  In the middle of the seventeenth century, Andr\'e Tacquet, S.J. briefly
discussed a scientific argument regarding the structure of a Copernican
universe, and commented on Galileo Galilei's discussion of that same argument
-- Galileo's discussion in turn being a commentary on a version of the argument
by Christoph Scheiner, S.J. The argument was based on observations of the sizes
of stars. This exchange involving Galileo and two Jesuits illustrates how
through much of the seventeenth century, science -- meaning observations
measurements, and calculations -- supported a view of the Copernican universe
in which stars were not other suns, but were dim bodies, far larger than the
sun. Johannes Kepler emphasized this, especially in arguing against Giordano
Bruno. Jesuit astronomers like Tacquet and Scheiner understood this. Those who
might have listened to Jesuit astronomers would likewise have understood this
-- Robert Bellarmine, for example, whose role in the debate over Copernicanism
is well known. To many, such a universe was, in the words of Galileo's Dialogue
character Sagredo, "beyond belief," and no modern view of a universe of many
distant suns would be scientifically supportable until after Tacquet's death in
1660. The Copernican universe of the seventeenth century looked radically
different from the universe as modern astronomers understand it, and
recognizing this fact allows for interesting questions to be asked regarding
the actions of those, such as Bellarmine, who were responding to the work of
Copernicus.
