"In the shape of a cooking pot over the fire": Records of solar prominences in the 1180s.

The second half of the 1180s witnessed an unusual number of solar eclipses visible within Europe in quick succession. These were recorded or referenced in a wide range of sources, from chronicles in Latin and Old Church Slavonic to the earliest epic poem from the medieval Rus'. A comparison between key elements of these accounts reveals several notable features. First, the identification of solar prominences. The account of the 1185 total eclipse from the Rus' Laurentian Chronicle is well established in this context as the first probable textual witness to the phenomenon in Europe. It may not be the only one, however. A similar identification can be made within a Latin chronicle from England, by Gervase, monk of the community at Christ Church Cathedral Priory, for the total eclipse of 1187. Second, the contemporaneous nature of the descriptions is noteworthy, and more so in comparison with other contemporary accounts. A third area for focus concerns the nature of the observations and a case-study of Gervase of Canterbury who, if not an eye-witness to what he records, includes generally accurate accounts. These make his occasional inaccuracies all the more intriguing. Fourth, the wider comparison highlights the importance of taking account historical records across the European medieval heritage, Slavic and Orthodox alongside Latin and Catholic traditions.

'The moon quivered like a snake': A medieval chronicler, lunar explosions, and a puzzle for modern interpretation.

Despite some scepticism, the suggestion by Hartung in 1976 that the report in the chronicle of Gervase of Canterbury corresponded to a meteorite impact with the moon in 1178, creating the Giordano Bruno crater, retains considerable support, particularly in popular scientific writing. Nevertheless, a series of studies of images of the crater from orbiting satellites, although confirming its young geological age, have indicated that it was not created within recorded human history. In this paper, we examine astronomical entries in Gervase's chronicle relating to eclipses and conclude that, despite there being descriptions of miracles elsewhere in the manuscript, he himself was a reliable reporter of astronomical events. On this basis an alternative suggestion can be put forward for the splitting of the horns and writhing of the body of the new moon, reported to Gervase: atmospheric turbulence. Although general atmospheric turbulence has been previously dismissed as too small an effect, it is possible to show that the description is consistent with viewing the new moon through a column of hot air from a fire, at a moderate distance and out of the line of sight of the observers. This interpretation of the medieval evidence as credible but unrelated to a lunar event is consistent with twenty-first century lunar studies.

Bow-shaped caustics from conical prisms: a 13th-century account of rainbow formation from Robert Grosseteste's De iride.

The rainbow has been the subject of discussion across a variety of historical periods and cultures, and numerous optical explanations have been suggested. Here, we further explore the scientific treatise De iride [On the Rainbow] written by Robert Grosseteste in the 13th century. Attempting to account for the shape of the rainbow, Grosseteste bases his explanation on the optical properties of transparent cones, which he claims can give rise to arc-shaped projections through refraction. By stating that atmospheric phenomena are reducible to the geometric optics of a conical prism, the De iride lays out a coherent and testable hypothesis. Through both physical experiment and physics-based simulation, we present a novel characterization of cone-light interactions, demonstrating that transparent cones do indeed give rise to bow-shaped caustics-a nonintuitive phenomenon that suggests Grosseteste's theory of the rainbow is likely to have been grounded in observation.

Color-coordinate system from a 13th-century account of rainbows.

We present a new analysis of Robert Grosseteste's account of color in his treatise De iride (On the Rainbow), dating from the early 13th century. The work explores color within the 3D framework set out in Grosseteste's De colore [see J. Opt. Soc. Am. A29, A346 (2012)], but now links the axes of variation to observable properties of rainbows. We combine a modern understanding of the physics of rainbows and of human color perception to resolve the linguistic ambiguities of the medieval text and to interpret Grosseteste's key terms.

A three-dimensional color space from the 13th century.

We present a new commentary on Robert Grosseteste's De colore, a short treatise that dates from the early 13th century, in which Grosseteste constructs a linguistic combinatorial account of color. In contrast to other commentaries (e.g., Kuehni & Schwarz, Color Ordered: A Survey of Color Order Systems from Antiquity to the Present, 2007, p. 36), we argue that the color space described by Grosseteste is explicitly three-dimensional. We seek the appropriate translation of Grosseteste's key terms, making reference both to Grosseteste's other works and the broader intellectual context of the 13th century, and to modern color spaces.