In addition to the documentary sources, historians of science have at their disposal other material sources, as well as an interpretative approach of a very particular kind. In cases where a reliable description of an instrument exists, or better still, where the instrument has survived intact and functioning to our own day, the historian of science can use it again to replicate observations made in the past.

This "experimental history of science" is often used to clarify scientific events of dubious authenticity; for example, to determine whether a scientist really made a certain observation or only claimed to have done so. Obviously, no such doubt exists in regard to Galileo’s observations, but in this case experimental history can assume an important explanatory or educational role. Repeating Galileo’s observations through replicas of his telescope aimed at real celestial bodies or at images of them can, in fact, help us to understand the material difficulties of the first telescopic observations, the objective limitations of the instruments used and the technical/practical solutions devised to transform the visual information into data as objective as possible.