If humans colonised Mars, how would they calculate time, as a Martian day is longer than one on Earth?
Bob McCrossin
Cooroy, Queensland, Australia
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It is more complicated than you might think, if you don鈥檛 have a clock.
There are three kinds of day to consider. The sidereal day is the planet鈥檚 rotation period to come back to the same position compared to the fixed stars. The solar day is the period for the sun to come back to the same spot in the sky. It is a bit longer than the sidereal day because the planet has advanced in its orbit around the sun and the elliptical orbit makes the 鈥渟ame spot鈥� not quite so.
The astronomical times to the nearest minute are: Earth sidereal 23 hours 56 minutes, solar 24h; Mars sidereal 24h 37m, solar 24h 40m.
Finally the human diurnal (daily) rhythm is the time the body 鈥渢hinks鈥� it has done a day鈥檚 worth of metabolising and restarts. The body adjusts to the solar day by referencing the sun. Humans with no light perception have an , so we are actually slightly better adapted to Mars.
The Martian hour would need adjusting, but an alternative would be to retain Earth hours and follow the Roman tradition of the Saturnalia used to line up the lunar and solar years. This would mean 40 minutes of party time at the end of each Martian day.
There is, of course, a theory we actually came from Mars, or at least that is where early microbial life may have come from. But who knows? Maybe we originated on the planet Golgafrincham.
Alex McDowell
London, UK
In the books Martian Time-Slip (1964) by Philip K. Dick and Mars Trilogy (1992-96) by Kim Stanley Robinson, Mars settlers use clocks like those on Earth, except that, at midnight, the clocks stop for 39 minutes and 35 seconds (the extra length of a Martian solar day) and then start again.
Since the Viking craft reached the planet in 1976, Mars landers have used clocks that divide a Mars day, or sol, into 24 鈥淢artian hours鈥�. Planetary scientists define the Martian new year as starting on its vernal equinox and have defined a Mars calendar.
Mars colonists may be more radical and use a Martian decimal time system, in other words, divide the Martian day into 10 hours and the hours into 100 minutes.
Stephen Johnson
Eugene, Oregon, US
Time, be it on Mars or Earth, is a human construct used to help us organise and regulate many aspects of life.
Originally, humans divided the day into two parts, day and night. Later, with the invention of sundials and primitive clocks, we started to divide the day into smaller units. The 24-hour day came from the Egyptians along with the sexagesimal number system they used, with a base of 60. This system, previously used by the Babylonians, divided both the circle and the year into 360 segments. Our use of 24 hours, 60 minutes in an hour and 60 seconds in a minute all come to us from this system.
The important point is that time wasn鈥檛 a fixed interval, but an arbitrary one based on dividing the day into 24 parts. On Mars, the easiest way to tell time is to use the exact system of hours, minutes and seconds that we use on Earth, but to make each second 2.75 per cent longer to account for the extra time in a Martian day. This is the convention all craft that landed there to date have used. No doubt for some science on Mars, a form of radioactive decay, or crystal vibration frequency, will be used to ensure identical intervals to those used on Earth when making measurements.
Pat French
Telford, Shropshire, UK
The New Martians will quickly establish their own routines. The difference in day length compared with Earth is only about 40 minutes. They could choose any subdivision of a Martian day that they liked to replace hours.
The Martian year is almost twice as long as Earth鈥檚 and a Mars calendar is likely be independent. A phone application could simply convert months to Phobosths (Phobos moon cycles) in much the same way that today鈥檚 conversion tables convert kilometres to miles and vice versa. Birthdays will be a long way apart on Mars, 687 Earth days to be precise.
There are some very precise chronometers involved in satellite navigation and in the calculation of flight paths, trajectories and orbiting speeds. This requires calculations involving the speed of light. For these purposes, there needs to be a precise standard time system. It is probable that the current system will continue to be used, at least until the time of Martian independence comes.
Rob Walker
via Facebook
We would divide the 24.6 hours of a Mars day into three equal bits. One for work, the second for rest and, finally, a period of play. Because, as we all know, a Mars day helps you work, rest and play!
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