How long is a Mars day?
The unit of a calendar is a day. A day should be relatively easy to define since the concept is already established by observation. One easy definition is the time span from one physical event, such as solar zenith (noon), to the next occurence of that event. In that the physical events occur at different absolute intervals, this day has varying lengths. Another definition would be a fixed number of seconds that approximates a ficticious mean of the span between solar zeniths. This second definition would be fixed to the accuracy of a second. This second definition could be adjusted periodically with leap seconds to maintain the yearly relation to the true varying day. A Julian Day is 86400 seconds of International Atomic Time. This definition of a day follows after the second definition of a day for Earth. How accurate is it? Leap Seconds are added about every year to adjust the time system to the observed rotation of the Earth. Based on the Modified Tropical Year, the number of times
