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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