Look up at the night sky. The stars first appear white, however, a closer look reveals many different colors. The night sky is filled with glittering jewels. Except for green. Here’s why …
The Colors of Stars
Some stars clearly look yellow, white, orange, or blue. Binoculars gloriously bring out these pastel hues. A small telescope reveals red and even purple. Blacks and browns are out there, too.
But no green! That’s ironic, because green is the color to which our eyes are most sensitive.
The Sagittarius Star Cloud. Note: In real life, to the eye, reds are rarely as deep as seen here. Blue, yellow, and orange are more common. Credit: NASA
For a quick demonstration of our emerald-tinted vision, look around when twilight deepens. As your vision slowly adjusts, all hues fade out until the last to vanish is … green. By the full Moon, your lawn will still look dimly green when garden roses and violets have all become gray.
This human sensitivity to green is why, in the 1950s, they decided to use that color for the signs in the Interstate Highway System. It also explains why more and more municipalities are replacing their traditional red fire trucks with pale green ones. (Despite this, surveys show that blue is most often named when people are asked their favorite color.)
Why no green stars? Our star (the Sun) and most stars actually do give off green light but also the stars give off enough blue and red light that our eyes end up perceiving many colors at once, so we see it as white. In other words, when such mixtures are involved, so far as our vision goes, the sensation of white is what we see instead of green.
The Colors of Other Celestial Objects
When it comes to the solar system, many planets have no obvious tint. With Venus, Saturn, and Jupiter it’s a case of the bland leading the bland. They seem whitish to the naked eye.
But a few planets do boast decisive color: Neptune looks blue, Mars orange, and Uranus—that’s the cosmic Erin. Its green is obvious through any telescope.
Uranus gets its blue-green color from methane gas in the atmosphere. Credit: NASA
Brilliant meteors, too, sometimes display a vivid green that can appear as in-your-face as a traffic light.
And bright auroras, if you’re lucky enough to see one. Green is far and away the most common color of the Northern Lights.
Just not stars.
Credit: Anjali Bermain from the Northern Lights Tour With The Old Farmer’s Almanac!