Early Astronomy in the University of Michigan Collections

De Maculis

This engraving records a series of telescopic observations of the Sun from December 10 to January 12, 1611. For instance, during the first four days, each of the diagrams shows the position of Venus in conjunction with the Sun. Specifically, the line CD is the path of Venus across the Sun, slightly inclined to the ecliptic AB. On the first day, Venus is carried to D; on the second, it is carried to E; and on the last day, it is carried to F. As the illustrations show, sunspots of various irregular shapes and sizes, rarely spherical, appear in different locations on each diagram. Marked with Greek letters, some of these sunspots can be followed in the course of a few days. For instance, the spot named as Ω was first observed on December 10 at ten o’clock, and last seen on December 24 at eleven o’clock. The wide space between the first and last locations of Ω, a path coinciding with the ecliptic AB, suggests that this particular spot traveled under the Sun at least for 16 days.

On Sunspots

De Maculis: Engraving


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