Geocentric model the coordinate system in order to predict the motions of planetary bodies, though doing so may make calculations easier to perform or interpret. A geocentric coordinate system can be more convenient when dealing only with bodies mostly influenced by the gravity of the Earth (such as artificial satellites and the Moon), or when calculating what the sky will look like when viewed from Earth (as opposed to an imaginary observer looking down on the entire solar system, where a different coordinate system might be more convenient). The Ptolemaic model of the solar system held sway into the early modern age;
Central Europe do not clearly define the region, but Encarta places the same countries into Central Europe in its individual articles on countries, adding Slovenia in "south central Europe". The German Encyclopaedia "Meyers Grosses Taschenlexikon" ("Meyers Big Pocket Encyclopedia"), 1999, defines Central Europe as the central part of Europe with no precise borders to the East and West. The term is mostly used to denominate the territory between the Schelde to Vistula and from the Danube to the Moravian Gate. Usually the countries considered to be Central European are Austria, Croatia, the Czech Republic, Germany, Hungary, Poland, Slovakia, Slovenia, Switzerland; in the