Interpreting the Visual Evidence

Astronomical Observations and the Mapping of the Heavens

One (often-repeated) nar rative about the scientific revolution is that it marked a crucial break separating modern science from an earlier period permeated by an atmosphere of superstition and theological speculation. In fact, medieval scholars tried hard to come up with empirical evidence for beliefs that their faith told them must be true, and without these traditions of observation, scientists like Copernicus would never have been led to propose alternative cosmologies (see "Ptolemaic Astronomical Instruments" on page 495).

The assumption, therefore, that the "new" sciences of the seventeenth century marked an extraordinary rupture with a more ignorant or superstitious past is thus not entirely correct. It would be closer to the truth to suggest that works such as that of Copernicus or Galileo provided a new context for assessing the relationship between observations and knowledge that came from other sources. Printed materials provided opportunities for early modern scientists to learn as much from each other as from more ancient sources.

The illustrations here are from scientific works on astronomy both before and after the appearance of Copernicus's work. All of them were based on some form of observation and claimed to be descriptive of the existing universe. Compare the abstract illustrations of the Ptolemaic (image A) and Copernican (image B) universes with Tycho Brahe's (image C) attempt to reconcile heliocentric observations with geocentric assumptions, or with Galileo's illustration of sunspots (image D) observed through a telescope.


Questions for Analysis

1. What do these illustrations tell us about the relationship between knowledge and observation in sixteenthand seventeenth-century science? What kinds of knowledge were necessary to produce these images?
2. Are the illustrations A and B intended to be visually accurate, in the sense that they represent what the eye sees? Can one say the same of D? What makes Galileo’s illustration of the sunspots different from the others?
3. Are the assumptions about observation contained in Galileo’s drawing of sunspots (D) applicable to other sciences such as biology or chemistry? How so?

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