Revelation 8:12,13

12 And the fourth angel sounded, and the third part of the sun was smitten, and the third part of the moon, and the third part of the stars; so as the third part of them was darkened, and the day shone not for a third part of it, and the night likewise.

After Wormwood hits the earth it will throw up huge amounts of debris and smoke into the atmosphere so that the sun, moon and sky become darkened on this third of the earth.

13 And I beheld, and heard an angel flying through the midst of heaven, saying with a loud voice, Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the trumpet of the three angels, which are yet to sound!

Before the fifth angel blows the trumpet, John sees an angel flying in the atmosphere telling those on earth that there are three woes yet to come. These will be announced by the last three trumpet blasts.

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