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 Book of the Short Sun least "Locus: The Magazine of the Science Fiction & Fantasy Field" considered the three "Short Sun" volumes separately for annual "Best Novel" awards. The "Short Sun" of the title is an ordinary star, in contrast to the "Long Sun" of the Whorl where the narrator grew up. Most of the story takes place in a star system with two habitable planets, Blue and Green, which lend their names to the first two volumes. The Whorl of volume three's title is the generation ship setting of "Long Sun". The Tor hardcover editions (see table) were almost 1200 pages long in sum.