The planet with the longest day in the solar system is Venus. A single rotation on Venus takes about 243 Earth days, making its day longer than its year, which is approximately 225 Earth days. Furthermore, Venus rotates in the opposite direction to most planets in the solar system (retrograde rotation), meaning that on Venus, the Sun rises in the west and sets in the east. This unusual rotational period, along with its thick, toxic atmosphere and intense surface pressure, makes Venus a fascinating yet extreme environment in our solar system.