Timeline of astronomy Rectification of Planetary Theory", eliminated the need for an equant by introducing an extra epicycle, departing from the Ptolemaic system in a way very similar to what Copernicus later also did. Ibn al-Shatir proposed a system that was only approximately geocentric, rather than exactly so, having demonstrated trigonometrically that the Earth was not the exact center of the universe. His rectification is later used in the Copernican model. Nicolaus Copernicus publishes "De revolutionibus orbium coelestium" containing his theory that Earth travels around the Sun. However, he complicates his theory by retaining Plato's perfect circular orbits of the planets. A brilliant
Theory of the Earth evidence of the past action of processes which still operate today. He also anticipated natural selection, as follows: Hutton's prose hindered his theories. John Playfair in 1802 restated of Huttton's geological ideas in clearer English. However, he left out Hutton's thoughts on evolution. Charles Lyell in the 1830s popularised the idea of an infinitely repeating cycle (of the erosion of rocks and the building up of sediment). Lyell believed in gradual change, and thought even Hutton gave too much credit to catastrophic changes. Hutton's work was published in different forms and stages: Theory of the Earth Theory of the Earth