When the Sun is near the horizon during the morning or evening, it appears reddish. The phenomenon that is responsible for this observation is
[amp_mcq option1=”reflection of light” option2=”refraction of light” option3=”dispersion of light” option4=”scattering of light” correct=”option4″]
This question was previously asked in
UPSC CDS-1 – 2018
The phenomenon responsible for the reddish appearance of the Sun near the horizon is scattering of light, specifically Rayleigh scattering. As sunlight passes through a longer path in the Earth’s atmosphere during sunrise or sunset, shorter wavelengths (blue and violet) are scattered away more effectively by air molecules than longer wavelengths (red and orange). The light that reaches the observer’s eyes is therefore enriched in the longer, redder wavelengths.
– Rayleigh scattering is inversely proportional to the fourth power of the wavelength (scattering ∝ 1/λ⁴), meaning shorter wavelengths are scattered much more than longer wavelengths.
– The path length of sunlight through the atmosphere is longest at sunrise and sunset.