11 The name of the star is Wormwood, and a third of the waters became wormwood. So, many of the people died from the waters, because they had been made bitter.
A massive meteorite caused the waters to become poisonous and those who drank the water died. Most likely thousands of houses were getting their drinking water from the source that got contaminated.
12 The fourth angel blew his trumpet, and a third of the sun was struck, a third of the moon, and a third of the stars, so that a third of them were darkened. A third of the day was without light, and the night as well.
The likely scenario that would darken the sun, moon, and stars would be clouds of debris from the impact of the meteorites bombardments which will rise up to the sky and block most of the light from shining on the people.
13 I looked again and heard an eagle flying high overhead, crying out in a loud voice, “Woe! Woe! Woe to those who live on the earth, because of the remaining trumpet blasts that the three angels are about to sound!”
The phrase “heard an eagle flying high overhead” could refer to an angel that has wings and thus calling it an eagle.
Angels are going to participate in spreading the gospel and warning those who have survived their impending doom for most of them. The angel is trying to get them to realize something worse is coming and they need to repent, like now.