Acts 2:20

The sun shall be turned into darkness
As at the death of Christ, by a total eclipse of it:

and the moon into blood;
as at the opening of the sixth seal, ( Revelation 6:12 )

before that great and notable day of the Lord come;
when he shall come in power and great glory, as he did in a few years after this, to take vengeance on the Jews, and destroy their nation, city, and temple; in which there was a display of his greatness, and power, and which was awful and "terrible" to them, as in Joel it is called; (See Gill on Matthew 24:29).