The sidereal messenger of Galileo Galilei and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries (1880)
nheavenlybodies by thesize of theaperture ofthe telescope. For the sake of being more easily understood, Iwill suppose a tube abcd.1 Let e be the eye of theobserver; then, when there are no lenses in thetube rays from the eye to the object f G would bedrawn in the straight lines E c F, E D G, but… … The line c h in Galileos figure represents the small pencil of raysfrom h which, after refraction through the telescope, reach the eye E.The enlarged figure shows that if op be the radius of the apertureemployed, the point h of the object would be just outside the field ofview. The method, however,…
Astronomy
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