Designing a Better Calendar for Earth

i bought myself a planner with unnumbered days, so then i had to number them. but i would have felt wrong filling in the stupid month and day numbers from our standard calendar, so i ended up designing my own calendar system. just for funsies.

1 - planner

the Gregorian calendar is stupid

  • we almost never know what day of the week any date is, which is a confusing pain in the ass that we’ve all just gotten used to. this is because the months are different lengths, and every year starts on a different day of the week.

  • “months” supposedly correspond to moon phase cycles, but Gregorian months don’t, so what even is the point of having them.

    • how long the moon takes to orbit the Earth (29.5-ish days) has nothing to do with how long the Earth takes to orbit the sun, so they’ll never fit neatly into each other. unlike days and years, moon phases don’t even affect our lives, so they shouldn’t be a key component of the calendar. they should just be tidbits for those who care.

  • the first day of the year is some arbitrary day in the Earth’s orbit, when it should obviously be the first day of a season.

if we were to design a new calendar from scratch, we would actually base it on the Earth’s year.

the Earth’s year

the key segments of the Earth’s year are its seasons. the seasons are caused by the Earth’s tilted spin as it orbits the sun, divided by 4 key moments in the year.

  • when the axis of the Earth’s spin tips closest to the sun, that’s the longest day of the year and the first day of summer: the June solstice (in the northern hemisphere).

  • the opposite is the first day of winter: the December solstice.

  • in between are the first days of spring and fall, where day and night are the same length, and the axis doesn’t tilt toward or away from the sun: the March and September equinoxes.

these 4 sections of the year should be the main focus of any Earth calendar.

my calendar

(at first), i made the first day of my calendar the first day of spring. this would give us a nice yearly cycle where things grow at the beginning of the year, peak somewhere in the middle, and get cold and die at the end. (sorry southern hemisphere, but 90% of humans live in the north half.)

then i divided the year into quarters for the seasons. 365 days divides into 4 × 91 days per season, plus 1 day extra, which i called “Remainder Day” and declared the 92nd day of winter.

for leap years, i put Leap Day after Remainder Day, so winter would have 93 days compared to 91 for the other seasons.

the year always starts on a Monday. Remainder Day and Leap Day are technically Monday and Tuesday, so when the calendar restarts we would get an awkward Monday-Monday or Monday-Tuesday-Monday, but everyone would probably just take Remainder Day and Leap Day as holidays anyway.

3 - calendar, initial version

you’ll notice i kept 7-day weeks. there’s no reason why this is the best week length; it’s just arbitrary. the only reason i used 7 is because 7 × 13 is the only factor pair for 91. if the Earth’s seasons had happened to be 90 days long, for example, i might have divided them into fifteen 6-day weeks, but that still would have been arbitrary.

the only reason to even have weeks at all is because humans find it useful to have a short cycle a few days long. but nothing about human physiology or the Earth’s year makes, say, 6 better than 7, or 7 better than 8; any choice of week length would still be arbitrary. the point being, don’t interpret my use of 7-day weeks to mean that 7-day weeks makes sense. it’s just a lucky coincidence.

today’s date is notated as y12,019 s1 d44, which means “year 12,019, season 1, day 44” (based on a better year 1 for humanity). that means we’re almost halfway through winter, and almost 1/8 of the way through the entire year.


the day-of-the-week problem goes away. for every season of every year, days 7, 14, 21, and so on are all Sundays. days 8, 15, and 22, which multiples of 7 plus 1, are all Mondays, and so on.

more importantly, this calendar focuses our attention on the seasonal cycle, keeping us in better touch with the Earth. Earthlings matching their lives to the Earth makes so much sense that it’s almost spiritual—and i say that as a non-spiritual person.

i find this system incredibly elegant. it’s completely based on the Earth’s year, with as few arbitrary decisions as possible. if you went to Mars, you could make a Mars calendar based on the exact same principles, just with a different number of days in the year.

now presenting a similar calendar

what would you name my calendar? ideally, the name would be self-defining, so clear that you would know how it worked just by reading the name. got any ideas?

the answer: Seasonal Calendar.

since this system is so logical and minimal, i figured other people had thought of it before. whenever possible, it’s best to not make a new standard, but try to work with existing standards. i was also curious if i had missed any good ideas in making my own system.

so i encountered Calendar Wiki’s shitload of alternative calendars, and i searched for “season” at first, but i also skimmed every single page to see which were season-based. (i immediately rejected any calendar with months.)

the simplest and most elegant one was the World Season Calendar, created by… Isaac Asimov, for his book The Tragedy of the Moon. so apparently we think alike.

differences between our calendars

first day of the year

the first day of Asimov’s calendar was the winter solstice, instead of the spring equinox. why?

when i was checking my math on solstice and equinox dates, i was confused to find that the seasons aren’t exactly 91 days each: spring has 93 days this year, for example. then i remembered it’s because the Earth’s orbit is an ellipse, not a perfect circle. the seasons won’t fall exactly on all 4 calendar quarters—they’ll always drift by a few days.

this presents a decision: which season should we synchronize the calendar to? any of the 4 would work, but only the chosen one would be guaranteed to start on the same date every year. a solstice actually makes a little more sense, because it’s an extreme of day length, rather than a midpoint between extremes. it’s conceptually simpler; if the entire world hypothetically lost track of the date, it would be easier to reacquire the solstices than the equinoxes.

leap day

Asimov put the leap day in the middle of the year, after the second season, rather than at the end of the year. this makes sense because in leap years, this would space out Leap Day and Remainder Day (which Asimov called “Year Day”) to make the solstices and equinoxes occur closer to the quarter boundaries. clever.

my calendar, updated

4 - Seasonal Calendar

in the end, i changed these mechanics of my calendar to match Asimov’s, and yes, this is how my goddamn planner is numbered. i have the 1sts of the Gregorian months written in for quick reference, although if you know how to calculate day numbers and add or subtract 11 (the difference between the winter solstice and Jan 1st, which varies in some years), converting between the calendars is actually pretty easy.

last of all, the truly best name for this calendar isn’t actually Seasonal Calendar, but Earth Seasonal Calendar. that would open the door for Mars Seasonal Calendar and so on. should we someday inhabit, say, Titan or Europa, which are moons, we’d have to add to the system because moons have more complicated timing cycles than planets. i’ll have to think about that sometime.