The outer solar system is playing host to some really big storms at the moment, giving astronomers an unusual insight into the atmospheres of the gas giants.
On Saturn, a huge hexagonal hurricane larger than the Earth itself has appeared at the North Pole.
New York Times
However, the storms are even more interesting at Uranus. The Earth has seasons because the axis around which we spin does not point at right angles to the plane in which we travel around the sun. Instead it tilts, and the hemisphere tilted towards the sun gets more light than that tilted away. Things are pretty similar on most of the other planets. Saturn's axial tilt, for example is 26.7° as compared to our own 23.5°. Venus and Jupiter hardly have seasons at all, with tilts of just 3°.
But Uranus has an axis that runs almost parallel to the plane of its orbit; 82° away from sticking straight up. While it never gets warm on Uranus the seasons are intense, with long periods where the sun is almost directly over one pole, leaving most of the other hemisphere in a seriously cold night that lasts for years. The polls actually receive more light than the equator, although for reasons unknown, the equator is on average warmer.
However, just to make things more complex when you add the fact that Uranus spins backwards, compared to the other planets, making its tilt 98°, rather than 82.
This might be expected to create some pretty amazing weather systems, but when Voyager 2 went by in 1986 nothing much seemed to be happening.
However, as telescope technology has improved we've started noticing storms, suggesting Voyager just had bad timing. The north pole of Uranus is also starting to point towards the sun and this has been accompanied by images of huge storms. “Even after years of observing, a new picture of Uranus from Keck Observatory can stop me in my tracks and make me say Wow!,” said observing team member Dr Heidi Hammel.
Imke de Pater (UC Berkeley) / Keck Observatory
It is thought the bright spots in the image above are methane ice thrown into the upper atmosphere by tempests. An almost equally bright storm was seen in Uranus' southern hemisphere around the 2007 equinox.
At his blog Bad Astronomy, Phil Plait reports that if amateur astronomers can detect these storms precious time on the Hubble telescope will be devoted to photographing Uranus. So any amateurs with decent sized telescopes, here is your chance to influence the course of science. Not to mention winning a license to make the same tired joke for the rest of your life. For everyone else who just wants to know what the fuss is about, the best time to find Uranus in the sky is probably on Thursday night, when it will be 1.5° away from the moon, although the lunar brightness may drown it out a bit.
2