How Long Is A Day On Venus?
QUICK ANSWER
Venus rotates once on its axis every 243 Earth days, making it the slowest-rotating planet in our solar system. That's longer than Venus's year, which is only 225 Earth days. A solar day on Venus (sunrise to sunrise) lasts about 117 Earth days because Venus rotates in the opposite direction from most planets.
Venus has one of the strangest day-and-year situations in the solar system. The planet rotates so slowly that a single rotation takes longer than a complete orbit of the Sun. And when you account for that rotation going the wrong direction, the math gets even weirder.
How long does Venus take to rotate?
Venus rotates once on its axis every 243 Earth days, according to NASA. That's the sidereal day, measured against the distant stars. It makes Venus the slowest-rotating planet in our solar system. For comparison, Earth rotates once every 24 hours, and even Mercury (next slowest) takes only 59 Earth days. Venus's rotation is so slow that the surface barely moves over the course of an Earth week.
How long is a day from sunrise to sunrise on Venus?
About 117 Earth days. This is the solar day, the time from one sunrise to the next at any spot on Venus. It's shorter than Venus's rotation period because the planet rotates backwards. The retrograde rotation means that as Venus turns slowly one direction and orbits the Sun in the other direction, the two motions combine to bring the Sun back overhead faster than rotation alone. The Sun rises in the west and sets in the east on Venus.
Is a day on Venus really longer than a year?
Yes, if you measure a day by full rotation against the stars. Venus's rotation period is 243 Earth days, and its orbital period is 225 Earth days, so technically one Venusian day (sidereal) is longer than one Venusian year. Venus is the only planet where this is true. If you measure a day by sunrise-to-sunrise, the solar day is shorter than the year, which makes more practical sense. The point is that on Venus, the concept of a day is genuinely strange.
Why does Venus rotate so slowly?
The leading theory is that Venus's thick atmosphere has acted as a brake over billions of years. Atmospheric tides, caused by the Sun's gravity acting on Venus's dense air, slowly drained rotational energy from the planet. Combined with the possibility of an ancient impact that knocked Venus off-kilter, the result is the unusual slow rotation we see today. The atmosphere also rotates separately from the surface, completing a full circuit in about 4 Earth days.
Venus rotates slower than any other planet, with a single rotation taking 243 Earth days, longer than its 225-day year. Combined with retrograde rotation and a thick atmosphere that spins independently, Venus's timekeeping is genuinely unique. On the surface, the Sun rises in the west, moves slowly across the sky, and sets in the east, four Earth months later.
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