The Discourse on Comets (Italian: Discorso delle Comete) was a pamphlet published in 1619 with Mario Guiducci as the named author, though in reality it was mostly the work of Galileo Galilei. In it Galileo conjectured that comets were not physical bodies but atmospheric effects like the aurora borealis.
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This article is an automated import of the Wikipedia article "Discourse on Comets", available at https://en.wikipedia.org/wiki/Discourse_on_Comets . Text is licensed under CC BY-SA 4.0.