Earth and Mars Orbit

Happy New (Mars and Earth) year!

It’s the year 2023 on Earth (by the Gregorian calendar). And it’s the year 37 on Mars (by a NASA calendar). Earth’s New year will start on the 1st of January, the new Martian year started on the 26th of December.

How is that possible?

A year is simply the time it takes a planet to orbit around the Sun. (Earth takes 365 earth-days, Mars takes 687 earth-days.)

But what year is it? To decide the number on Earth or Mars or any planet, we need to decide when to start counting from. For instance, the number 2023 is the number of years that is believed to have passed in the Christian religion since the birth of Jesus Christ. But we could start counting from any point in history. If we started counting from the Moon landings it would now be year 54. If we started from the first recorded flight ever, it would be year 120. If we started from when we believe the first human city was created, it might be year 6001!

So what point in history do we start to count from for Mars?

NASA chose the “first”Martian year (year 1) to start in the Earth year of 1955 for a few reasons. The 1950s was when the Space Age started (with the launch of the first satellite Sputnik in 1957), so all the launches to Mars that humans will ever do, will occur after our martian year 1. The second reason was a global sandstorm on Mars, in 1956 is was wildly viewed from Earth, so it was decided that the first Martian year should include that event.

The one other question is, at what point in Mars’s orbit would a year start from? (Earth, of course, starts in 1st January). On Mars, this is simply another arbitrary choice. Any point could have been chosen. But because Mars experiences seasons like the Earth, it was decided that the martian year would start when the northern hemisphere of Mars starts it’s Spring.

The exact (Earth, Gregorian) start date for the Martian year was the 11th of April, 1955. As each martian year takes 687 earth-days, the start of the second year corresponds with 26th February, 1957, the start of the third year corresponds with 14th January, 1959 . And onward.

So. From Mars’s point of view the Viking 1 landed on Mars in Martian year 12, the Beagle 2 landing on Mars occurred in the Martian year of 26. This author’s birth year was also in Martian year 12, and as it’s now the martian year 37, that makes me only 25 years old. How old are you?


  • Planetary society’s Mars Calendar:
  • Mars – Earth date conversion:

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