It seems that apparently, Revelation 8:12 is about the 536 a.d. catastrophes that went on causing havoc on the earth including the black plague....(otherwise known as "WORMWOOD"??).
Rev 8:11 The name of the star is Wormwood . A third of the waters became Wormwood , and many men died of the water, because it was made bitter.
Revelation 8:12 The fourth angel blew his trumpet, and a third of the sun was struck, and a third of the moon, and a third of the stars, so that a third of their light was darkened; a third of the day was kept from shining, and likewise a third of the night.