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
Planets of the Hainish Cycle current estimate. On the other hand, giant stars last 100 million years or so, which is much less time than Earth needed to evolve complex life. It is probable that the native humanoids are of Hainish origin, as are many other indigenous populations in the Hainish Cycle, descendents of genetically modified Hanish colonists from the ancient Hanish colonial epoch, similar to other planets in the cycle. This would account for the successful imbreeding, which should not be possible if they had evolved from completely different biospheres. In 1.5 million years, Eltanin will pass within 28 light years of Earth. At