Blue light has a shorter wavelength, while red light has longer wavelengths.
As sunlight covers longer distances, the shorter-wavelength blue light scatters more, allowing the longer-wavelength yellow and red light to become more visible.
The Sun, a fiery sphere, radiates intense brightness, often dazzling our eyes. Nonetheless, during sunrise and sunset, it transforms, appearing red, followed by an orange and purple sky. Exploring the science behind this phenomenon, we delve into why the Sun exhibits these colours.
First, let’s explore how we perceive colour. Sunlight travels from the Sun through the atmosphere in the form of invisible waves. What we commonly see as white light is, in fact, a mixture of different colours, each defined by its specific wavelength. For example, blue light has a shorter wavelength, while red light has longer wavelengths.
The shift in the sun’s colour at sunrise and sunset is attributed to Rayleigh scattering, a concept introduced by British physicist Lord Rayleigh in the 19th century, as reported by the BBC. As sunlight covers longer distances, the shorter-wavelength blue light scatters more, allowing the longer-wavelength yellow and red light to become more visible. This phenomenon is known as Rayleigh Scattering.
Rayleigh scattering clarifies how sunlight, as it enters the Earth’s atmosphere after leaving the Sun, interacts with atmospheric dust particles, leading to the dispersion of light.
This scattered sunlight contains a spectrum of colours, such as red, orange, yellow, green, blue, dark blue, and violet, all perceptible to the human eye. Each colour is associated with a specific wavelength, with violet having the shortest wavelength and red having the longest.
Sunlight scatters when it encounters gases in different air layers, altering its path and sometimes dividing into distinct components. Particles reflect some of this light. During sunrise or sunset, the Sun’s rays hit the uppermost atmospheric layer at specific angles, triggering an intriguing process.
Here, the Sun’s rays split into blue wavelengths, which are reflected rather than absorbed. When temperatures drop, blue and green wavelengths scatter, while violet and blue rays, due to their shorter wavelengths, become less visible. In contrast, orange and red wavelengths, with their longer wavelengths, become more prominent in our eyes.
In simple terms, during sunrise and sunset, the Sun appears red because the majority of the blue light in sunlight scatters out of our line of sight, leaving primarily red light in the direct sunlight that we see.
