The length of a sidereal day on Venus is about 243 Earth days. A sidereal day measures one complete rotation relative to distant stars, rather than the time between successive sunrises. Venus rotates exceptionally slowly and in the opposite direction to most planets, a motion called retrograde rotation.
Venus’s rotation is so slow that its sidereal day is actually longer than its year. Venus completes one orbit around the Sun in about 224.7 Earth days, so the planet turns once on its axis only after its orbit is already complete.
The distinction between sidereal and solar day causes much of the confusion surrounding Venus. Because Venus rotates retrograde while orbiting the Sun, the interval from one sunrise to the next is about 116.75 Earth days—much shorter than its 243-day sidereal rotation period. Both figures can be correct, but they describe different measurements.
Venus’s slow rotation is also linked to its unusual planetary behavior. It has no natural moon, a dense carbon-dioxide atmosphere, and surface temperatures hot enough to melt lead. Its bright cloud cover makes the planet striking in the sky, while radar has been needed to map the hidden surface.