During sunrise and sunset the rays have to travel the larger part of the atmosphere because they are very close to the horizon. Therefore light other than red is mostly scattered away. Most of the red light which is the least scattered enter our eyes. Hence the sun and sky appear red.

Why the Sky Appears Red During Sunrise and Sunset?

During sunrise and sunset, the sky often displays vibrant shades of red, orange, and pink. This phenomenon is primarily caused by the scattering of sunlight in the Earth's atmosphere. To understand why the sky appears red during these times, let's explore the science behind it.

Scattering of Light
When sunlight interacts with the Earth's atmosphere, it undergoes a process called scattering. This occurs when light waves interact with particles in the atmosphere and change their direction. The scattering of light is responsible for the beautiful colors we observe in the sky.

Rayleigh Scattering
Rayleigh scattering is the dominant process that causes the sky to appear red during sunrise and sunset. This type of scattering occurs when the sunlight interacts with gas molecules and tiny particles in the atmosphere, such as dust or water droplets.

Wavelength Dependence
Different colors of light have different wavelengths. Blue light has a shorter wavelength, while red light has a longer wavelength. When sunlight passes through the Earth's atmosphere, its shorter blue wavelengths are scattered more easily by the molecules and particles in the air.

Atmospheric Path Length
During sunrise and sunset, the sunlight has to travel a longer path through the Earth's atmosphere. The angle at which the sunlight enters the atmosphere is much shallower, causing it to pass through a greater thickness of air. This increased path length allows more scattering of the shorter blue and green wavelengths.

Red and Orange Dominance
As a result of Rayleigh scattering, the shorter wavelengths of blue and green light are scattered away from our line of sight, while the longer wavelengths of red and orange light continue to pass through the atmosphere relatively unaffected. This leads to the dominance of red and orange hues in the sky during sunrise and sunset.

Atmospheric Conditions
The appearance of the sky during sunrise and sunset can also be influenced by atmospheric conditions. Dust, pollution, and other particles in the air can further scatter and absorb light, causing variations in the colors observed. For example, if there are more particles or pollutants present, the sky may appear more orange or even brownish.

In conclusion, the sky appears red during sunrise and sunset due to the scattering of light in the Earth's atmosphere. The longer wavelengths of red and orange light are less affected by scattering compared to the shorter wavelengths of blue and green light. This phenomenon, known as Rayleigh scattering, creates the beautiful colors we often observe during these times.