You may think it’s a few weeks early to celebrate the New Year, but that’s only because you’re an Earthling: November 12, 2024 marks the new year for Marswhen the calendar turns page 37 to 38.
And here I am, still putting 37 on all my checks.
Why would anyone choose November 12 as New Year’s Day for Mars? And why does our official Mars time calculation set the Red Planet as only 38 years old? The answer involves a combination of natural cycles and the human need to establish order through somewhat arbitrary timing, just like on Earth.
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Here on our home planet, most countries use it gregorian calendar to keep track of the year. It was first adopted in 1582 (although it took quite a while to spread around the world) and is your standard 12-month calendar: 365 days each year, with an extra day added every four years (a “leap year”). The Gregorian calendar begins on January 1 as a legacy of its predecessor, the Julian calendar of the Roman Empire; To honor the god JanusJulius Caesar declared that day the first of the year.
As an astronomer, I would like to mark the first day of the year using a date of astronomical significance. The problem is that the Earth stubbornly refuses to play nice with any set calendar. For example, our planet’s path around the sun is an ellipse, or an oval shape. This means that there is a moment when it is closest to the sun, which we call it perihelion. It seems like a natural date to start a new year.
But Earth’s orbital shape changes subtly each year due to the gravitational influence of other planets, changing the exact time of perihelion. Another adjustment to perihelion time comes from Earth’s moon, which pulls our planet to wobble a bit as we orbit the sun. This is an impossible way to start a perihelion calendar, even though perihelion also occurs in January. (Aphelion—when the Earth is furthest from the sun—occurs in July.)
If you know a little more about astronomy, you can try tagging the new year with equinoxes or solstices. These dates are based on Earth’s axial tilt, our planet’s approximately 23 degrees to the plane of its orbit. (that’s why you always see the balloons in the room bent on their stand). The June solstice, for example, occurs when the planet’s north pole is most inclined toward the sun, which occurs on the 21st of each year. (Note that this occurs during the winter for people in the Southern Hemisphere, which is why astronomers tend to refrain from calling it the “summer solstice”).
Astronomers prefer to measure everything in the sky relative to the March equinox, also called the vernal equinox (“of spring”), as a remnant of Northern Hemisphere-based timekeeping. There are many ways to think about the March equinoxbut astronomers believe that the sun’s position in the sky is the moment it crosses the celestial equator, the projection of the Earth’s equator in the sky. This is useful in time and space for measuring things like the positions of planets and stars.
But again, since the shape of the Earth’s orbit is changing, using it to mark the new year would be a problem. The calendar date changes every year, adding heavy layers of chronological complexity.
So what does all this have to do with Mars?
At the beginning of the 20th century, when humans began to study Mars with more powerful telescopes, we saw global changes across the planet in sync with its changing position in its orbit. Then, with the excellent in situ observations from our probes sent to the Red Planet, it became clear that we needed some sort of Martian calendar.
Such a calendar would have to be very different from ours. The most obvious reason is that Mars is farther from the sun and takes almost two years to complete one orbit around our star; A Martian year is about 687 Earth days!
A day on Mars –called solTo distinguish it from an Earth day—it’s also slightly longer than ours, lasting 24 hours, 39 minutes, and 35 seconds. There are about 668 sols in a Martian year.
But these differences are truly liberating because they free us from the historical legacy of an arbitrary socio-political machine. On March, we were able to start over, determining when we wanted to start the year essentially from scratch.
So the planet’s scientists decided to start the Martian new year at the time of the planet’s spring equinox. Like Earth, Mars’ axis of rotation is tilted relative to its orbit, and Mars has a relatively Earth-like axial tilt of about 25 degrees. This means it has seasons similar to ours, creating global changes previously observed by astronomers. As temperatures rise during the Martian spring, dust storms form, some of which grow so large they can cover much of the planet. The onset of summer in a certain hemisphere warms the corresponding polar ice cap, which shrinks in size during sublimation (it changes from solid to gas).
Why not use the equinox as the starting date then? If we have to choose a date, that makes sense at any age.
If only things were that simple. The earth’s orbit around the sun is very nearly a circle, and the seasons last about three months. But Mars’ orbit around the sun is elliptical. When the planet is closest to the sun (in winter in its northern hemisphere) its orbital speed is faster than when it is farthest away (in northern summer), and combined with its oval orbital shape, this it means that the seasons have significantly different lengths. Northern spring has 194 sol, summer 178, autumn 142 and winter 154 sol.
These strange seasons would make life on Mars strange. I mean, of course it would tough: the thin suffocating atmosphere, high radiation levels, lack of quick and easy access to supplies from Earth, etc. would make life there very difficult. But the rogue schedule would be a constant source of additional irritation.
And about the number of the year: the curious fact that our Martian calendar has so far advanced only 38 years? Scientists decided to mark the year 1 in 1956 when a large dust storm swept across the surface of the planet.—One of the most remarkable events on other planets at the beginning of the space age. The vernal equinox of that Martian year occurred on April 11, 1955, so it is now accepted as the planet’s first New Year’s Day. To make things less ambiguous, scientists also defined the year 0 as starting from the previous equinox, May 24, 1953. This avoids quirks like the Gregorian calendar, which does not have a year 0, which creates strange situations such as new centuries. Starting with years ending in 01 instead of 00. (The 21st century, for example, began on January 1, 2001.)
Put it all together, and you see that Mars’ Year 38 begins on November 12, 2024, on Earth’s Gregorian calendar. Around 16:00 Coordinated Universal Time, or UTC (11 a.m. EST). Get your party hats and champagne ready!
And don’t forget: when the clock goes down to zero, it’s time to sing Ares Lang Syne.
