Uranus is known to have a calm weather, but it appears that the planet has suddenly woke up from its long slumber as astronomers have observed intense storms on the normally placid icy giant.

Imke de Pater, an astronomer from the University of California, Berkeley, and colleagues first detected unusual bright cloud activity on the planet's upper atmosphere using the telescopes at the Keck Observatory in Hawaii.

Over a period of just two days from Aug. 5 to 6 earlier this year, the scientists found eight storms on the northern hemisphere of Uranus, the seventh planet from the sun that is mostly made up of ices.

One particular storm is the brightest to be ever seen on the planet accounting for 30 percent of all reflected light coming from it at 2.2 microns, which offers information about clouds below the tropopause, the lower boundary of the stratosphere where the pressure is half of that in the Earth's surface.

The phenomenon has puzzled astronomers as this should have happened seven years ago when the sun shone directly on the planet's equator and supposedly produced more heat and stormy weather.

"This type of activity would have been expected in 2007, when Uranus's once-every-42-year equinox occurred and the sun shined directly on the equator," said Heidi Hammel, a planetary astronomer with the Association of Universities for Research in Astronomy who was part of the team that first noticed the abnormal weather activities on Uranus. "But we predicted that such activity would have died down by now. Why we see these incredible storms now is beyond anybody's guess."

Amateur astronomers, who have heard about the unusual storms, also used their own telescopes to observe the planet and regardless that the instruments they used were smaller compared with those used by professional scientists, they were able to see an unusual bright spot on the planet's atmosphere.

Notably though, the bright storm that de Pater and colleagues have seen using Keck II telescope is not the same one that the amateur astronomers have seen as the bright spot they saw is much deeper in the atmosphere.

Planetary scientist Larry Sromovsky, from the University of Wisconsin, Madison, said that the bright light detected by the amateur astronomers was also featured in the Aug. 5 images from the Keck Observatory but it was seen at 1.6 microns.

"These unexpected observations remind us keenly of how little we understand about atmospheric dynamics in outer planet atmospheres," the researchers said.