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Uranus has always been regarded as a difficult target for observation by amateur astronomers. It is certainly not difficult to find but it is very distant and hence dim, often below the limit for naked-eye observation in the UK and barely showing a disc through even powerful binoculars. Telescopically it also appears bland at the eyepiece, a pale green coloured disc with no obvious features to allow observers to pick out banding in the atmosphere, though dedicated observers report having seen glimpses of such features in larger instruments. Photographically the story is somewhat different.
Modern monochrome planetary cameras, developed from web-cam technology to capture streams of video images and using filters that pass infra-red light to the camera sensor, have, in the hands of amateur observers, caught distinct shading and banding features in the atmosphere of the planet; now there is a new target to try and capture.
Planetary Science researchers using one of the largest telescopes available on Earth have captured images of major storm features rotating in the higher northern latitudes of Uranus.
The instrument used to capture these images, taken in August, was the NIRC2 near-infra-red camera using adaptive optics mounted on the 10 m Keck II telescope, situated on the dormant volcano ‘Mauna Kea’ on the island of Hawaii. When Voyager passed by Uranus in 1986 it photographed only a few light patches and streaks of cloud in the upper atmosphere but currently there are multiple cloud areas visible including one monstrous storm, all in the Northern Hemisphere of the planet. Uranus had its solar equinox in 2007 when available sunlight fell equally on the Northern and Southern Hemispheres. Since then the planet has been moving firmly into its northern summer and the South Pole is no longer visible to us from Earth. Prior to the equinox other large storms had been glimpsed in the deep south with one large one in particular being known as ‘The Berg’ since it resembled a massive iceberg floating away from the South Polar region. The current monster storm seems to be bigger and brighter than The Berg.
These professional images were taken in the infra-red at 1600 angstrom (1.6 micron) frequency but amateur imagers have recently caught the atmospheric banding using filters that pass deep-red light into the near infra-red. Given the size of the storm features observers equipped with larger aperture telescopes, of perhaps 10 inch (250 mm) or more, have a chance of capturing images of these features and using them to examine the speed of the jetstreams flowing in the upper atmosphere of Uranus. With Uranus reaching opposition on the 7th of October this year it will soon be observable all night long against the background stars of Pisces and imaging these storms is a difficult but worthwhile challenge for the amateur observer.
Added by: Alan Clitherow