A comparison of comets

Recently I've been working on extending my examination of practicas (annual astrological prognostications) into the decades beyond what I examined in Printing and Prophecy, or beyond 1550. While I've been looking at later decades, I've noticed that comet booklets turn up intermittently, as do comets, but also that the response can vary wildly. Some comets generate a few editions, while others are the occasion for dozens. The comet of 1618-19, which appeared just as central Europe was sliding into the Thirty Years War, appears to have seen a typographic panic attack of unprecedented proportion. By searching VD16/17 for "comet*" for years that I already knew had 7 or more comet editions, I came up with the following graph:

1531 was Halley's comet, followed in quick succession by the appearance of two other comets in the following years. The comet of 1577 was particularly visible, although it would be worth investigating what about its historical context made comet prognostications such a hot commodity. And the comet of late 1618 is in a class by itself. This graph hardly even counts as preliminary work, of course, but it might point the way to some interesting projects.