The Sun is observed to be reddish when it is near the horizon, i.e., in the morning and the evening. This is because

The reddish appearance of the Sun during sunrise and sunset is primarily due to Rayleigh scattering. Sunlight consists of various colors with different wavelengths; blue light has a shorter wavelength, while red light has a longer wavelength [1]. According to Rayleigh's law, the intensity of scattered light is inversely proportional to the fourth power of its wavelength, meaning shorter wavelengths (blue/violet) are scattered much more effectively than longer ones (red). When the Sun is near the horizon, sunlight must travel through a significantly thicker layer of the Earth's atmosphere. During this longer path, most of the blue and shorter-wavelength light is scattered away in different directions [1]. Consequently, the light that reaches the observer's eye is dominated by the least scattered longer wavelengths, resulting in the characteristic red and orange hues.

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