2026-10-26

Planetary orbital period multiples that align to Earth years

Assuming that one Earth orbit takes $365.242199$ days, the following table notes the durations at which the other planetary orbital periods come close to a multiple of Earth's. The associated error, as a percentage of the planet's orbital period, is noted as well.

Planet Orbital Period Multiple Number of days Earth years Error (day) Error (%)
Mercury 87.9691 328 28,853.8648 79 0.268921 0.306
Mercury 87.9691 191 16,802.0981 46 0.956946 1.088
Venus 224.701 13 2,921.113 8 0.824592 0.367
Mars 686.98 42 28,853.16 79 0.973721 0.142
Mars 686.98 25 17,174.50 47 8.116647 1.181
Mars 686.98 17 11,678.66 32 9.090368 1.323
Mars 686.98 8 5,495.84 15 17.207015 2.505
Jupiter 4,332.59 29 125,645.11 344 1.793544 0.041
Jupiter 4,332.59 22 95,316.98 261 11.233939 0.259
Jupiter 4,332.59 7 30,328.13 83 13.027483 0.301
Saturn 10,755.70 29 311,915.3 854 1.537946 0.014
Saturn 10,755.70 9 96,801.3 265 12.117265 0.113
Saturn 10,755.70 2 21,511.4 59 37.889741 0.352

This is closely related to how long a planetary "analemma" takes to form an approximately closed curve. The "Error (%)" column indicates how close it comes to making a true closed curve. This assumes that the orbital elements of the planet are constant over the period in question which we all know is not true.

The above numbers were what I relied on when tracing the analemma curves in previous blog posts. For instance, I chose the $59$ year interval for Saturn (here) as other options ($265$ or $854$ years) were too long. My choice of $12$ years for Jupiter (here) was an early approximation, and I need to regenerate the trace again over an $83$ year interval instead.

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