Over a period of seven months in 2017, the Hubble Space Telescope photographed a beautiful display of northern lights over Saturn’s north pole.

Earth’s northern and southern auroras happen when the planet’s magnetic field interacts with the solar wind, the stream of charged particles streaming from the sun. They are visible to the naked eye. Unlike Earth, Saturn has an atmosphere composed mostly of hydrogen, which produces ultraviolet lights when interacting with particles in the solar wind.

The human eye can’t pick up that ultraviolet light, and most of it would be absorbed by Earth’s atmosphere anyway. Such lights cannot be seen by the naked eye or ground-based telescopes but can be captured by the Hubble from space.

Saturn in ultraviolet. (ESA/Hubble, NASA & L. Lamy (Observatoire de Paris))

Hubble’s observations revealed an ever-changing aurora on Saturn’s north pole that varies as the solar wind ebbs and flows and as the planet rotates. (A full Saturn rotation takes just 11 hours.) The aurora peaked in brightness at the planet’s dawn and just before midnight, researchers said in the statement — but that midnight peak, never seen before, might have something to do with the way the solar wind hits the planet around the solstice, in particular.

“The variability of the auroras is influenced by both the solar wind and the rapid rotation of Saturn, which lasts only about 11 hours,”

“On top of this, the northern aurora displays two distinct peaks in brightness — at dawn and just before midnight. The latter peak, unreported before, seems specific to the interaction of the solar wind with the magnetosphere at Saturn’s solstice.”

ESA writes.

Though Saturn’s auroras have been photographed before by Hubble, these new images reveal the auroras peaking in brightness around dawn and just before midnight.

While Earth’s auroras stretch upward around 100 to 500 km into the atmosphere, Saturn’s auroras can reach heights of more than 1,200 km.