Look up at the sky on a clear day, and the sun appears to be a brilliant yellow orb. This perception is so ingrained that children often color the sun yellow. However, this common belief is actually an optical illusion created by Earth’s atmosphere. In reality, the sun isn’t yellow; its true color is white.
The Sun’s Actual Color: White Light
From space, or to an observer without Earth’s atmosphere interfering, the sun would appear pure white. This is because the sun emits light across the entire visible spectrum, meaning it produces all the colors of the rainbow—red, orange, yellow, green, blue, indigo, and violet—in roughly equal proportions. When all these colors combine, the result is white light. Think of it like a prism: when white light passes through it, it separates into its constituent colors. Conversely, if you were to combine all those colors, you’d get white light again.
Why It Appears Yellow from Earth: Atmospheric Scattering
So, if the sun is white, why do we see it as yellow? The answer lies in a phenomenon called atmospheric scattering, specifically Rayleigh scattering. Earth’s atmosphere is composed of various gases, primarily nitrogen and oxygen molecules. These tiny molecules are more effective at scattering shorter-wavelength light (like blue and violet) than longer-wavelength light (like red and yellow).
When sunlight enters our atmosphere, the blue and violet light waves are scattered in all directions, which is precisely why the sky appears blue. As this blue light is dispersed, the remaining light that reaches our eyes directly from the sun has a higher proportion of longer wavelengths, making it appear more yellow or even orange, especially when the sun is lower in the sky during sunrise or sunset. At these times, the sunlight has to travel through a greater amount of atmosphere, leading to even more blue light scattering and intensifying the yellow, orange, and red hues we observe.
The Concept of Blackbody Radiation
The sun’s emission of light across the entire spectrum can be understood through the concept of blackbody radiation. A “blackbody” is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. While no object is a perfect blackbody, stars like our sun behave very similarly.
The spectrum of light emitted by a blackbody depends solely on its temperature. Hotter objects emit light at shorter wavelengths (more blue), and cooler objects emit at longer wavelengths (more red). The sun, with a surface temperature of around 5,778 Kelvin (9,940 degrees Fahrenheit or 5,505 degrees Celsius), emits its peak radiation in the greenish-blue part of the spectrum. However, as mentioned earlier, it emits so much light across all visible wavelengths that the overall effect is white light. The “yellow” we perceive is merely an artifact of our planet’s protective, yet color-shifting, atmosphere.
