Every decent world building exercise requires a history and a calendar. Sublight's Universe takes place in an alternate history to ours, that split off on September 11, 1777. In our world, Ferguson decides not to shoot George Washington. In their world, he did.

I tried to pick a date close enough in history that we would have a lot of literature and culture in common. But far enough away that I can reimagine events like the Industrial Revolution and the First World War.

Their culture has a lot more Eastern influences, and as a result of Japan being involved in a lot of early standards, space societies in the Sublight Universe to not recognize the Gregorian Calendar. They also find Japan's system of "the Year of the Emperor" to be a bit limiting, so in the late 19th and Early 20th century, the world created the metric calendar.

Metric calendars tries to preserve the spirit and rhythms of an Earth year, while recognizing that Earth's cycles are to imperfect for decent record keeping. Absolute time is kept in an adapted form of Julian Days.

As the standards board was meeting in the late 19th century, they would probably look for the nearest roll-over to the next digit as the star of the modern era. That would be Julian Day 2400000 (Tue Nov 16, 1858). This blog entry was made on 2021-02-27, which would be star date 59273. If you have a handy Tcl interpreter, you can calculate star dates with the clock command:

clock format [clock scan $date] -format %J

In Excel, you can use the built in date functions. Excel uses a serial date system. Day 1 is the January 1, 1900. To convert between Sublight stardates and Excel serial dates, Subtract 15018.50. (Julian dates are noon to noon.)

And just remove the leading 24. This number system will work well until Julian Day 2500000 (Sun Aug 31, 2132). Which, oddly enough, will happen towards the end of Book 2. That gives me a nice lead up to something akin to the y2k crises.

For day to day scheduling, serial dates aren't too useful. Space settlements utilize a 364 day calendar. 364 is 52 time 7. The year is broken into 4 quarters, with 3 28 day months, and one 7 day "Holiday."

Metric calendar year 1 starts on Gregorian calculator date 1859-12-20, Julian day 2400034. This was the Monday before the winter solstice after the start of the epoch in 2400000. To figure out what "year" you are in, add 34 and divide your Star date by 364. My handy chart includes what day of the year is.

Today on the Gregorian calendar (2021-02-27). This is star date 59273.

 59273+34 = 59307
 59307 / 364 = 162
 (59307 % 364)+1 = 340

This would be Metric year 162, day 340. Which would be December 11. Which sounds wonky, but over 162 years the Metric calendar lost 201.2 days. (Tropical years are 365.242189 days plus or minus 15 minutes).

This sounds like a huge discrepancy, but remember in the 1800s the world was still transitioning from the Julian calendar to the Gregorian calendar. People were grappling with different calendar systems that were off by months as well. Legend has it that the Russians showed up a month late to the first Olympics because they were still on the Julian Calendar. And they are both Christian cultures. And then you have lunar calendars in Islam and Judaic cultures. And then there's the Chinese calendar.

So a Metric calendar that makes calendar calculations easy, and can be adapted for space. You can't slave your standards to Earth's orbit. Earth's orbit wobbles, drifts. The planet's rotation is also slowing. So a ratio of how many days is a year is meaningless in the long term. Since Julian day 0 (around 4713 BC), the Earth's day has gotten upwards of 10 seconds longer.

So... in the end, yes. The new calendar is a little weird. But, then again, so were all of the calendars that preceded it. As it is, we still have to consult an astronomer to figure out when the Solstices and the Equinoxes will actually be.

NOTE: This calendar has been superseded by the one developed in: Revised Metric Time Calendar