Colour of the Sun at Sunrise and Sunset: Sunlight, Dispersion of Light and VIBGYOR

Ever wondered why the colour of sun changes with red hues of sunrise at dawn, the golden white shimmer towards noon or the brilliant tangerine winter sunset over a snowy field. But does sun have a constant colour? The probable answers are red, yellow, orange, but these all are wrong answers the sun which is the centre of our solar system is White in colour. It is the atmosphere of Earth which makes the sun to appear in the various colours like red, yellow, orange.

Read Also: Light-Reflection and Refraction Revision Notes

What is sunlight?

[Click Here for Sample Questions]

The white sunlight is a mixture of seven colours which are violet, indigo, blue, green, yellow, orange and red popularly known as VIBGYOR. In the VIBGYOR the Red light has the highest wavelength and violet the lowest wavelength. When white light is passed through a prism the different wavelengths and gets splatted in to the various components colours as shown above.

Interference is the phenomenon in which two or more waves superpose to form a resultant wave which has greater, lower, or the same amplitude of the component waves.

The video below explains this:

Human Eye One Shot Detailed Video Explanation:

Why do we see different Colors at sunset and sunrise?

[Click Here for Sample Questions]

The atmosphere of earth is composed of various different gases and vapours like oxygen, nitrogen, water vapor and carbon dioxide. In addition to these gases and vapours, there are also various other impurities like dust, smoke particles, and polluting gases like methane and CFCs. When the sun rays from space strike the earth’s atmosphere to pass through it, they get distorted by the earth’s atmosphere due to the presence of all these materials in the earth’s atmosphere. Different colours present in the spectrum have different wavelengths.

The wavelength of a material is defined as the distance between two successive crests (highs) or two successive troughs (lows) of a wave. So, the longer is the wavelength, the lower is the frequency. Thus, due to their short wavelengths, blue and violet are scattered more. Conversely, colours of the other end of the spectrum do not get scattered as much, as they consist of longer wavelengths. As a result of which there are different colours of the sun observed at sunrise and sunset.

The difference in color is discussed below: -

• During sunrise, the sun is at its farthest distance from the horizon of earth, and seems to be rising from the horizon. As a result of this, the light rays have to travel a much longer distance through the earth’s atmosphere. Therefore, they are obviously subjected to more interference, resulting in an increased amount of scattering of light. Consequently, out of all the colours, the red light gets least scattered. The same phenomenon also occurs during sunset when the sun is seemingly moving towards the horizon, and as a result, the sunlight colour appears to be of varying shades of red and orange during the dawn and dusk.
• When the sun is directly over us during late morning and noon, the sun’s rays are subjected to the least amount of interference because of the distance traversed by the rays is the least at that time. Therefore, during this time interval, blue light gets the most scattered, and the sky appears to be blue, while the sun’s rays appear to be yellow.

Read More Tyndall Effect