When the Sun is near the horizon during the morning or evening, it appears reddish. The phenomenon that is responsible for this observation is

The reddish appearance of the Sun near the horizon during sunrise and sunset is primarily due to the scattering of light. According to Rayleigh scattering, air molecules and fine particles in the atmosphere scatter shorter wavelengths (blue and violet) more effectively than longer wavelengths (red) [3]. When the Sun is near the horizon, sunlight must travel through a much thicker layer of the atmosphere to reach the observer's eyes [4]. During this long journey, most of the blue light is scattered away and removed from the direct line of sight. Consequently, the light that reaches the observer consists mainly of longer wavelengths, such as red and orange, giving the Sun its characteristic reddish hue [4]. While atmospheric refraction causes the Sun to appear slightly higher or flattened, it is the scattering process that determines the color [5].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169
2. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Solid Particles > p. 273
3. [2] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > Advance sunrise and delayed sunset > p. 168
4. [4] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > The Passage of Solar Radiation through the Atmosphere > p. 68
5. [5] https://spaceplace.nasa.gov/blue-sky/