eath presents a skull to The Astrologer. Presumably to show a comparison between the spherical universe and the skull.
Above the head of the astrologer hangs a model of the Universe with the Zodiac, which is reminiscent of the picture of The Last Judgment. For further details, see this external link about The Armillary Sphere.
The astrologer does not appear on most of the so-called proofs. In fact he is only known from one single series with "Gothic" black letters, in contrast to the other series that have "ordinary" Roman letters, slightly inclined (see picture above). With the official issue of Les Simulachres & Historiées in Lyon in 1538 the astrologer became an integrated part of the dance of death.
Variations: Birckmann lets the astrologer measure a globe;
the window is made square with a shell-motif above.
Valvasor and Deuchar copy Birckmann.
However, Valvasor ignores the mussel-shell above the window, which shows
that Deuchar has copied Birckmann, and not Valvasor.
Rubens places 2 rulers crosswise on the table, and Mechel replaces them with a real cross.