A sol is the mean solar day, 24 h 39 m 35 s in the fact-sheet rounding. Rover teams count sols from a landing. Climate papers count seasons by solar longitude, Ls. Ls 0 is the start of northern spring. The length of the year in sols is 669.6 sols. [1] [3]

The clock on this page is the NASA GISS Mars24 recipe, documented from Allison and McEwen 2000 and revised on the GISS page dated 2025-01-07. It is checked, before this site builds, against GISS's own worked example. That example is the anchor. Popular tables that round a landing to Ls 5 or Ls 150 are coarser than this algorithm. [2]

Clock

Type a UTC instant and an east longitude. The results are Ls, the northern season, mean solar time on the prime meridian, local mean solar time, and local true solar time. Local true solar time adds the equation of time, which can be the better part of an hour. Mission clocks are often defined at a planned longitude and then left there, so they are not identical to mean solar time at the spot where the vehicle actually sits.

Class C instrument

Screening sheet. Not for flight, medicine, or operations. The anchor is the NASA GISS worked example, not a mission plan.

Ls and mean solar time follow the Mars24 equations (Allison and McEwen 2000, GISS revision dated 2025-01-07). Mean solar time at a site is the prime-meridian time plus east longitude. GISS writes that offset with west longitude. This form converts.

What the anchor proves

GISS publishes the intermediate values for 2000-01-06 at 00:00:00 UTC. Mean solar time at longitude 0 comes out 23:59:39, and Ls comes out 277.188 degrees. If this page cannot reproduce that line, the form refuses to compute. The build runs the same test in Python. [2]

This clock does not compute a radio delay. A distance you type, divided by the defined speed of light, is on Light time. A close approach is a few minutes, and that figure is not stored as today's value. A research ephemeris is NASA HORIZONS, or NAIF SPICE if you need the geometry in a program.

How to use it with the rest of the sheet

Dust-storm season and polar frost follow Ls, not a calendar month. Read Seasons of Mars for why southern summer is the harsh one, and Atmosphere of Mars for the pressure swing that comes with the frost. Elevation changes that pressure again. The screen is Pressure and the areoid, and it uses 6.36 mbar at the mean radius and 11 km from the same constant file as these plates.

See also

References

  1. NASA Goddard Space Flight Center. Mars Fact Sheet. Sol and year. Updated 19 May 2025. https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
  2. NASA GISS. Mars24 Sunclock, algorithm and worked examples. Page updated 2025-01-07. https://www.giss.nasa.gov/tools/mars24/help/algorithm.html
  3. NASA Science. Mars: Facts. Year length in sols. https://science.nasa.gov/mars/facts/

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