Timeline by Shelton Aikharaekpen

Aristotle

saik0326 — 2025-09-09 15:47:36 UTC

Aristotle (350 BCE): Proposed a geocentric model where Earth was at the center of the universe. All celestial bodies were embedded in a series of 47 to 55 rotating, transparent, crystalline spheres.

Aristarchus of Samos

saik0326 — 2025-09-09 15:48:58 UTC

Aristarchus of Samos (270 BCE): First person to propose a heliocentric theory, placing the Sun at the center of the universe,but his ideas were not widely accepted at the time, primarily because the lack of observable stellar parallax (the apparent shift of stars due to Earth's orbit) suggested that Earth was stationary.

Claudius Ptolemy

saik0326 — 2025-09-09 15:49:48 UTC

Claudius Ptolemy (150 CE): Refined the geocentric model in his work, the Almagest. The complex Ptolemaic system used a combination of circular paths called epicycles and deferents to explain the observed retrograde motion of planets. This model, while intricate, was highly effective at predicting planetary positions and became the accepted standard for over 1,500 years

Nicolaus Copernicus

saik0326 — 2025-09-09 15:50:33 UTC

Nicolaus Copernicus (1543): Published his heliocentric model in De revolutionibus orbium coelestium ("On the Revolutions of the Heavenly Spheres") just before his death. His model correctly placed the Sun at the center and arranged the planets in the correct order, explaining retrograde motion as a natural consequence of Earth's faster orbit compared to the outer planets. However, Copernicus's model still used circular orbits and was no more accurate than Ptolemy's at the time, leading to slow adoption.

Tycho Brahe

saik0326 — 2025-09-09 15:51:07 UTC

Tycho Brahe (c. 1587): Developed a geo-heliocentric system as a compromise. In his model, the Earth remained stationary at the center with the Sun and Moon orbiting it, while the other planets orbited the Sun. His extensive and accurate naked-eye observations, however, provided the data that his assistant, Johannes Kepler, would later use to validate heliocentrism.

Johannes Kepler

saik0326 — 2025-09-09 15:51:43 UTC

Johannes Kepler (1609–1619): Used Tycho Brahe's data to discover his three laws of planetary motion, which proved that planets move in elliptical, not circular, orbits. This refinement greatly increased the predictive power of the heliocentric model and provided a robust mathematical foundation for it.

Galileo Galilei

saik0326 — 2025-09-09 15:52:48 UTC

Galileo Galilei (1610): Used a telescope to gather observational evidence supporting heliocentrism. His discoveries included:
- Phases of Venus: Demonstrated that Venus cycles through a full set of phases, which could only be explained if it orbited the Sun.
- Moons of Jupiter: Showed that not all celestial bodies orbit Earth, proving that the solar system contains multiple centers of orbit.

Issac Newton

saik0326 — 2025-09-09 15:53:38 UTC

Isaac Newton (1687): Published Philosophiæ Naturalis Principia Mathematica, which provided a theoretical explanation for Kepler's laws through his law of universal gravitation. Newton's work showed that the same force of gravity that causes an apple to fall also governs the motion of the planets, solidifying the heliocentric model on a powerful new foundation of physics.

Stellar parallax

saik0326 — 2025-09-09 15:54:16 UTC

Stellar parallax (1838): Friedrich Bessel's measurement of the parallax of the star 61 Cygni finally provided the direct, empirical evidence of Earth's motion that the ancient Greeks had failed to find.

Foucault's pendulum

saik0326 — 2025-09-09 15:54:46 UTC

Foucault's pendulum (1851): Léon Foucault's experiment provided the first direct, physical evidence of Earth's rotation, further undermining the idea of a stationary Earth.