Complex sentence: The reverse side shows an image of Johannes Kepler who was a personal friend of Hans Ulrich who taught at the former Protestant school in Graz and whose mathematical and celestial observations likely had an impact on the symbolism of the design of the palace.
Split into simpler sentences: The reverse side shows an image of Johannes Kepler who was a personal friend of Hans Ulrich and who taught at the former Protestant school in Graz. His mathematical and celestial observations likely had an impact on the symbolism of the design of the palace.