On Venus, the Sun rises in the west and sets in the east
Almost all major planets spin in a counterclockwise direction on their axes. Venus is a rare exception: it rotates clockwise in a motion called retrograde rotation. Because of this reverse spin, a hypothetical observer on the cloud-shrouded surface of Venus would watch the Sun rise in the west each morning and set in the east every evening.
A Solar System Anomaly
In the early formation of the Solar System, the vast disk of gas and dust collapsing around the newborn Sun established a prevailing direction of motion. As matter clumped together to form the planets, conservation of angular momentum ensured that most bodies orbited the Sun counterclockwise when viewed from above the Sun's north pole. Furthermore, almost every planet inherited this same counterclockwise spin on its own internal axis, a motion known in astronomy as prograde rotation.
Venus stands out as a stark exception among the major terrestrial planets. Rather than spinning in the standard counterclockwise direction, Venus rotates clockwise, an orientation termed retrograde rotation. For a hypothetical observer standing beneath the planet's dense veil of clouds, this backward spin would completely invert the familiar celestial mechanics experienced on Earth. Instead of watching the Sun climb into the morning sky from the eastern horizon, sunrise on Venus occurs in the west, with sunset taking place in the east.
Sidereal Days and the Synodic Paradox
The unusual spin of Venus creates an extraordinary relationship between the length of its day and the length of its year. Venus rotates on its axis at an exceptionally sluggish pace, requiring roughly 243 Earth days to complete a single rotation relative to the distant stars. This period, known as the sidereal day, is the slowest rotation rate of any planet in the Solar System. In fact, Venus takes longer to complete one axial rotation than it takes to complete an entire orbit around the Sun, which lasts approximately 224.7 Earth days.
However, the apparent motion of the Sun across the Venusian sky—the solar day, or synodic day—does not match its 243-day sidereal rotation. Because Venus travels forward in its orbit around the Sun while simultaneously spinning backward on its axis, the two motions combine to compress the day-night cycle. As a result, the time elapsed between one sunrise and the next is roughly 116.75 Earth days. Consequently, a single Venusian year contains fewer than two full solar days, producing prolonged periods of daylight followed by equally extended stretches of night.