De revolutionibus orbium coelestium Earth's axis rigidly to a Sun-centered sphere. The unfortunate consequence was that the terrestrial rotation axis then maintained the same inclination with respect to the Sun as the sphere turned, eliminating the seasons." To explain the seasons, he had to propose a third motion, "an annual contrary conical sweep of the terrestrial axis". It was not until the Great Comet of 1577, which moved as if there were no spheres to crash through, that the idea was challenged. In 1609, Kepler fixed Copernicus' theory by stating that the planets orbit the sun not in circles, but ellipses. Only after Kepler's
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,