How Long is a Year on Mars?

by Jerry Coffey on June 3, 2008

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So, you were sitting there wondering how long is a year on Mars? It lasts 686.98 Earth days or 1.88 Earth years. Now, given that a day(sol) on Mars is longer than on Earth, you would get a different answer. If you were standing on Mars, a year would take 668.5921 sols. In other words, Mars rotates 668.5921 during one orbit about the Sun.

Another question that commonly comes to mind about the Martian year is whether or not the planet experiences seasons. Mars has an axial tilt of 25.192 degrees. Since seasons are fairly dependent on axial tilt, you can see that the planet does have seasons. Here on Earth, where we have a less elliptical orbit than Mars, the seasons are of about the same length. Mars; however, has a more eccentric (0.0934) path around the Sun. Kepler’s laws of orbital motion, tell us that Mars travels more slowly in its orbit when it is further from the Sun, and more quickly when nearer. Mars reaches aphelion(its furthest point from the sun) during spring in its northern hemisphere. This makes spring the longest season. The seasons would last about this long: Spring…7 months, Summer…6 months, Fall…5.3 months, and Winter…just over 4 months.

Given the differences in seasons and day length, could a standard Martian calender be developed? Yes, but it would face many problems. Calendars must take into account the astronomical cycles of a planet: its day and its year. Calendars must also serve to mark human cycles that are unrelated to astronomical cycles, like the seven-day week. Another consideration in designing a calendar is accounting for the fractional number of days in a year. Earth’s year is 365.24219 days long, and so calendar years contain either 365 or 366 days accordingly. Such a formula would need to be developed to account for the 668.5921-sol Martian year. All of that may make you wonder why a Martian calender would ever be necessary. There is an earnest push to put man on Mars. The trip is too long to just stop by for a few days like we did on the Moon. Additionally, if man were to ever put a space station on, or in orbit above, the planet a standard Mars calender would need to be developed.

”How long is a year on Mars?” is like so many astronomy related questions, it leads to at least a dozen others. Hopefully, you have found what you need and the inspiration to look for more.

NASA’s Mars rovers have been working so long, they were hired on for a third year. Here’s an example of when Mars is at its closest approach.

All you ever wanted to know about Martian time. Information from NASA about Spirit celebrating 1 year on Mars.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Source: NASA

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