Why does Uranus look blue?
Uranus looks blue-green because methane gas in its upper atmosphere absorbs red light from the Sun and reflects blue and green light back into space.
Uranus's atmosphere is mostly hydrogen and helium, with about 2 percent methane. Sunlight passes through the atmosphere and bounces off clouds below. Methane absorbs the red part of the light, so mostly blue and green light is reflected, giving Uranus its pale cyan color.
Neptune also contains methane and was long shown as a deep blue, while Uranus looked paler. A 2024 study reprocessed old Voyager 2 images and found that the two planets are actually much closer in color than many pictures suggested, both a similar greenish-blue, with Neptune only slightly bluer.
A haze effect
Uranus appears paler partly because it has a thicker layer of haze in its atmosphere, which whitens its color. Uranus's color also changes slightly over its long 84-year orbit, as its unusual tilt changes how much of each pole faces the Sun.
Did You Know?
Uranus is the coldest planet in the solar system, with temperatures in its atmosphere falling to about minus 224 degrees Celsius.