Charles Ellicott Commentary Acts 2:20

"The sun shall be turned into darkness, And the moon into blood, Before the day of the Lord come, That great and notable [day]." — Acts 2:20 (ASV)

The sun shall be turned into darkness.—Both clauses bring before us the phenomena of an eclipse: the total darkness of the sun, the dusky copper hue of the moon. Signs, of which these were but faint images, had been predicted by our Lord, echoing, as it were, the words of Joel, as among the preludes of His Advent (Matthew 24:29).

That great and notable day.—St. Luke follows the LXX version. The Hebrew gives, as in our version, the great and terrible day. As seen by the prophet, the day was terrible to the enemies of God; a day of blessing to the remnant whom the Lord should call (Joel 2:32). The Greek word for “notable” (epiphanès) lent itself readily to the thought of the great Epiphany or manifestation of Christ as the Judge of all.