What does Mark 13:25 mean?

The note about the stars and the heavenly powers is tricky to interpret. Given metaphors found in other Scripture, God's power over creation, and modern technology, there are at least three different options.

One option is that Jesus is explaining now-modern technology using terms the first century disciples will understand. A nuclear winter might cause debris to fill the atmosphere so that the light from the sun, moon, and stars is dimmed. "Stars" falling could be satellites which cause the "powers," or earthly rulers, to lose command, control, and communication over their forces. Or the stars could be the nuclear missiles, themselves.

Another option is that God is exerting His power over creation, as He has throughout the ages, and the meaning is explicitly literal. In Joshua 10:12–14, Joshua asked God to extend the day so the Israelites could finish the battle against the Amorites. God did so for about a full day. When God agreed to allow King Hezekiah to recover from his illness, He caused a shadow to retreat ten steps as a sign (2 Kings 20:1–11). When Korah disobeyed God, the earth swallowed him and his family (Numbers 16:31–33). As Creator, God would have no problem causing a natural disaster to fit this description. Although stars couldn't literally fall to earth, asteroids and comets could. Others think the forces of nature will be so unsettled that physics, itself, will fail, and the stars and planets will lose their orbits. With God's all-encompassing power and authority, there's no reason this couldn't happen.

Yet another option is that this verse describes the fall of evil spiritual forces. When Isaiah 14:12 talks about a fallen star, it means Satan. Isaiah 34:4 and Revelation 6:13 speak about the host of heaven falling. The powers in the heavens are demonic forces that exist in the spirit world but have influence on Earth. Ephesians 6:12 mentions "spiritual forces of evil in the heavenly places." "Powers" is from the Greek root word dunamis and can mean the power of an army. "Heavens" is from the Greek root word Ouranos which can mean the sky or the spiritual realm of angels and demons. Furthermore, "falling" is from the Greek root word pipto which can mean physically falling, falling prostrate in submission and fear, or being removed from power. So, this is also a viable option.

The passage isn't specific enough to say conclusively what the stars and powers are or how, exactly, they will fall and shake. It's possible that all three will happen.