Babylonian observations of a unique planetary configuration (Q2212348)

In late March of 185 BC, Babylonian astronomers encountered a rare ``massing of the planets''. Shortly before sunrise, all five planets could be seen together. For a week they clustered in a range of the ecliptic comprising less than 10 degrees in longitude. Observational records of the event are preserved in two fragmentary astronomical diaries. One of them, the previously published BM 46051, is a regular diary, containing also non-astronomical materials such as commodity prices, while the new text BM 32562 is unusually short; it extends over about two weeks covering the massing event. The two texts must have been produced by different observers, possibly observing at different locations. The detailed astronomical analysis is by the first author, and the new text will be published by the second author [Astronomical diaries and related texts from Babylonia, Vol. IV. Wien: Verlag der Österreichischen Akademie der Wissenschaften (to be published)]. The present study illustrates several important aspects of the visibility of stars and planets during twilight. It exposes an interesting limitation of Babylonian naked-eye astronomy. The two ancient observers were confused, sometimes differently, about the identity of some planets at their first appearance. Thanks to their characteristic brightness the planets Venus and Jupiter were easy to identify. But Mercury, Mars and Saturn created problems, since they were located close to each other, appeared in time close to each other, and had similar visual magnitudes. Another interesting tidbit is the authors' tentative interpretation of a curious expression used in a damaged context. Elsewhere the expression is used to denote that the Moon is going to cover a star, but this cannot apply here. They propose that the ancient astronomers in this passage correctly predict an extremely rare exact conjunction of Jupiter and Mars occurring on the afternoon of 25 March 185 BC, when the two planets got so close together that they would appear as a single object. The point of interest to be made here is that the ancients would have accurately extrapolated an invisible daytime event from sightings made near preceding sunrises.