Professor Irwin and his team found that both planets are in fact a similar shade of greenish blue, despite the commonly-held belief that Neptune is a deep azure and Uranus has a pale cyan appearance.
However, astronomers have long known that most modern images of the two planets do not accurately reflect their true colours. The misconception arose because images captured of both planets during the 20th century – including by NASA’s Voyager 2 mission, the only spacecraft to fly past these worlds – recorded images in separate colours.
The single-colour images were later recombined to create composite colour images, which were not always accurately balanced to achieve a “true” colour image, and – particularly in the case of Neptune – were often made “too blue”. In addition, the early Neptune images from Voyager 2 were strongly contrast enhanced to better reveal the clouds, bands, and winds that shape our modern perspective of Neptune.
Read More: University of Oxford
Voyager 2/ISS images of Uranus and Neptune released shortly after the Voyager 2 flybys in 1986 and 1989, respectively, compared with a reprocessing of the individual filter images in this study to determine the best estimate of the true colours of these planets. (Photo Credit: Patrick Irwin, University of Oxford)