Why is sunset more reddish than sunrise?

Why is sunset more reddish than sunrise?

Neerad Tanvi, Bikaner

The light from the Sun travels through Earth’s atmosphere it undergoes scattering before it reaches us. The extent of scattering is not uniform for all colours. Light of shorter wavelengths, such as violet, blue, green and yellow undergoes greater scattering than those of longer wavelengths, such as orange and red. Because of the spherical geometry of the earth, the sunlight travels longer distance in the thick of the earth’s atmosphere during sunset and sunrise when the Sun is at the horizons than when the Sun is at the zenith (midday). Thus, there is more probability for shorter wavelength light to get more scattered than for the longer wavelength light. Hence, the Sun (and sunrise and sunset) appears reddish orange during sunset and sunrise.

The scattering is also related to the size and quantity of the scattering particles. During the night time the atmosphere is cool and the aerial particles and dust particles settle by morning whereas by evening they get dispersed. Thus, the scattering is more by evening than in the morning.

Lastly, since the earth is spinning from West to East, relatively we move towards the Sun during mornings (eastward) and away from the Sun during evenings (westward). There is one phenomenon, called, Doppler Effect, which adds to this differential.

In other words, there is an inherent natural cause forthis differnce between morning and evening sunlight.

Prof. A. Ramachandraiah

NIT, Warangal

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