The common understanding that the Sun is yellow or orange is a visual trick played by Earth’s atmosphere, leading to a long-standing misconception. Scientifically, the light emitted by our star before it passes through any gas or haze is not yellow. When viewed from the vacuum of space or high in the atmosphere, the Sun appears strikingly white. This difference between the Sun’s true and perceived color is explained by the physics of light, the properties of our star, and the limitations of human vision.
Defining the Sun’s Hue
The true color of the Sun is determined by its surface temperature, approximately 5,778 Kelvin (K), and its classification as a G2V star. Objects heated to incandescence, like stars, emit light following blackbody radiation, where the peak wavelength of light emission is directly related to the object’s temperature. The Sun’s temperature causes its light emission to peak near the green-blue portion of the visible spectrum, around 500 nanometers.
The Sun radiates across the entire visible spectrum, from violet to red, not just at this peak wavelength. Because the Sun emits all these visible colors in nearly equal intensity, the combined light appears white to the human eye. Although the peak emission is slightly greenish, the full spectral output averages out to white light. Astronomers classify the Sun as a “yellow dwarf” (G2V) due to historical convention, not because its visual appearance is yellow.
The Atmospheric Illusion
The reason the Sun appears yellow or orange from Earth’s surface is due to a phenomenon called Rayleigh scattering, which is the scattering of light by air molecules. Earth’s atmosphere is composed primarily of nitrogen and oxygen molecules, which are much smaller than the wavelength of visible light. These small molecules are far more effective at scattering shorter, higher-energy wavelengths of light, such as blue and violet, than longer wavelengths like red and orange.
As white sunlight enters the atmosphere, the blue and violet light is scattered in all directions across the sky. This widespread scattering is precisely what makes the sky appear blue during the day. The remaining direct sunlight reaching the observer has had a significant portion of its blue component removed. This subtraction of blue light shifts the color balance of the direct light toward the longer wavelengths, resulting in the perception of a yellow-tinted Sun.
The illusion is amplified during sunrise and sunset, when the Sun is low on the horizon. The light must travel through a much greater thickness of the atmosphere to reach the observer’s eye. This extended path length causes even more of the shorter-wavelength light, including blue and green, to be scattered away. What finally reaches the eye is light dominated by the least-scattered, longest wavelengths, which are red and orange, creating the warm glow of the setting Sun.
How Our Eyes Interpret Brightness
The human visual system also plays a role in how the Sun’s color is interpreted, especially due to its extreme brightness. The light from the Sun is so intense that it saturates the cone cells in the retina, the photoreceptors responsible for color vision. When the light is too bright, the cones are overloaded, and the visual system struggles to process the exact spectral composition, often resulting in a generalized white or near-white perception.
Our brains also employ a cognitive mechanism known as color constancy, which is an unconscious adjustment to lighting conditions. This mechanism ensures that familiar objects retain their perceived color despite changes in the light source. For instance, a white sheet of paper looks white whether viewed under a yellowish incandescent lamp or a bluish fluorescent light.
The brain applies this same principle to the Sun, interpreting the primary light source as a “standard” color. Because of the constant atmospheric scattering that removes the blue light, our visual system learns to normalize the Sun’s color to the yellow-white hue we see daily. This learned normalization reinforces the perception of a yellow Sun, even though the light source itself is physically white.