Happy New Year! If you are a Martian!
When it is Sunday, February 7, 2021 on Earth, it will be January 1, 36 (yes, only 36) on Mars: the first day of a new year.
This seems to be based on science, but it is also somewhat arbitrary. I know it sounds like an oxymoron, but bear with me. That’s funny.
Mars is the fourth planet from the Sun. On average, it orbits about 228 million kilometers, compared to 150 million for Earth. Because of this, it orbits slower and has a longer path to travel, so its year is longer than ours: about 687 days (Earth) compared to 365 and it changes for our planet.
Measuring the length of Mars is very good, but when you do that start that measurement? What day do you choose as Day 1?
In many countries (but by no means at all), New Year’s Day is January 1 and this is quite arbitrary; Julius Caesar chose to honor the god Janus, the god of beginnings, after whom January is named. There is no science behind this, no natural event with which to label this. He could just as easily have chosen the first day of any other month*.
But with Mars we have a chance to do this right, and that’s what scientists have done. They decided to base the Martian calendar year after the tropical year and start it on the northern spring equinox.
The tropical year is the time measured from the spring equinox to the spring equinox. For Earth, these are the 365.24 days you’ve probably used to hearing about (and that’s what the calendar year is based on). For Mars, it is 686.6 days on Earth.
Equinoxes (yes, this is the plural for “equinox”) and solstices are related to the axis of rotation of a planet. The axis of rotation of a planet tends to point in the same direction in space, even if the planet revolves around the Sun. The summer solstice is the day when the pole tilts the most towards the Sun (keep in mind that this happens in June for the northern hemisphere of the Earth and in December for the south). The winter solstice is the day when the axis is furthest from the Sun. The equinoxes are when the pole is directed 90 ° away from the Sun.
The Earth’s axis is inclined about 23 ° from the plane of its orbit. Coincidentally, Mars is tilted by about 25 °. That means it has seasons similar to Earth’s!
This gives us a pleasant encounter for the beginning of the Martian year: the spring equinox of its northern hemisphere. It could have been one of the other three seasonal markers, but astronomers tend to use the spring equinox (from spring) for historical reasons.
The beauty is that the Martian vernal equinox is a physical event that we can measure to determine this date. So, unlike our own calendar, one that could be (and possibly will one day) be used on Mars will have a physical basis for its beginning. Mixed.
Because Mars has a longer year and is not even a multiple of Earth’s year, Martian Year’s Day is always a different calendar day on Earth. In 2021 it will fall on February 7.
As it happens, Mars orbits the Sun on an ellipse that visibly deviates from a circle. This complicates matters a bit. When Mars is at perihelion (the closest point to the Sun in its orbit) it moves a little faster than when it is at aphelion (the farthest point). This means that the seasons are not the same length and have dropped quite a bit. Northern spring occurs when Mars is farthest from the Sun, so it is the longest season (about 199 days on Earth), and northern autumn the shortest (145 days on Earth).
One part: You might think that the beginning of the year when a planet is at perihelion makes sense and that, in a way, it has … but the time and date of perihelion can change. On Earth, the gravity of the other planets pulls the Earth and changes the shape of its orbit, and the Moon exerts a decent force on Earth, oscillating it and changing the exact time of the perihelion every year. It’s usually around January 4th (so close!), But that can change a few days from year to year.
The same goes for the equinox, which comes at a different time each year, so it doesn’t make an excellent anchor for the beginning of the year. Worse, the number of days in a year is not even a multiple, which is why we have leap years and that makes things worse. Finally, pointing to a day and saying “Yes, this one is the beginning of the year “it works the same way and in many ways it is simpler.
So, the length of the year is a scientific one. The number of the year – the year Mars 36, in this case – is a bit arbitrary. Year 1 was chosen to begin on April 11, 1955, based on a paper published in (Earth Year) 2000 on seasonal changes in Martian temperature. As it happens, in 1956 there was a big dust storm, which was strongly studied from Earth, which means that it fell to Mars Year 1. Auspicious and good enough to start a calendar.
Later, Mars Year 0 was set to begin on May 24, 1953 – it was supposed to allow the use of negative years, which is useful for scientists. This means that human Martians will argue sometime in the future about the end of the centuries on Mars, but so be it.
Which reminds me: Martian Day is a little longer than Earth Day, about 39 minutes. We call a Martian day “ground” to distinguish them, and I know a few people who work with rovers on Mars who have a schedule set by messengers when they’re on duty. After a few days I imagine that it can become difficult, wanting to eat breakfast at lunch and so on.
Eventually, humans will live on Mars and will have to deal with conversions in time, day, and even year, talking to people on Earth. Different calendars have been launched (and it’s funny to figure them out), naturally, and one day an official one will have to be chosen. Maybe it should happen soon enough, really.
It will definitely be an interesting soil.
*You might think he chose July 1 because the moon was named after him, but it was named in his honor after he died (it was named Quintilis before then), so you go.