Imagine gazing up at the night sky and spotting a brilliant emerald star twinkling among the familiar reds, yellows, and blues. Yet despite the universe’s vast stellar palette, this particular hue remains mysteriously absent from our cosmic canvas. Scientists have long puzzled over this celestial color gap, and the answer reveals a fascinating conspiracy between physics and biology.
Why green stars remain invisible despite favorable atmospheric conditions
They all emit their light through thermal radiation over all parts of the electromagnetic spectrum, meaning they all have black body emission that is continuous and can never be of pure green color. Actually, our sun has its maximum emission of around 550 nanometers, but this is perceived as bright white light and not green light at all.
Wien’s displacement law indicates that a star with a surface temperature of about 5,800 Kelvin would be green in color, theoretically. But due to the laws of thermal radiation, such a star actually emits equal quantities of red and blue light simultaneously. So, a star can never be green, irrespective of its point of emission on the electromagnetic spectrum.
The shocking truth about our sun’s real color
Our Sun is actually green. It shines brightest at about 500-550 nanometers, and this falls squarely inside the green region of the color spectrum. But we never actually see a green color because of black body emission, and because our eyes are attuned to interpret a range of lights as white light.
Human vision creates the cosmic color illusion
Our eyes have three types of cone cells that respond maximally to light of different wavelengths:
- Red cones – sensitive to longer wavelengths (about 560-700nm)
- Green cones – sensitive to middle wavelengths (about 530-560nm)
- Blue cones – respond to shorter wavelengths (about 420-490 nm
These photo-receptors neither identify the maximum wavelength nor identify the ratios of intensity of all channels. If starlight showers our eyes with a mix of all wavelengths, our brain perceives this mix as white and not green. Dr. Alastair Gunn says, “If a star emits maximum light of a certain wavelength, say ‘green,’ it actually emits almost as much ‘red’ light, and our eyes perceive this mix as ‘white’ and not ‘green’.”
Color vision requires isolation of green wavelengths
Real green substances get their color because of selective methods, not because of thermal radiation. Plant color is due to chlorophyll absorbing red and blue parts of light and radiating green, while auroral displays produce green because of oxygen atoms emitting a narrow band of radiation of wavelength 557.7 nanometers, resulting in a single wavelength that is green.
The universe follows strict thermal color rules
Stellar colors progress predictably based on surface temperature:
- Cool red stars (3,000K) – peak in infrared, appear red
- Orange stars (4,000K) – balanced red-yellow emission
- Yellow stars (5,000K) – broad spectrum, appear yellow-white
- White stars (6,000K) – peak in green, appear white
- Blue stars (10,000K+) – peak in blue, appear blue-white
No temperature range can enable wavelength isolation sufficient for green perception. Even some bizarre stellar matter composition, having some weird elemental emission, cannot compete successfully with the omnipresent blackbody radiation.
“But for our eyes to see it as green, a star would have to emit only green light, which is not possible.” – Dr. Alastair Gunn, University of Manchester
The fact that we don’t have green stars has ultimately got a lot to do not only with the physical principles of thermal radiation but also with evolution itself, as our eyes have adjusted to our sun, which shines green but looks white due to its broad spectrum of colors. It is just a coincidence that we can see our star as white and not be able to see any other green, regardless of its actual color.
