Page "Pope Callixtus III" Paragraph 10

According to one story that first appeared in a 1475 posthumous biography and was subsequently embellished and popularized by Pierre-Simon Laplace, Callixtus III excommunicated the 1456 apparition of Halley's Comet, believing it to be an ill omen for the Christian defenders of Belgrade from the besieging armies of the Ottoman Empire.

No known primary source supports the authenticity of this account.

The 29 June 1456 papal bull of Callixtus III calling for a public prayer for the success of the crusade, makes no mention of the comet.

By 6 August, when the Turkish siege was broken the comet had not been visible in either Europe or Turkey for several weeks.