Why does the sun look yellow at the time of sunrise and sunset?

 

The sun appears yellow, orange, or red during sunrise and sunset because of the way that the Earth's atmosphere scatters sunlight.

When the sun is near the horizon, its light has to pass through more of the Earth's atmosphere than it does when it is overhead. This causes the shorter wavelengths of light, such as blue and green, to scatter more, while the longer wavelengths, such as yellow and red, scatter less. As a result, more of the yellow and red light reaches our eyes, giving the sun a yellow, orange, or red appearance.

This effect is known as Rayleigh scattering, named after the British physicist Lord Rayleigh, who first explained the phenomenon in the late 19th century. The same effect is responsible for the blue color of the sky during the day, as well as the orange and red hues seen during sunrise and sunset.