal with the extra 5 minutes by adding in an hour the “night” period every 12 days and most people get a little extra rest that night.
Each of these 25 hour day periods are divided into a “day” period and a “night” period even though it may or may not be light or dark as one would expect by the name. Like the locals on Laco, they refer to the periods throughout a single diurnal cycle as “day-day” and “day-night” when the star is up and “night-day” and “night-night” when the star is down.
With this set up, there are 202.054 days in the year. They break it down as follows. (From here on out, unless specified, the term day refers to one of these 25 hour periods).
- 1 week = 8 days (4 diurnal periods)
- 1 month = 20 local days (10 diurnal periods)
- 1 year contains 10 months with two special holidays occurring mid-year (between months 5 & 6) and on the last day of the year.
- The mid-year day is Observance Day, set aside to remember and commemorate all those who have sacrificed for the survival and safety of the planet.
- The end year holiday is Landing Day, commemorating the day the original settlers landed on the planet. In many ways it is also a celebration of the ruling Leotus family and is often the day for coronations of new monarchs or other events related to the ruling family.
- Every 37 years, that 0.027 of a local day catches up with the calendar and they have a leap year. On that year, they add an extra day to both Observance Day and Landing day making each a 2 day holiday. The next such occurrence of the Clarion leap year occurs during FY 69.
Reckoning Age
One impact of the calendar is that people have a lot of birthdays. Because of the very short local year, and the fact that the rate that the settlers grow and mature is similar to us here on Earth, people on Clarion mature much slower than their “age” would indicate. A 16 year old Clarionite is only 9.25 Earth years old. You probably shouldn’t give them the keys to the hovercar.
Because of this, the early settlers established the age of 35 (in local years) as the age of majority on the planet. This roughly corresponds to someone that is 22.13 Galactic Standard years old (or 20.2 Earth years old). There has been a bit of a push in recent years to lower this to 30 local years but the movement has not gained much traction.
Crown Princess Leotia
Which brings me back to what started all of this in the first place – Crown Princess Leotia’s birthday. The Warriors of White Light module contains this little tidbit:
The current king, Leotus XIX, has ruled for 37 years and soon will no doubt abdicate in favor of his daughter, Leotia XX.
If you’re following along with my #SFTimeline posts on Twitter, and reading this on the day the post publishes (Jan 15, 2019), I’m going to spoil a timeline entry for next week:
FY60.017 – Leotia Valentine Leotus, crown princess of Clarion (White Light), celebrates her 32nd birthday (18.5 earth years) #SFTimeline
I’m taking the “soon” in the quote from the module to be within the next decade or so (GST) and have decided that it will probably occur during the 2-day Landing Day celebration in FY 69. I also want Leotia to be young but she will have had to reach her majority by then. So I decided that she is about to celebrate her 32nd birthday.
The abdication might have occurred sooner but by the time Leotia reaches her majority (which will occur on FY61.375, the Second Sathar War will be in full swing and Leotus XIX doesn’t feel that she’s quite up to that task at her young age and so decides to wait until the big celebration in FY69.
Final thoughts
I had a lot of fun working this out. I’ll probably be doing it for more of the Frontier worlds in the future, again probably tied to trying to tie a series of local events into my timeline project. Although I may go do Pale and Laco first as part of my game background.
Have you ever done this for any of your worlds? Do you think it adds to the verisimilitude of the game or is it just too much of a hassle? Is there anything I didn’t explain to your liking? Share your thoughts and ideas below.