Great Red Spot
- Huge reddish oval storm structure, 14,000 by 30,000km, which has been observed in the atmosphere of Jupiter since telescopes were first turned on it in the 17th century. The Spot is an anticyclone whose boundary with the rest of the Jovian atmosphere is the site of immense activity, with other spots being swept past the Spot and sometimes merging with it. For the last 40 years three companion white spots have also been visible near the Great Red Spot. Numerous theoretical models exist of possible structures for the Great Red Spot, although the need to account for its longevity is a severe constraint on possible explanations.