Venus has the longest planetary day in the Solar System, with one rotation taking about 243 Earth days. This rotational period is longer than Venus’s 225-Earth-day orbital year.
Venus rotates very slowly and in the opposite direction to most planets, a motion called retrograde rotation. As a result, the Sun would appear to rise in the west and set in the east for an observer on its surface. The exact length of a solar day differs from the sidereal rotation period because Venus is also moving around the Sun; a Venusian solar day lasts about 117 Earth days.
Venus is similar to Earth in size and composition but has a radically different surface environment. Its dense carbon-dioxide atmosphere produces a runaway greenhouse effect, making it the hottest planet at the surface, even hotter than Mercury. Thick clouds of sulfuric acid obscure the surface from ordinary visible-light observation.