Fact Sheet
The Other Blue Planet
Cirrus clouds float atop the thick blue atmosphere of Neptune, the fourth-largest planet in the solar system, in this 1989 image from Voyager 2. Methane in its atmosphere reflects blue wavelengths of sunlight and absorbs other colors, giving the planet its deep color. Neptune is at its brightest in Earth's night sky this week, although it is visible only through telescopes.
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