Why Is Uranus So Blue?
published during a waning crescent moon.



Credit: Keck Observatory

Uranus must feel a little left out. It’s is so far from the sun, one orbit around our toasty orb is as long as a hearty human life. Despite its distance, Uranus shines on with its blushing blues and greens, hoping to be noticed.

After what must have felt like eons, someone finally did in the 18th century. An astronomer named William Herschel first saw Uranus in 1781 — the first planet to be found using a telescope. (He even made it himself.)

Since then, astronomers have figured out Uranus’ beauty secret. The main ingredient: methane.


Credit: NASA/JPL-Caltech

Uranus is an ice giant, meaning it’s made up of a slush of heavier elements. More than 80% of its mass is a chilly mix of water, methane, and ammonia. It’s the coldest planet in our solar system, even though it’s not the farthest, because its core has no heat source, according to NASA.

Like its neighbors Jupiter and Saturn, Uranus’ atmosphere mostly swirls with hydrogen and helium. But it’s the small amount of cold methane gas in Uranus’ clouds that gives the glowing planet its bucolic colors.

When sunlight floods Uranus’ atmosphere, the methane absorbs the red end of the light spectrum. The cloud tops also reflect some of that sunlight back, which is likely to be on the other end of the spectrum — and that includes those blues and greens that illuminate Earth, too.

And so Uranus floats on its 84-year journey around the, a testament that celestial beauty isn’t limited to what we’re accustomed to back home.