When planetary orbits are ellipses, what does a reported distance in AU for a planet like Saturn represent?
Answer
An average over time
Planetary paths around the Sun are not perfect circles but ellipses, meaning the instantaneous distance between a planet and the Sun is constantly fluctuating—the planet is sometimes closer and sometimes farther away than the mean distance. When astronomers report a distance in Astronomical Units (AU) for a planet like Saturn, this figure reflects the average separation calculated over the entirety of its orbit. This accounting for averages rather than fixed, instantaneous positions is a crucial concept when dealing with the dynamic nature of orbits across all scales of astronomical measurement.
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