How about this — I'll tell you a couple of things that it isn't. It's not an iridescent oil slick, and it's not the interference patterns of a soap film. But you knew that already, didn't you? After all, this post is tagged as space porn.
That was your big hint. Answers below!
Alright, so I may have lied a little bit. Technically speaking, this isn't a picture. To be more precise, this is a false-color mosaic — two of them actually, one on top of the other, each one comprising a total of 84 images captured by NASA's Cassini spacecraft earlier this year (click here for the hi-res, "panoramic" version).
These mosaics chronicle the changing appearance of a massive storm that first formed on Saturn's northern hemisphere back 2010, but eventually grew so large it wound up wrapped all the way around the planet.
Each image was taken over the course of about 4.5 hours on February 26th of this year, and the top image was taken about 11 hours before the bottom one. (Other psychedelic mosaics can be found here and here.)
According to the Cassini Imaging Central Lab for Operations (CICLOPS):
This storm is the largest and longest-lasting observed on Saturn by either NASA's Voyager or Cassini spacecraft. The storm's active phase ended in June 2011, but, as of October 2011, the turbulent clouds have continued to linger in the atmosphere. As seen in these and other Cassini images, the storm encircles the planet whose circumference at these latitudes is 186,000 miles (300,000 kilometers). From north to south, it covers a distance of about 9,000 miles (15,000 kilometers), which is one-third of the way around the Earth. It encompasses an area of 2 billion square miles (5 billion square kilometers), or eight times the surface area of Earth. This storm is about 500 times the area of the biggest of the southern hemisphere storms observed by Cassini (see PIA06197).
[Spotted on Bad Astronomy]