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;
Encyclopedia of the Central Intelligence Agency if he would instead be interested in writing an encyclopedia detailing the history of the CIA. Smith agreed as he felt the CIA was highly relevant to military history. "Encyclopedia of the Central Intelligence Agency" was first published in 2003 by Facts on File. It was released in both hardcover and paperback formats. An eBook edition was published the same year. Additionally an eBook was also published in 2003 in Great Britain. In the "Encyclopedia of the Central Intelligence Agency", Smith discusses and defines key concepts relating to intelligence gathering, including "clandestine mentality", a colloquial term used to characterize what