Saturn's hexagon is a persisting hexagonal cloud pattern around the north pole of Saturn, located at about 78°N. The sides of the hexagon are about 13,800 km (8,600 mi) long, which is longer than the Earth's diameter. It rotates with a period of 10h 39m 24s, the same period as Saturn's radio emissions from its interior. However, the hexagon does not shift in longitude like other clouds in the visible atmosphere.
Saturn's south pole does not have a hexagon, according to Hubble observations. But it does have a vortex, and there is also a vortex inside the northern hexagon.
Saturn's polar hexagon discovery was made by the Voyager mission in 1981--82, and it was revisited since 2006 by the Cassini mission. Cassini was only able to take thermal infrared images of the hexagon, until it started to become visible by light in January 2009. Cassini also recently was able to take a video of the hexagonal weather pattern, while traveling at the same speed as the planet, therefore recording only the movement of the hexagon.
Hexagon on Saturn