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The Great Red Spot is a persistent Anticyclonic Storm on the Planet Jupiter , 22° south of the equator, which has lasted for at least - 1830}} years and possibly as long as - 1665}} years or more. The storm is large enough to be visible through Earth -based Telescope s. It was probably first observed by Giovanni Domenico Cassini , who described it around 1665. The spot has been noticeably red at times throughout its observed history yet has not been appreciably red in the visible spectrum since a rather brief period in the mid 1970's. Storms such as this are not uncommon within the Turbulent Atmospheres of Gas Giant s. Jupiter also has white ovals and brown ovals, which are lesser unnamed storms. White ovals tend to consist of relatively cool clouds within the upper atmosphere. Brown ovals are warmer and located within the "normal cloud layer." Such storms can last hours or centuries. Before the Voyager missions, astronomers were highly uncertain of the Red Spot's nature. Many believed it to be a solid or liquid feature on Jupiter's surface. OBSERVATION HISTORY The Great Red Spot appears at first to be remarkably stable, and most sources concur that it has been continuously observed for 300 years. However, the situation is more complex than that; the present spot was first seen only after 1830 and well-studied only after a prominent apparition in 1879. A long gap separates its period of current study after 1830 from its seventeenth-century discovery; whether the original spot dissipated and re-formed, whether it faded, or even if the observational record was simply poor are all unknown. By way of example, its first sighting is often credited to Robert Hooke , who described a spot on the planet in May 1664; however, it is likely that Hooke's spot was in the wrong belt altogether (the North Equatorial Belt, versus the current Great Red Spot's location in the South Equatorial Belt). Much more convincing is Giovanni Cassini 's description of a "permanent spot" the following year.Rogers (1995), 6. With fluctuations in visibility, Cassini's spot was observed from 1665 to 1713; however, its shorter length and slower motion than the modern spot, along with an 118-year observational gap, make its identification with the Red Spot impossible to determine.Rogers (1995), 188. |
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