This month . . . Jupiter’s Great Red Spot.
The most powerful storm in the solar system, so large Earth can fit inside it, still baffles astronomers today. The image above is an enhanced-color image of Jupiter’s Great Red Spot was created by citizen scientist Jason Major using data from the JunoCam imager on NASA’s Juno spacecraft. Courtesy NASA.
It is not known how long Jupiter has had its Great Red Spot. The Italian astronomer Giovanni Cassini is credited with the first observation in 1665.
The Great Red Spot is shrinking. In 1979 the Voyager spacecraft measured its width at 25,000 kilometres but it has now decreased to 15,000 kilometres. The shrinking is not continuous. It went through a period of rapid reduction in 2012 – 2014 but has now appeared to stabilise.
The Great Red Spot is an anticyclone, meaning the winds circulate anticlockwise to that of a cyclone or hurricane on Earth, with speeds between 430 – 680 kilometres per hour. By comparison a Category 5 hurricane on Earth (the highest possible) has speeds of around 251 kilometres per hour.
The Great Red Spot always remains the same distance from the equator at around 20 degrees. Intense jet streams trap the storm preventing it from moving into the north and south hemispheres.
The Great Red Spot hasn’t always been red. It has gone through a variety of colours since its first recorded observations, changing between salmon pink to violet tones until its deep red colour settled in during the early 1880’’s. Its colours are changing again as the storm decreases and are now fading to orange.