Why is the colour of clear sky blue ?

When sunlight enters the earth’s atmosphere, the atoms or molecules of the gases present in the atmosphere scatter this light. Since wavelength

of red colour is larger than the wavelengths of other colours in sunlight, so red colour is scattered least. Violet colour is scattered the most

followed by blue, green, yellow, orange and red colours respectively. Our eye is more sensitive to the blue light than the violet light. Therefore,

scattered light in the sky contains blue colour in plenty and hence the clear sky appears blue.

Note : Sky appears greyish over cities having industrial units. The smoke and dust particles in the atmosphere over such cities scatter red, orange

and yellow colours more than other colours of small wavelengths. Hence, the sky appears greyish.