What is natural light and shadow?

Rainbow, mirage, sunset and aurora all belong to natural light and shadow.

Rainbow: Rainbow is the dispersion and reflection caused by sunlight shining on spherical water droplets in the air. When sunlight enters the water drop, it will be incident at different angles at the same time, and will also be reflected at different angles in the water drop, resulting in the rainbow we see. When this reflection occurs, sunlight enters the water drop, refracts once, then reflects on the back of the water drop, and finally refracts again when it leaves the water drop. Because water has a dispersive effect on light, the refractive index of light with different wavelengths is different, and the refractive angle of blue light is greater than that of red light. Because the light is reflected in the water droplets, the spectrum seen by the observer is reversed, with red light at the top and other colors at the bottom in turn.

Mirage: It is caused by the refraction and total internal reflection of light in the air. Air itself is not a homogeneous medium. Generally speaking, its density decreases with the increase of height. The higher the height, the smaller the density. When light passes through the air layer at different heights, it will always cause some refraction, but this kind of refraction phenomenon has become accustomed to our daily life, so we don't feel anything strange. However, when the air temperature changes vertically, it will lead to different refraction and total reflection, resulting in a mirage. Mirages mostly occur in the sea and desert, and can be seen occasionally on asphalt roads in summer.

Xia: At sunrise and sunset, colorful clouds often appear on the horizon. The morning glow and sunset glow are caused by the scattering of light by air. When sunlight enters the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere. ? As the saying goes, "Don't go out at sunrise, but go to Wan Li Road at sunset". In other words, the bright red glow in the morning shows that there are many water droplets in the atmosphere, which indicates that it will rain. If there is a fiery red or golden sunset glow, it means that there is no cloud in the west, and the sunlight can be transmitted to form a sunset glow, which indicates that the weather will be fine.

Aurora: Aurora is a unique atmospheric luminous phenomenon in the North and South poles, leaving a beautiful figure in the myths and legends of the East and the West. Aurora is also recorded in China's ancient book Shan Hai Jing. It is said that there is a fairy in the north. She looks like a red snake and shines in the night sky. Its name is Molong. Touching the dragon is like the description in the next paragraph: "The human face snakes, red, and thousands of miles long. It is also the god of Zhongshan. " The Candle dragon referred to here is actually the aurora.