All the planets of the Solar System orbit the Sun in an anti-clockwise direction as viewed from above Earth’s north pole. Most planets also rotate on their axes in an anti-clockwise direction, but Venus rotates clockwise (called “retrograde” rotation) once every 243 Earth days—the slowest rotation period of any planet. Because its rotation is so slow, it is highly spherical.[76] A Venusian sidereal day thus lasts longer than a Venusian year (243 versus 224.7 Earth days). Venus’s equator rotates at 6.5 km/h (4.0 mph), whereas Earth’s is approximately 1,670 km/h (1,040 mph).[77] Venus’s rotation has slowed down by 6.5 min per Venusian sidereal day since the Magellan spacecraft visited it 16 years ago.[78] Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury’s 176 Earth days); one Venusian year is about 1.92 Venusian (solar) days long.[79] To an observer on the surface of Venus, the Sun would rise in the west and set in the east.[79]