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 Continent Makers and Other Tales of the Viagens mid-21st-century to the mid-twenty-second. Individual stories are set on spaceships traveling between planets and individual planets such as Earth, Krishna, Ganesha and Osiris (it being assumed that Terrans will have carried their penchant for naming planets after gods to other star systems). Features of the postulated future include an Earth governed by a World Federation in which Brazil has become the paramount great power, with Terran space travel monopolized by a Brazilian-dominated agency called the "Viagens Interplanetarias" ("Interplanetary Tours" in Portuguese). Interstellar travel is limited to sub-light speeds, as the author eschews such common science fiction gimmicks as hyperdrives. The