Objects In Telescope Are Farther Than They Appear: How diffraction tricked Galileo into mismeasuring the distances to the stars

TL;DR

Galileo's measurements of stellar distances were significantly underestimated because he was misled by diffraction artifacts in his telescope, which affected the apparent sizes of stars he observed.

Contribution

This paper reveals that Galileo's star distance measurements were based on diffraction artifacts, highlighting a historical misconception in early astronomical observations.

Findings

Galileo's star size measurements were affected by diffraction.

Diffraction artifacts led to underestimation of stellar distances.

Historical astronomical data need re-evaluation considering optical effects.

Abstract

Galileo determined distances to stars based on the assumption that stars were suns, the apparent sizes of stars as seen through his telescope, and basic geometry. However, the apparent sizes that he measured were the result of diffraction and not related to the actual sizes of the stars. Galileo's methods and observations were good, but since he was unknowingly observing diffraction artifacts and not the physical bodies of stars he greatly underestimated the distances to the stars.