Planetary Society Advent Calendar for December 31: Uranus
Did you think I was going to skip Uranus? How could I? I keep coming back to Uranus as one of my favorite places in the solar system, because there's so much to see there, yet it's been so little explored and is quite likely to remain so. Until we visit it again, we do the best with what we have, which is the images from Voyager 2. Björn Jónsson created this view of Uranus using pretty much the same steps as he used to create the view of Neptune that I posted earlier, which means you can put the two pictures next to each other to compare their colors.
NASA / JPL / Björn Jónsson
The images for this color composite of Uranus were obtained by Voyager 2 through orange, green, and blue filters on January 14, 1986 from a range of 12.6 million kilometers. The color has been adjusted to approximate what a human eye would see, although the human eye is sensitive to longer wavelengths of light than the Voyager cameras were. At the time Voyager flew by, little detail was visible in Uranus' atmosphere, though more might have been if Voyager could see into red and infrared wavelengths. Since the flyby, as Uranus has passed through its equinox, it has displayed many more cloud features.
Here's that side-by-side comparison.
NASA / JPL / Bjorn Jonsson
Uranus (left) and Neptune (right)
The images for these two color composites were obtained by the same spacecraft through the same sets of filters and processed in the same way, so should accurately represent the relative colors of Uranus and Neptune at the times that Voyager 2 passed by them.
Really, they are very, very similar. We don't have one blue-green world and one blue one, as the two are so often depicted. They're pretty much the same methane blue; Uranus just had more high haze, making it whiter (not greener) than Neptune. Now that the Uranian equinox is past and atmospheric circulation is producing storms I'll bet they'd look even more similar from up close.
Uranus is not quite the end of my calendar series; there'll be one final post tomorrow. Happy New Year to all!