A Day on Venus Is Longer Than Its Year

The timekeeping on Venus is one of the most bizarre and counterintuitive in our solar system. While Earth's day is a tiny fraction of its year, Venus operates on a completely different scale. The planet completes a single, sluggish rotation on its axis in 243 Earth days, but it finishes its full orbit around the Sun in just 225 Earth days. This creates the unique situation where a Venusian day is longer than a Venusian year. To make things even stranger, Venus has a retrograde rotation, meaning it spins backward compared to Earth and most other planets.

Scientists believe this strange state of affairs is the result of two major factors in the planet's history. The incredibly slow spin is likely caused by its thick, crushing atmosphere. Formed by a runaway greenhouse effect, the atmosphere is so dense that it exerts a powerful drag on the surface, acting like a planetary brake over billions of years. The backward rotation, on the other hand, is thought to be the scar of a cataclysmic impact with a large celestial body early in its history, which could have knocked the planet off-kilter and drastically altered its spin.

This cosmic oddity creates a truly alien (Review) experience. For any potential observer on the surface, the Sun would rise in the west and set in the east. Because of the slow, backward rotation combined with the orbital period, the time between one sunrise and the next—what we would call a solar day—is about 117 Earth days. This means you could watch the Sun slowly creep across the sky for nearly four Earth months before it finally sets again.