The conventions that
we use to track the passage of time in a day, week,
month, or year are clocks and calendars. People rely
heavily on the clock in order to schedule their tasks,
and on the calendar to plan their weekly work, meals,
and exercise and recreation times. Months help people
understand the passage of longer periods of time and
tell us what season it is.
For future Martian explorers
and settlers, a year will mean something different
than a year does to us on Earth. How explorers
keep time on the planet Mars will be an important
factor in structuring days, work assignments,
free time, and communication with Earth.
here to read about how humans have organized their
lives with calendars throughout history.
How long is a day on Mars?
The rotational period of Mars is officially 24.6229 hours or 24 hours,
37 minutes long. You might have read somewhere that the Earth’s rotational
period is actually 23 hours 56 minutes long. So where are the other
four minutes each day?
The difference is that the 23 hours 56 minutes number is a sidereal
day; that is, the Earth's rotation measured from the point of
view of a fixed reference angle in space. Here is a nice
little animation to explain it to you.
But as Earth turns once on its axis, it also moves along its orbit
around the Sun, and so the direction from the Earth to the Sun
changes slightly. It takes Earth an extra four minutes to rotate through
this additional angle, and so Earth’s solar day, measured from the
point of view of the Sun, is 24 hours. (Remember that the breaking
up of the Earth day into 24 segments called hours is a human convention,
unrelated to astronomical cycles.)
This same principle applies to Mars. Although the sidereal
day is 24 hours, 37 minutes, the solar day (known as sol)
is 24 hours, 39 minutes, 35.2 seconds.
here to read about Martian Standard Time.
Time, Continued (pg. 15 of 35)