8:12 And the fourth angel sounded, and a third of the sun and a third of the moon and a third of the stars were smitten, so that a third of them might be darkened and the day might not shine for a third of it, and the night in the same way.

and the FOURTH ANGEL sounded, and

This trumpet alters the amount of light the earth receives to one third less than what is normal now. Since the earth revolves around the sun, having listed the SUN, MOON, and STARS in equal THIRDs indicates that they did not change their positions, but rather, something on earth changed just that we see this change to our surrounding cosmos.

so that a THIRD of them might be darkened and the DAY might not shine for a THIRD of it, and the NIGHT in the same way.

If a third trumpet was a cosmic impact with the earth, the rotation of the earth could be sped up such that the days and nights would be a third shorter than what they are now. That is, the earth would make a complete revolution on its axis every 16 hours instead of 24. It would be an interesting calculation to determine the size of the invading cosmic object which would cause the earth to increase its angular momentum by that much.

It is interesting that this is put into THIRDs. This keeps this verse "season" neutral. That is, the DAYLIGHT and NIGHTTIME is a different length depending whether it is winter or summer, for example. But using THIRDs will work no matter what day of the year one is talking about. Recall Jesus' words in Mark 13:32-37.

Let's look at the expression 'might be darkened'. There was darkness in one the of plagues on Egypt in Exodus 10:21-23. The darkness was so thick you could feel it, and, curiously, the Israelis light worked while the Egyptians didn't (implied). This Egyptian darkness was for three days and then, apparently, the normal day/night cycle returned. In this fourth TRUMPET, this appears to be a permanent effect on the earth's rotation.

At Christ's crucifixion, darkness fell upon the land for 3 hours from noon until 3 pm as given in Matthew 27:45. This was a one time occurrence on that day.

From a symbolic view, darkening of the sky is connected with the appearing of God's judgment.

Darkening the sky ... appearance of God's Judgment
Isaiah 13:9-13 Punish the world for its evil.
Ezekiel 32:7-8 Cover the heavens and darken the stars.
Joel 2:10-11 Sun and moon grow dark.
Joel 3:14-15 Valley of God's verdict see sun and moon grow dark.
Matthew 24:29-31 After tribulation of those days ...

As a footnote, most crimes are committed in darkness. Does this imply the number of crimes will go up by 33%?