Charles Ellicott Commentary Joel 2:30-31

"And I will show wonders in the heavens and in the earth: blood, and fire, and pillars of smoke. The sun shall be turned into darkness, and the moon into blood, before the great and terrible day of Jehovah cometh." — Joel 2:30-31 (ASV)

The sun ... and the moon.— These words, recalling some of the signs in the ancient history of the Jews (especially as seen in some of the plagues of Egypt), are used by our Lord Himself as heralding the great day of judgment. They are echoed again by Saint John in the vision of the opening of the sixth seal: “For the great day of His wrath is come, and who shall be able to stand?” (Compare Joel 2:11, also in this chapter.) The sun and moon, etc., may include the luminaries in heaven and the rulers on earth.