size, distances and time — computed from rotation, orbit and mass
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
The discs are drawn at one scale. The day, the hour, the year in sols and the distances to the neighbours are computed from rotation, orbit and eccentricity in the JPL data.
Mars turns on its axis in 24 hours 37 minutes, but a day is not a turn: while the planet spins it also moves along its orbit, so the Sun returns to the same place in the sky a little later. That difference is what makes a sol — 24 hours 39 minutes 35 seconds. It is the same rule by which the sidereal day on Earth runs four minutes short of the solar one; put the Earth figures into it and exactly twenty-four hours come out.
Mission time on Mars has been kept since the Viking landings of 1976 on an ordinary 24-hour clock divided into one sol. Every Martian hour is therefore 1 minute 39 seconds longer than an Earth hour, and the shift of anyone working to that clock slides 39 minutes later each day, going right around the Earth clock in about 36 sols.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 14 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
