The moon wears a crown: Babylonian reports of earthshine

Abstract

AbstractObservations of the first visibility of the new moon crescent by ancient Babylonian astronomers often refer to the moon “wearing a crown”. In this article, we undertake a detailed analysis of all Babylonian reports of the observation of the new moon crescent in order to test the common assumption that this phrase refers to the phenomenon of Earthshine. We conclude that the assumption is correct and further explore the observational circumstances that made Earthshine visible to the Babylonian astronomers—and by analogy to any experienced naked‐eye observer. We demonstrate that the most significant factor in whether or not Earthshine is seen is not, as might be expected, the age of the moon but instead the prevailing sky darkness. We also show that the Babylonian observations display a seasonal variation that is consistent with modern observations of and models for the Earth's albedo.