Article ID: CBB926402888

Giles of Lessines on Starlight and the Colour of the Sky (2021)

unapi

This article provides the first discussion of the unpublished treatise De crepusculis (“On twilight”), written in the second half of the thirteenth century by the Dominican scholar Giles of Lessines. It is shown that De crepusculis was intended as a critical supplement to a treatise on the height of the atmosphere by Ibn Muʿādh (eleventh century). In this supplement, Giles recapitulates Ibn Muʿādh’s geometrical arguments while furnishing proofs and covering relevant questions not included in the earlier work. One area where Giles greatly expands on his predecessor is in addressing relevant physical questions such as the causes of stellar luminosity. Giles here takes a nuanced view, acknowledging that all celestial bodies emit some form of light. He also provides a unique explanation of the blue colour of the sky, which draws on the extramission postulate used by thirteenth-century writers on optics.

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Authors & Contributors
Mozaffari, S. Mohammad
Rupa, K.
Venugopal, Padmaja
Bònoli, Fabrizio
Darrigol, Olivier
El-Bizri, Nader
Journals
Journal for the History of Astronomy
Journal of Astronomical History and Heritage
Centaurus: International Magazine of the History of Mathematics, Science, and Technology
Archive for History of Exact Sciences
History and Technology
Science in Context
Publishers
Cambridge University Press
William Morrow
Concepts
Celestial mechanics
Astronomy
Earth (planet)
Stars; stellar astronomy
Light
Optics
People
Grosseteste, Robert
Newton, Isaac
Ptolemy
Albertus Magnus
al-Bīrūnī, Muḥammad ibn Aḥmad
al-Jayyani, Abu ‘Abd Allah Muhammad Ibn Mu'adh
Time Periods
Medieval
Ancient
18th century
Renaissance
Early modern
13th century
Places
India
Middle and Near East
Rome (Italy)
Europe
Greece
Institutions
Università di Bologna
Royal Society of London
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