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
The Dark Side of the Sun of CY Aquarii) settled by a joint party of phnobes and earth-humans. The planet is mostly water and marsh. Their wealth derives from both the chance discovery of "pilac", a safe death-immunity drug and "googoo", a fungal copier and regenerator of human tissue. The vegetation is blue. 52 different sentient species (including earth-humanity) exist in the novel. Chief among them are: The rest: The Dark Side of the Sun The Dark Side of the Sun is a science fiction novel by Terry Pratchett, first published in 1976. It is similar to the work of Isaac Asimov. According to Don D'Ammassa,