Reply To: Jupiter’s closest opposition since 1963

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Steve Holmes

I also analysed this situation in some detail, having seen many reports on the Internet about “nearest for 59 years”, with some claimimng 70 years. I came to the same general conclusions as Dominic and John – that this year’s opposition was closer than those dating back to 1963 / 1951 because although the perihelion to opposition interval was slightly greater than average (when the average is taken over the most recent cycle) and perihelion itself was very close to average, the combination of the two parameters was the most favourable overall during this period. This is because of the phase difference between the ~83yr cycle of perihelion-opposition intervals and the 59-yr cycle of closer perihelions.

During the period prior to the present, perihelion distances were smaller than average for the 2010 and 1999 oppositions but the perihelion-opposition intervals were greater, and then although the p-o interval in 1987 and 1975 was less than average the perihelion distance was greater. It was not until 1963 that near optimum conditions were reached again, with a minimum p-o interval and just above average perihelion distance. The situation in 1951 was then even better, with a much less than average p-o interval but a minimum perihelion distance. Things got steadily worse before that, with both the p-o interval and the perihelion distance steadily increasing.

However, it should be noted that the variation in Sun-Earth distance has a greater effect on the results over this period than might have been assumed from Dominic’s final paragraph. While it is of course true that the variation in Jupiter’s orbit is greater than that in the Earth’s, it is important to consider distances at opposition rather than at Jupiter’s perihelion, and because of the large changes in perihelion-opposition interval the opposition distances have a different “variation profile” from the perihelion distances alone. In fact, the Sun-Earth distance at opposition in 2022 was from 0.0077 to 0.0021AU greater than in all the oppositions from 1999 to 1951 while the Sun-Jupiter opposition distance varied from 0.0027AU greater to 0.0058AU smaller than 2022 over the same period. It can thus be seen that the two variations in distance actually had the same degree of influence on the final result.

A very interesting analysis to undertake, however!