The current sentence attributes stellar parallax reasoning to Aristarchus, but ancient astronomers viewed the fixed stars as lying on a single celestial sphere at the same distance. Stellar parallax, meaning a shift of nearby stars relative to more distant ones, only applies in a three-dimensional universe with stars at different distances, a concept that developed much later.
The actual ancient concern was that if Earth’s orbit were large compared to the stellar sphere, the apparent angular separations between stars would change over the year, altering the shapes of constellations. Since constellations appear constant, the stellar sphere must be extremely distant.
I therefore propose replacing the sentence with a historically accurate alternative:
“Aristarchus presumably took the stars to be very far away since if Earth’s orbit were significant relative to the size of the celestial sphere the apparent sizes of the constellations would vary over the course of the year.”
Instead of the previous sentence:
“Aristarchus presumably took the stars to be very far away because he was aware that their parallax would otherwise be observed over the course of a year.” KADEG17 (talk) 01:59, 8 December 2025 (UTC)
- I agree that as far as is known he would have been considering how a change in viewpoint would change the apparent positions of points on the inside of a celestial sphere, rather than how a change in viewpoint would change the view of a vast three-dimensional set of stars. I do have to disagree with you to the extent that an observation of differences in the appearance of the inside of a sphere depending on the observer's viewpoint would be an observation of parallax, if of a different sort, so the old wording was technically correct. Still, we don't need to get into the minutia of how parallax works here and your wording seems like an improvement to me. --Noren (talk) 19:00, 8 December 2025 (UTC)
- As I've commented on the talk page for Aristarchus of Samos: I disagree that calling the concept parallax is anachronistic, since it's an accurate description of the observations being made, even if the concept of stellar parallax was not formalized until later.
- Adding here: This is supported by the fact that the sources also use the term parallax to describe his observations (e.g., ). MossOnALogTalk 21:51, 9 December 2025 (UTC)
- I have commented on the talk page for Aristarchus of Samos where I attempt to clear my reasoning up, thanks for the feedback KADEG17 (talk) 23:02, 9 December 2025 (UTC)
- Your argument makes sense, reverting my revert. MossOnALogTalk 18:59, 10 December 2025 (UTC)
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