Kepler’s star map shows the constellations of Ophiuchus (the Serpent Handler), Sagittarius and Scorpius. The Milky Way runs diagonally down from the left, and the “ecliptic,” or annual path of the Sun, runs horizontally through Sagittarius and Scorpius.
A triple conjunction of Jupiter and Saturn took place in 1603, followed by a planetary massing with Mars in 1604. After the planetary massing, a “Nova” or bright star (“N”) suddenly appeared in the ankle of Ophiuchus on October 10, 1604.
The new star was no ordinary star; it remained visible even in the daytime sky for over a year. The new star prompted widespread debate about what it might portend and whether the heavens could change. Now called Kepler’s nova, it was the second supernova to be observed in a generation, after the supernova in Cassiopeia, described by Tycho, which appeared in 1572. No supernova within the Milky Way galaxy has been observed since.
Kepler’s star positions and artistic style show the influence of Tycho and Bayer. Bayer had reversed a number of constellation figures, including Orion and Ophiuchus. In contrast, Kepler’s map shows the figure of Ophiuchus facing toward us rather than outward, so that the traditional star names of his feet and shoulders match the orientation of the constellation figure.
Aristotle taught that conjunctions and planetary massings produce comets. Here, less ominously, they seemed to have produced a new star. Kepler mused that this new star might have been caused by the planets’ proximity, might portend the fall of the Turks, or perhaps the second advent of Christ. Above all, he forecast that it would result in good business for booksellers, as a rash of hastily produced pamphlets would be rushed into print to explain it! Or maybe, he wondered, something similar might have happened for the Bethlehem Star. Some variation of Kepler’s account is the most common explanation of the Star of Bethlehem offered in planetarium shows and astronomer talks today.
In this book, Kepler also discussed mathematical chronology, the date of the birth of Christ, and the nature of the Star of Bethlehem.