What Causes The Sun to Turn Red in The Mornings

The sunrise or sunset of the Sun offers a spectacle that is often overlooked.  If we stop to look carefully at what we´re witnessing during a sunrise, we may notice that the horizon presents various color changes as it raises high in the sky. These colors go from reddish, to an orange and to a yellow tone.

The diffraction of light in the atmosphere is most commonly caused by an optical phenomenon known as the Rayleigh scattering. The Rayleigh scattering of light causes the skies to turn blue during daytime and the red or orange color of the Sun at sunrise and sunset. Portions of the light spectrum are scattered more than others, depending on the frequency and wavelength of light.

When these portions of light encounter the particles (pollution) and molecules in the atmosphere, they collide against these particles and get diffracted out in the sky; however, the higher frequencies are diffracted more than the lower frequencies. Violet and blue light which have wavelengths of 380-450 and 450-475 nanometers respectively are most diffracted than red, orange and yellow which have wavelengths of 620-750, 590-620 and 570-590 nanometers respectively.

The Earth´s atmosphere scatters light proportional to the fourth power of light wavelength. Shorter wavelengths, such as blue and violet, are deviated out into the sky more than longer wavelengths, such as red, orange and yellow. That´s the main reason that the sky appears blue at noon. Green and red acquire a yellowish tone when they get mixed, creating the characteristic yellow tinge of the Sun at noon.

At dawn, the Sun appears of a reddish hue in the horizon; however, the sunlight has to go through a higher amount of atmospheric particles and molecules before it reaches our eyes in the early morning than at noon due to the greater angle at which the Sun is with respect to Earth. At dawn, sunlight has to travel a longer distance in the atmosphere, therefore, shorter frequency light, such as blue is scattered into the surrounding sky; however, shorter wavelengths are able to pass through the atmosphere and reach your eyes.

The reddish and then orange hues of the morning Sun are characteristics of the scattering of light. As the Sun continues rising in the sky, it acquires different nuances, including red just before rising followed by orange and so on according to the colors of the light spectrum. It´s important to note that as the Sun rises higher in the sky, sunlight travels smaller distances, allowing higher frequencies to go through the atmosphere without being deviated, resulting in blue skies.