Crowdsourcing dynamic illustrations for a new astronomy book(observablehq.com)
observablehq.com
Crowdsourcing dynamic illustrations for a new astronomy book
https://observablehq.com/@jsomers/we-need-more-tiny-knowledge-projects-heres-one
https://observablehq.com/@jsomers/we-need-more-tiny-knowledge-projects-heres-one
https://en.wikipedia.org/wiki/Great_conjunction#/media/File:...
This is the so-called "trigon" which was used to predict the location of Great Conjunctions over time. Each conjunction between Jupiter and Saturn occurs every 20 years and about 120 degrees separated in the sky, thereby forming a triangle. But after a cycle the triangle gets rotated by about 8 degrees, so over time you see a slowly rotating triangle. After three or four cycles the locations of the conjunctions shift from one set of constellations to another. These shifts were considered astrologically significant and received a lot of study.
At any rate, this drawing inspired Kepler to try using inscribed polygons to model the distances to the planets. This did not fit the data well so he generalized to three dimensions with Platonic solids and ended up with the model represented by the figure in the article.
It is a shame that it is so difficult to produce good, clear illustrations because, as the article explains, a clear diagram can make a tremendous difference in understanding a difficult concept.