Joel's prophecy that the moon will be turned to blood appears in a list of portents (3:3–4 Heb.; 2:30–31 Eng.). Scholarly interpretations of this lunar phenomenon usually explain it as a discoloration caused by either voluminous smoke and dust or a lunar eclipse. An examination of the word מוֹפְּתִים ("portents"), however, indicates that the celestial transformation requires something more dramatic. This article argues that a theory by astronomer Danny Faulkner makes better sense of the event and the context of Joel than extant theories. Faulkner posits that Joel described a dried-blood color lunar eclipse. Historical and scientific research explains that dark-brown lunar eclipses were considered omens of famine and unrest. Furthermore, an especially dark lunar eclipse fits the parallel passages in Joel 2:10 and 4:15 Heb.; 3:15 Eng. as well as the context of temple sacrifice found in the book.