In the Solar System, all the planets orbit the Sun in the same direction as the Sun rotates : counter-clockwise as seen from above the Sun's north pole. At least one exoplanet, WASP-17b, has been found to orbit in the opposite direction to its star's rotation. The period of one revolution of a planet's orbit is known as its sidereal period or year. A planet's year depends on its distance from its star; the farther a planet is from its star, the longer the distance it must travel and the slower its speed, since it is less affected by its star's gravity.