Mars Clocks which use standard Earth seconds  --  2025,AstTI,2,210

The Mars solar day of 88775.244 Earth seconds is slightly longer than the Earth day's 86400 seconds.  Current practice for landed spacecraft is to stretch the standard Earth SI second by 1.0274912517 to fit the Earth's 24h/60m/60s time schema onto the Mars day.  But since the SI second is used in all our science and technology, we premise that the residents of future Mars cities will require the use of Earth seconds in their Mars clock.    

To make a practical Mars clock which uses Earth seconds, we set the Mars clock day duration to 88800 Earth seconds (thus 24.756 seconds longer than the Mars solar day), with a scheduled leap-hour correction per every ~150 days.  This Mars clock day has exactly 37/36 duration of the Earth day, thus enabling clock designs which work for both planets.  These clocks are presented in our paper "Mars Clocks and other novel analog clocks, using Earth standard seconds" by Flesch & Sanders (2025), published by Astronomical Techniques and Instruments (AstTI) as 2025,AstTI,2,210. 

The Mars clock day of 88800 Earth seconds cannot be fitted into our familiar Earth clock design.  To make clocks which work for both Earth and Mars, we need an Earth clock which uses just 36 seconds per minute, for which there will be a Mars equivalent which uses 37 sec/min (we call these "short minutes").  Therefore we re-fit the 86400-sec Earth day into a 24h/100m/36s schema, with the Mars version thus being 24h/100m/37s.  To enable this to work on a tidy analog clock dial ("tidy" = clock hands use the same clock face markings), we introduce a new "Martian" clock hand motion:
 
The Martian Clock is an analog 24-hour clock with a unique "Martian" hand movement which strikes the hour when all 3 hands point to that hour on the dial.  This clock counts hours, hundredths-of-hours, and seconds, thus can be written as hh.hh:ss,  for example, 12.87:08, with the "minute" serving only as an alias for 1/100th hour.  It can be used for both Mars and Earth, see the Earth version keeping your local time here --  the digital display is underneath, and the standard Earth time on its browser tab above. 
 
The Relaxed Martian Clock has a pleasantly sparse dial on which the second hand sweeps a leisurely 74 sec/min for Mars or 72 sec/min for Earth (these called "long minutes"), with 50 minutes per hour; thus the schema is 24h/50m/74s for Mars and 24h/50m/72s for Earth.  See it keeping your local Earth time here.  Also it works for 100 min/hour by simply counting each sweep as 2 "short minutes", as seen here -- it's the same analog clock but the digital display underneath counts short minutes instead of long minutes.

If instead a standard (Earth-like) clock hand motion is desired, no 24-hour analog Mars clock can be tidy, but a 20-hour clock does work as 20h/60m/72s for Earth and 20h/60m/74s for Mars.  It features the familiar 60 min/hour plus "long minutes", see it keeping your local time here -- or its 10-hour AM-PM variant here.  The 20-hour display can be confusing at first, so note the standard Earth time on its browser tab above.    


Get the in-depth presentation in our preprint paper here or on arXiv , or the published paper on AstTI at https://doi.org/10.61977/ati2025013  (2025,AstTI,2,210).


Martian Clocks running on your computer desktop:  A zip file (Martian-Clock.zip, v0.2, 2025) provides desktop display of these Mars clocks.  It is initially set to display Earth local time, with 36 seconds per sweep of the second hand, and a digital display underneath it. Other clock hand motions and dials are available, including whether the clock is to be for local time, Earth UT time, or Mars AMT time, or large or small displays; 42 preset presentations are available, and many more options for those wishing to manually tweak the “settings” file.  A Java 7 (or better) run time environment is needed to run this clock.  Get the zip file here -- to be unzipped into any new directory/folder; it includes a ReadMe which details how to use the "settings" file and other manual options.


 Martian Clock hand movement ©2019 Eric Flesch.  

 

Eric Flesch, last updated 15 July 2025