History of astronomy and Definition of planet

The idea of planets has evolved over its history, from the divine wandering stars of antiquity to the earthly objects of the scientific age. The concept has expanded to include worlds not only in the Solar System, but in hundreds of other extrasolar systems. The ambiguities inherent in

Printed rendition of a geocentric cosmological model from Cosmographia, Antwerp, 1539

defining planets have led to much scientific controversy.

In ancient times, astronomers noted how certain lights moved across the sky in relation to the other stars. Ancient Greeks called these lights "πλάνητες ἀστέρες" (planetes asteres: wandering stars) or simply "πλανήτοι" (planētoi: wanderers),^[5] from which today's word "planet" was derived.^[6][7] In ancient Greece, China, Babylon and indeed all pre-modern civilisations,^[8][9] it was almost universally believed that Earth was in the centre of the Universe and that all the "planets" circled the Earth. The reasons for this perception were that stars and planets appeared to revolve around the Earth each day,^[10] and the apparently common sense perception that the Earth was solid and stable, and that it is not moving but at rest.