In late 2010, an amateur astronomer noticed an odd white spot in Saturn's northern hemisphere. It was a storm, like a gigantic hurricane, which quickly grew in size to thousands of kilometers across and rapidly surpassed the diameter of our own planet. And yet it continued to grow, and in February 2011 the Cassini spacecraft orbiting Saturn took this incredible picture showing the storm had grown so long it had literally wrapped its way around the entire planet! At this point, it was a staggering 300,000 km (180,000 miles) in length - the same distance as 3/4 of the way from the Earth to the Moon!

Pictures taken in late 2010 and early January also show details of the storm in psychedelic false color, where the whorls and vortices of the raging weather are clear. Saturn's face is usually far more subtle and calm than this - look at the nice, smooth southern hemisphere for comparison - so the eruption of this storm was a surprise to astronomers... but surprises are good, because in many cases that's how we learn things. And I'm glad Cassini was there to get these amazing close-up shots.

Image credit: NASA/JPL-Caltech/SSI

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