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Since the dawn of telescopic astronomy astronomers have observed and measured the "spurious" telescopic disks of stars, generally reporting that brighter stars have larger disks than fainter stars.Early observers such as Galileo Galilei interpreted these disks as being the physical bodies of stars; later observers such as William Herschel understood them to be spurious; some, such as Christian Huygens, argued that stars show no disks at all. In the early 19th century George B. Airy produced a theoretical explanation of star images sufficient to explain all historical observations, but astronomers were slow to fully recognize this. Even today conventional wisdom concerning stars and telescopes stands at odds to both historical observations and Airy"s theory.We give a detailed analysis of both historical observations and Airy"s theory, illustrating how Airy"s theory explains the historical observations, from Galileo to Huygens to Herschel. We argue that the observations themselves appear in all cases to be valid and worth further study.2 3

Setting aside all authority : Giovanni Battista Riccioli and the science against Copernicus in the age of Galileo / Christopher M. Graney. pages cm Includes bibliographical references and index.

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Because early telescopic astronomers did not understand the spurious nature of star images formed by their telescopes, their observations of the stars yielded data that apparently confirmed the geocentric Tychonic world system. Both Galileo Galilei (1564-1642) and Simon Marius (1570-1624) obtained such data. Galileo backed Nicholas Copernicus (1473-1543) despite his data. Marius supported Tycho Brahe (1546-1601) on the basis of his data.