Claudius Ptolemy

2nd-century CE astronomer and mathematician working in Alexandria whose Almagest systematized geocentric planetary models well enough that they stood, essentially unchallenged in their basic form, for roughly 1,400 years — longer than any other astronomical framework in history. His signature device, the equant — a point, distinct from the orbit's geometric center, about which a planet's angular speed is posited to be exactly uniform even though its distance from that point varies — is what let Ptolemaic astronomy fit observed planetary positions to within a fraction of a degree using only circles.

Matters to this vault as the historical pole a 2026 paper is built to argue with: claim-astronomia-ova-orbit-family-satisfies-keplers-second-law-and-exact-equant constructs an explicit orbit family satisfying both an exact Ptolemaic equant and Kepler's second law simultaneously — something neither astronomer's own model could do — and claim-ptolemy-equant-mars-error-8-arcminutes-tycho-precision-forced-kepler-to-abandon-it records the specific empirical gap (an ~8-arcminute error on Mars) that eventually forced the equant's abandonment.

References

• claim-astronomia-ova-orbit-family-satisfies-keplers-second-law-and-exact-equant
• claim-ptolemy-equant-mars-error-8-arcminutes-tycho-precision-forced-kepler-to-abandon-it