The purpose of this article is to correct the generally held impression that the metaphor ‘aurora borealis’ (northern dawn) originated with Gassendi in 1621. The first published use of it by Gassendi actually apeared in 1649 in a passage describing an auroral display that he observed in 1621. The metaphor appeared 30 years earlier, in 1619, in a work at least partially and probably completely authored by Galileo. We argue here that its appearance in this work, ‘Discourse on the Comets,’ is the origin of the metaphor.