At night, when the color temperature of sunlight is low, a picture will appear.

Color temperature is not the temperature of color, but the color of the object when it reaches a certain temperature (from atomic physics).

Photography is to use this principle to digitize, identify and calculate different colors.

In the morning and at night, when sunlight passes through the atmosphere horizontally (tangentially), the atmosphere will be thicker. Because the refractive index of the atmosphere is different for different colors of light (electromagnetic waves with different frequencies), at a certain point on the earth, you will see the process of seven-color rainbow in turn, for example, white light is refracted by a prism, but you will see seven colors of light at the same time when you stand on the ground. Because of the low refractive index of red and orange light, the first thing we can see is that red and orange light is defined as low color temperature in photography, while blue and violet light is defined as high color temperature (7000- 1000-2000 degrees), because red and orange light corresponds to the light emitted by low temperature light in physics. When the sun is not above the horizon in the morning or after the sun sets on the horizon in the evening, blue light can only be seen because of its large refractive index. Because the sun is getting stronger in the morning, the color will be covered by strong light, but at night, the sun is getting weaker and weaker, and the color will become clearer and more beautiful. Therefore, the sunset is generally more colorful than the morning glow. During the day, due to the direct sunlight on the ground, the refraction disappears (some of them are also covered by strong light), and only white light is available. In physics, white light means that the surface temperature of the sun is about 5800 degrees Celsius, and the color temperature of white light is 5800K (Calvin, international standard temperature).