Here's why:

* Rotation Period: Venus takes about 243 Earth days to complete one rotation on its axis. This is much slower than Earth's 24-hour rotation.

* Retrograde Rotation: Venus also rotates in the opposite direction compared to most planets, including Earth. This means the sun rises in the west and sets in the east on Venus.

While some dwarf planets may have even slower rotation periods, Venus holds the title for the slowest spinning planet in our solar system.