The red hues of sunrise at the dawn, the golden white shimmer towards the noon or the brilliant tangerine winter sunset over a snowy field, the Sun never ceases to awe us with its display of colours!? When asked about the colour of sunlight, a reflexive response would be, ‘yellow’ or ‘white’! You might also answer ‘red’ or ‘orange’ if ‘dawn and dusk’ pop up in your mind. Nevertheless, what colour is the sunlight actually?
Sunlight: A Mixture of Colours
Let us demonstrate the colours of sunlight through a small activity.
- We take a glass tumbler or a transparent bowl full of water.
- We place it in a position such that direct sunlight falls on it through the window.
- We fix the white paper on the floor as shown in the figure such that the rays of sun passing through the glass tumbler falls on the sheet.
We observe on the paper that the sunlight is split into a spectrum of colours like a rainbow, every colour in VIBGYOR i.e., violet, indigo, blue, green, yellow, orange and red can be seen. The conclusion drawn here is that sunlight is nothing but a mixture of seven colours. And these seven colours combine to form the white light.
Why does the sunlight appear red, orange or yellow?
When the sun rays enter the earth, they get distorted by the earth’s atmosphere including air molecules, dust and smoke. We know that different colours of the spectrum have different wavelengths. The short-wavelength blue and violet are scattered more than colours of the lower end of the spectrum which are less easily scattered.
If the sun is overhead in the sky, the rays suffer the least amount of interference because the distance covered by them is the least at that point in time. Consequently, the blue light is scattered and the sky appears blue whereas the rays of the sun appear yellow.
Morning and Evening
During the sunrise and sunset, the sun is near the horizon due to which the light rays have to travel a longer distance through the atmosphere. As a result, there is more interference which causes more scattering of light. Consequently, most of the colours, including the blue as well as the yellow are scattered leaving the red light. Hence, the sunlight appears orange and red during dawn and dusk.