It’s a bright, beautiful day, with the lovely green sun shining overhead. Wait, you might say — green? We typically think of the sun as yellow or orange. Yet if we measured all the light our star emits, we’d find it shines most strongly in the green part of the spectrum. This has led some people to claim that the sun is really green.
Confusion over the sun’s color may come from mixing up two things — an object’s apparent hue and the wavelength where its light is strongest. That last feature is known as the light’s peak intensity. These two aren’t always the same.
Peak intensity is the specific point within the broad spectrum of light where the emitted hue is most intense. Color, though, is how our brain interprets the full mix of light wavelengths entering our eyes.
The sun’s peak intensity is at a green wavelength. But green is just one of many colors of light the sun emits. Sunlight spans the whole light spectrum — from long-wavelength radio waves to short-wavelength X-rays. The part we can see makes up a small chunk in the middle. This is known as the visible spectrum.
Within the visible spectrum, the way we perceive light’s color relates to how our eyes work.
Our eyes have three types of cone cells. S cones respond most strongly to blues and other short wavelengths of light. M cones respond most to mid-wavelength light, such as green. Those that respond mostly to reddish hues are the L cones. Our brain processes data coming from all three types of cones to perceive color.
When there’s light coming from all the different colors of the rainbow, we perceive that as white light. And if our eyes could see the whole mix of the sun’s visible wavelengths, it would tend to appear white. So why does the sun generally seem yellow?
That’s “the effect of the Earth’s atmosphere,” explains Kate Dellenbusch. She’s an astronomer at Bowling Green State University in Ohio.
When sunlight hits gas molecules in our atmosphere, they scatter the shorter wavelengths of light. This includes blue and violet ones. Light with longer wavelengths — such as red, yellow and orange — will pass through the atmosphere to reach our eyes. This is why the sky looks blue and the sun looks mostly orange, yellow or red. (The exact hue depends on atmospheric conditions, including cloud cover.)
Atmospheric effects
Sunlight gets deflected by particles in the atmosphere (shown as a blue band above Earth’s surface) through what’s known as Rayleigh scattering. The effect depends on the light’s wavelength. Shorter blue and green wavelengths scatter much more than longer yellow and red hues. This affects what color the sun appears to us.
If we could observe the sun without Earth’s atmosphere, then would it look green?
Still no, says Terry Kucera. She’s a solar physicist — a scientist who studies the sun — at NASA Goddard Space Flight Center in Greenbelt, Md. Our brain doesn’t pick out the sun’s peak intensity from its full spectrum. “Assuming we can take a filter to look at the sun,” she says, “it will look white to us.” This is also how astronauts see the sun from space, outside of Earth’s atmosphere.
Even though our sun produces a significant amount of green light, we’ll never see it that way. We’ll still see a golden, glowing orb.
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