Tycho Brahe
However, no mention of the Tycho Brahe days is actually found in the work of Tycho Brahe. They nevertheless are often referenced in almanacs and recur in Scandinavian folklore. In the Cyprianus tradition, Tycho Brahe days are considered unlucky for magical work; several of the spells in the "Black Books of Elverum" note that they should not be carried out on a Tycho Brahe day.