Orrery on display in Kassel at the Astronomisch-Physikalisches Kabinett and in Dresden at the Mathematisch-Physikalischer Salon. In "De revolutionibus orbium coelestium", published in Nuremberg in 1543, Nicolaus Copernicus challenged the Western teaching of a geocentric universe in which the Sun revolved daily around the Earth. He observed that some Greek philosophers had proposed a heliocentric universe. This simplified the apparent epicyclic motions of the planets, making it feasible to represent the planets' paths as simple circles. This could be modelled by the use of gears. Tycho Brahe's improved instruments made precise observations of the skies (1576–1601), and from these Johannes Kepler
The Sun Saboteurs Earth Quarter"; and in the UK under the original title in the omnibus "Two Novels". In the future, Earth has been devastated by war and disease and supports only a primitive agrarian society. Most Earthmen live elsewhere, as émigrés on planets that are populated by alien species. The author suggests that the human species is the only one plagued by "original sin", i.e. by an innate tendency to lie, cheat, kill; aliens have come to accept these traits without understanding them. The story takes place among a group of humans in the "Earth Quarter", a ghetto on the planet Palu