A Day On Venus Is Longer Than Its Year

Venus has one of the most unusual rotational patterns in our solar system. The planet rotates in the opposite direction of most planets, a retrograde rotation that makes the Sun rise in the west and set in the east. More remarkably, Venus spins extremely slowly. A sidereal day, the time it takes Venus to complete one full rotation on its axis relative to the stars, lasts 243 Earth days. Meanwhile, Venus orbits the Sun in just 224.7 Earth days. This means a day on Venus is actually longer than a Venusian year. The solar day, measured from noon to noon, is different at 116.75 Earth days due to the planets retrograde rotation and orbital motion. Scientists are not entirely certain why Venus rotates this way, though one leading theory suggests a massive collision with a planetesimal early in the planets formation may have tipped it over and slowed its spin. Venus also rotates in such a way that it presents almost the same face toward Earth at each closest approach, due to a gravitational resonance between the two planets.