Great Red Spot

The Great Red Spot is a persistent zone of high pressure, producing an anticyclonic storm on the planet Jupiter, 22° south of the equator. It has been continuously observed for 187 years, since 1830. Earlier observations from 1665 to 1713 are believed to have been the same storm; if this is correct, it has existed for more than 350 years. Storms such as this are not uncommon within the turbulent atmospheres of gas giants.

The Great Red Spot (GRS) may have existed since before 1665, but 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.

For 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. With fluctuations in visibility, Cassini's spot was observed from 1665 to 1713; however, the 118-year observational gap makes the identity of the two spots inconclusive, and the older spot's shorter observational history and slower motion than the modern spot make their identity unlikely.

A minor mystery concerns a Jovian spot depicted in a 1711 canvas by Donato Creti, which is exhibited in the Vatican. Part of a series of panels in which different (magnified) heavenly bodies serve as backdrops for various Italian scenes, and all overseen by the astronomer Eustachio Manfredi for accuracy, Creti's painting is the first known to depict the GRS as red. Worth noting is the fact that no Jovian feature was officially described as red before the late 1800s.

On February 25, 1979, when the Voyager 1 spacecraft was 9.2 million km (5.7 million miles) from Jupiter it transmitted the first detailed image of the Great Red Spot back to Earth. Cloud details as small as 160 km (100 miles) across were visible. The colorful, wavy cloud pattern seen to the left (west) of the Red Spot is a region of extraordinarily complex and variable wave motion.

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Wikipedia