Qualla: Great Red Spot

Great Red Spot: Introduction

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Michael Benson / Tycho Henderson at en.wikipedia, CC BY 1.0. On September 5, 1831, an astronomer pointed a telescope at Jupiter and saw a red oval south of the equator. He was not the first to see it. Robert Hooke described a Jovian spot in 1664, and Giovanni Cassini calculated its rotation period in the following year. But those earlier spots may or may not be the same storm. A 2024 analysis suggests they were not. What the 1831 observer saw, though, has been watched continuously ever since. Every night the planet is visible, somewhere in the world an astronomer is looking at it, and the Great Red Spot is still there, still turning, still rising eight kilometers above the surrounding cloud deck.

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Image: Michael Benson / Tycho Henderson at en.wikipedia | CC BY 1.0

Great Red Spot: A Storm Bigger Than a Planet

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Donato Creti, Public domain. As of April 2017, the Great Red Spot measured 16,350 kilometers across, about 1.3 times the diameter of Earth. It has been shrinking for a century, and as of the most recent measurements, it is now slightly smaller than our planet but still easily the largest storm in the solar s...

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Image: Donato Creti | Public domain

Great Red Spot: Why It Does Not Stop

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Justin Cowart, Public domain. On Earth, hurricanes die when they hit land. Friction breaks up the circulation, the storm loses its fuel, and within days the winds dissipate. Jupiter has no land. The planet is a gas giant whose outer atmosphere of hydrogen merges smoothly into a hydrogen mantle below, and ther...

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Image: Justin Cowart | Public domain

Great Red Spot: Red Spot Hollow and the Color Question

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Kevin M. Gill, CC BY 2.0. The color varies. Sometimes it is brick red. Sometimes pale salmon. Sometimes it fades so much that the only evidence of the spot is the Red Spot Hollow, a darker indentation in the South Equatorial Belt where the storm resides. When the belt goes bright white, the spot tends to ...

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Image: Kevin M. Gill | CC BY 2.0

Great Red Spot: The Flaking Years

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Kevin M. Gill, CC BY 2.0. In 2019, amateur astronomers noticed something new. Pieces of the spot were spinning off. Red fragments broke away from the edges and dissipated into the surrounding atmosphere. The shrinking had been going on for a century, but the flaking was new, and some astronomers speculate...

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Image: Kevin M. Gill | CC BY 2.0

Great Red Spot: What Juno Saw

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Kevin Gill from Los Angeles, CA, United States, CC BY-SA 2.0. On July 11, 2017, NASA's Juno spacecraft flew over the Great Red Spot at a distance of about 5,000 miles above the cloud-tops. The images were the closest ever taken. Gravity measurements during Juno's overflight showed that the spot extends downward into the planet at least 200 ...

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Image: Kevin Gill from Los Angeles, CA, United States | CC BY-SA 2.0

Great Red Spot: Note on Location

Thu, 16 Apr 2026 00:00:00 GMT

Photo credit Kevin M. Gill, Public domain. This article is filed in the catalog at coordinates for central South America, which is an indexing error. The Great Red Spot is on Jupiter. It is an anticyclonic storm at 22 degrees south on the fifth planet from the sun, 778 million kilometers from Earth on average, visible to ...

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Image: Kevin M. Gill | Public domain