thumb|Saturn's Great White Spot in 2011. The Great White Spot, also known as Great White Oval, on Saturn, named by analogy to Jupiter's Great Red Spot, are periodic storms that are large enough to be visible from Earth by telescope by their characteristic white appearance. The spots can be several thousands of kilometers wide. The Cassini orbiter was able to track the 2010–11 instance of the storm, also known as the Northern Electrostatic Disturbance, because of an increase in radio and plasma interference, or the Great Springtime Storm. Cassini data has revealed a loss of acetylene in the white clouds, an increase of phosphine, and an unusual temperature drop in the center of the storm. After the visible aspects of the storm subsided, in 2012, a "belch" of heat and ethylene was emitted from two hotspots that merged. Occurrence The phenomenon is somewhat periodic at 28.5-year intervals, when Saturn's northern hemisphere tilts most toward the Sun. The following is a list of recorded sightings. 1876 – Observed by Asaph Hall. He used the white spots to determine the planet's period of rotation. 1903 – Observed by Edward Barnard. 1933 – Observed by Will Hay, comic actor and amateur astronomer. Until recent times the most celebrated observation. 1960 – Observed by JH Botham (South Africa). 1990 – Observed by Stuart Wilber, from 24 September through November. 1994 – Studied by ground-based observers and the Hubble Space Telescope. 2006 – Observed by Erick Bondoux and Jean-Luc Dauvergne. 2010 – First observed by Anthony Wesley, photographed by Cassini space probe 2010–11. That none were recorded before 1876 is a mystery, in some ways akin to the long observational gap of the Great Red Spot in the 18th and early 19th centuries; the 1876 Great White Spot (GWS) was extremely prominent, being visible in apertures as small as 60 mm. It is not known if the earlier record was simply poor, or if the 1876 GWS was truly a first for the telescopic era. Some believe that neither scenario is likely. In 1992, Mark Kidger described three significant GWS patterns: The GWSs alternate in latitude, with one apparition being limited to the North Temperate Zone (NTZ) or higher, and the following being limited to the Equatorial Zone (EZ). For instance, the 1960 GWS was high-latitude, and the 1990 GWS was equatorial. The high-latitude GWSs recur at a slightly shorter interval than the equatorial GWSs