Sciency Words: Yestersol

Sciency Words MATH

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:


In the course of my research, I sometimes stumble upon new words that just make me smile. Sol is the technical term for a Martian day, a period of roughly 24.6 hours. Knowing that, I’m sure you can guess what yestersol means.

The term yestersol was apparently coined during NASA’s Spirit and Opportunity rover missions. Scientists and engineers assigned to those missions had to sync their work schedules to Martian time, screwing up their sleep cycles, eating habits, and no doubt many other aspects of their personal lives. This was necessary because the rovers could only operate during Martian daylight hours.

Additional new terms include “tosol” for today and several versions of tomorrow, such as “nextersol” and “solmorrow.”

In the distant future, Earth time may well be retained as an interplanetary standard, but each colonized world will probably develop its own version of local time, along with playful local terminology like yestersol.

Another timekeeping idea that made me smile appeared in Robert Zubrin’s book The Case for Mars. Zubrin suggests dividing Mars’s 687 day-long (or 669 sol-long) year into twelve months based on the twelve Zodiac constellations. So Martian months may end up having names like Sagittebruary, Leotober, or Cancricember.

These months would be significantly longer than Earth’s, but they could be made to correspond with Martian seasons in a manner similar to Earth’s calendar. Martian colonists may find that convenient. Also, who wouldn’t want their birthday (I mean birthsol) to be something like Sagittebruary the 49th?

When world building in science fiction, it can be tempting to either adhere to the familiar Earth calendar or try to impose some sort of intergalactic standard time on everyone. But it might be more fun (and perhaps more true to life) to think about how different communities spread across space might track time in their own unique ways, using their own colloquialisms like yestersol.


Yestersol from Word Spy.

Martian Language: Where Curiosity Can Take You from A Way with Words.

Workdays Fit for a Martian from the Los Angeles Times.

Long Day at the Office as Scientists Get in Sync with Mars from the Sydney Morning Herald.

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Today’s post is part of Mars month for the 2015 Mission to the Solar System. Click here for more about this series.


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