Why does the sun rise during the day and set at night?
In our daily lives, the phenomenon of the sun rising and setting seems to be very common, but there are complex and subtle astronomical principles behind it. The phenomenon of the sun rising during the day and setting at night is the result of the combined effects of many factors, including the rotation of the earth, the change in the solar altitude angle, the division of time zones, and the optical effects of the atmosphere.
1. The relative position of the Earth's rotation and the Sun
The Sun is the central star of our solar system, and the Earth is one of the planets orbiting it. The Earth is also rotating, spinning on its own axis, and it takes about 24 hours to complete one rotation. This rotation causes the surface of the Earth to change constantly: one side faces the Sun, and the other side faces away from the Sun.
It is because of the rotation of the earth that we can see the sun rise during the day and set at night. When the earth's rotation makes the surface of a particular area face the sun, we can see the sun rise from the horizon and shine on the earth; and when the earth continues to rotate and makes the surface of the same area away from the sun, the sun will gradually fall below the horizon and night will fall.
2. Changes in the solar altitude angle
The solar altitude angle refers to the angle between the sun's rays and the earth's surface. During the day, as the earth rotates, the sun's altitude angle gradually increases until the sun reaches its highest point of the day. At this time, the sun's rays shine on the earth's surface in the most direct way, making the day warm and bright.
At night, the Earth continues to rotate, the sun's altitude angle gradually decreases, and the sun's rays become more oblique. Eventually, the sun falls below the horizon, the sky gradually darkens, and night begins to fall.
3. Time zones and day and night changes
Different regions on Earth experience different times of day and night because the Earth's rotation speed remains constant, but each region is located at a different longitude. In order to unify time, we divide the Earth's surface into different time zones, each of which uses the local time of its central meridian as the standard time.
Time zones allow us to more accurately predict the time when the sun rises and sets. Although the length of day and night varies in different parts of the world, people in the same time zone can share the same time standard, which also helps us to carry out our daily lives in an orderly manner.
4. The influence of the atmosphere on sunlight
In addition to the Earth's rotation and time zones, the atmosphere also plays a role in the sun rising and setting. Air molecules, water vapor, and particles in the atmosphere scatter and absorb the sun's rays, softening them as they pass through the atmosphere. This is one reason we see beautiful colors in the sky at sunrise and sunset.
In addition, the atmosphere also plays a role in regulating the temperature of the earth. During the day, the atmosphere absorbs the heat of solar radiation, causing the surface temperature to rise; at night, the atmosphere releases the stored heat, slowing down the rate of decrease in surface temperature, thereby reducing the feeling of cold at night.
With a deeper understanding of these astronomical principles, we can more deeply understand and appreciate the wonders of the universe that occur every day , and cherish the beautiful and complex planet we live on.