The reason why the sky appears red at sunrise and sunset involves the fundamentals of physics and chemistry. This article will introduce this phenomenon in detail and discuss the optical properties of the atmosphere, the spectral composition of sunlight, the composition of the Earth's atmosphere, and the effects of spectral scattering and reflection.
1. Optical properties of the atmosphere.
The atmosphere is made up of a variety of gases and particles, including nitrogen, oxygen, water vapor and dust. These gases and particles have different absorption, scattering, and reflection properties for different wavelengths of light. In the visible range, the atmosphere has some scattering of light of various wavelengths, but to varying degrees. Blue and violet light are more likely to be scattered by tiny particles in the atmosphere due to their shorter wavelengths, so the sky has a blue background color.
2. The spectral composition of sunlight.
The light emitted by the sun is a continuous spectrum that includes all wavelengths from ultraviolet to infrared. At the core of the Sun, the high-temperature and high-pressure environment causes the hydrogen nuclei to fuse into helium nuclei, releasing a large amount of energy at the same time. This energy radiates into space in the form of light and heat, forming the spectrum of the sun. In the spectrum of the sun, blue and violet light have higher energy, while red light has lower energy.
3. The composition of the Earth's atmosphere.
The Earth's atmosphere is mainly composed of nitrogen, oxygen, water vapor, and particulate matter. The distribution and concentration of these gases and particulate matter affect the optical properties of the atmosphere. For example, when the atmosphere has a high level of water vapor, the atmosphere is more likely to scatter blue light, making the sky appear bluer. At sunrise and sunset, sunlight travels through a longer layer of the atmosphere, making red light more easily scattered and reflected.
4. Effects of spectral scattering and reflection.
At sunrise and sunset, sunlight needs to pass through a longer layer of the atmosphere, making red light more easily scattered and reflected. At the same time, due to the strong scattering effect of the atmosphere on blue light, blue light is scattered as it passes through the atmosphere, while red light is relatively less scattered. Therefore, when sunlight passes through the atmosphere and reaches the observer, there is a relatively high component of red light, giving the sky a red background color.
In addition, the scattering of sunlight by the Earth's atmosphere is also affected by the density of the atmosphere. As the altitude increases, the density of the atmosphere gradually decreases, and the scattering effect on sunlight gradually decreases. As a result, sunlight needs to pass through a longer layer of the atmosphere at sunrise and sunset, making it easier for red light to be scattered and reflected into the observer's eye.
V. Conclusions. In summary, the reason why the sky appears red at sunrise and sunset is due to the relatively strong scattering and reflection of red light and the relatively weak scattering of blue light as sunlight passes through a longer atmosphere. This phenomenon is the result of a combination of the optical properties of the atmosphere and the composition of the Earth's atmosphere.
Wen Amy melon peel.