I'm trying to figure out how to calculate Coordinated Mars Time (MTC). Can it be calculated directly from Earths current time/date, or calculated from the current Mars Sol Date (MSD)?

From this wiki page I can calculate the current Mars Sol Date using:

MSD = (Julian Date using International Atomic Time - 2451549.5 + k)/1.02749125 + 44796.0, where k is a small correction of approximately 0.00014 d (or 12 s)

but how would one calculate Coordinated Mars Time?


2 Answers 2


The fractional part of MTC corresponds to a period of 24 Martian hours.


${HH \over 24} + {MM \over 60 \cdot 24} + {SS \over 60 \cdot 60 \cdot 24} = frac(MSD)$

Conversion in the opposite direction is a little more complicated: If $frac$ is the fractional part of a number, and $floor$ is the integer part (rounding by truncation), then,

$$ F_h = frac(MSD); \\ HH = floor(24 \cdot F_h) \\ F_m = frac(24 \cdot F_h) \\ MM = floor(60 \cdot F_m) \\ SS = 60 \cdot frac(60 \cdot F_m) \\ $$


  1. This is according to the convention o using a 24-hour "Mars clock" on which the hours, minutes and seconds are 2.7% longer than their standard (Earth) durations. That means these aren't SI system seconds - these are arbitrary periods of time corresponding to 1/(24*60*60)th of Sol.
  2. HH and MM are integers. SS are given as a Real, including the fractional part of the "second".

we should really find some better names for these time units


On the page you refer: 


MTC is simply the fractional part of MSD, in hours, minutes and seconds:

MTC = (MSD mod 1) × 24 h 
  • $\begingroup$ Yea I saw that after posting the question. Tested it out and it seems to work. I also found a page that stated to use MTC = (24 * MSD) mod 24 which seems to give the same result. Does anyone know how to calculate the MTC strictly from Earth date and time values? $\endgroup$
    – Orbit
    Dec 15, 2015 at 17:03
  • $\begingroup$ Which data you wish to base to? $\endgroup$ Dec 24, 2015 at 11:04

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