Why is there a day night cycle Why does the phenomenon of day night alternation occur

The Earth's day-night cycle is caused by the Earth's constant rotation.

The earth is a non-luminous and opaque sphere, the sunlight can only illuminate half of the sphere at the same moment, the half of the earth illuminated by sunlight is day, and the half of the earth that is not illuminated by sunlight is night, and the dividing line (circle) between the day hemisphere and the night hemisphere is called the morning and dusk line (circle).

At any given moment, the diurnal state of the various parts of the Earth can be expressed in terms of the height of the sun. Sun altitude is short for solar altitude angle, which indicates the inclination of the sun's rays to the local ground plane. Everywhere in the day hemisphere, the height of the Sun is always greater than 0 degrees, that is, the Sun is above the horizon; Everywhere along the morning and dusk lines, the height of the sun is equal to 2 degrees, that is, the sun is just above the horizon; Everywhere in the night hemisphere, the height of the Sun is always less than 0 degrees, that is, the Sun is below the horizon.

Because the earth is constantly moving, day and night are constantly alternating. The cycle of day and night, or the diurnal variation of the height of the sun, is 24 hours and is called a solar day. The solar day restricts human daily life and rest, so it is used as the basic unit of time.

In addition, the short duration of the solar day prevents the entire Earth's surface from heating and cooling too violently, thus ensuring the survival and development of living organisms on Earth.

Since the earth rotates, the earth's surface enters with its rotation"Facing the sun"→"Turn your back to the sun"→"Facing the sun"→"Turn your back to the sun"so that people who have been in this area see the alternation of day and night.

Day and night are a combination of day and night. The alternation of day and night is a natural phenomenon formed by the rotation of the earth under the irradiation of the sun.

We live on the earth with one half of the sphere facing the sun and the other half of the sphere facing away from the sun, and those who stay in the half of the sphere facing the sun live in the daytime, and those who stay in the half of the sphere facing away from the sun live in the night. Because the earth is constantly rotating, there is an alternation of day and night in every part of the earth.

Five days and nights.

The meaning of the alternation of day and night is to make the creatures on the earth sleep, get a time to rest, which is conducive to recuperation, and also so that the side of the earth facing the sun will not get too hot, so that the side of the earth facing away from the sun will not be too cold.

The earth is a non-luminous and opaque sphere, the sunlight can only illuminate half of the sphere at the same moment, the half of the earth illuminated by sunlight is day, and the half of the earth that is not illuminated by sunlight is night, and the dividing line (circle) between the day hemisphere and the night hemisphere is called the morning and dusk line (circle).

The Earth's rotation is formed.

We experience the alternation of day and night every day, which is caused by the constant rotation of the earth. If both the Sun and the Earth are electrically charged, when the Sun rotates, it will be affected by the center of the universe, generating a strong rotational current, and this current will produce a rotating electromagnetic field.

At this time, the earth will also generate an induced electromagnetic field to hinder the rotation of the sun's electromagnetic field, and this induced electromagnetic field will promote the rotation of the earth and form the rotation of the earth.

To use a simple analogy, the rotation of a figure skater slows down when the arms are extended, because the radius of the rotating body increases, and the angular momentum is conserved, and its linear velocity inevitably decreases; Conversely, if the arms are folded together, the rotation speed increases. It is precisely because of the wonderful law of "conservation of angular momentum" that all other planets and various celestial bodies today are self-rotating.

It wasn't until Copernicus proposed that the Earth is also a planet, orbiting the Sun while rotating itself on its axis, that the principle of the alternation of day and night was understood.

The above content reference: Encyclopedia - day and night alternation.

The reason for the alternation of day and night is that the earth is constantly rotating.

The earth is a non-luminous and opaque sphere, sunlight can only illuminate half of the globe at the same moment, half of the globe illuminated by sunlight is day, half of the globe that is not illuminated by sunlight is night, and the dividing line between the day hemisphere and the night hemisphere is the morning and dusk line.

Extended material: Because of the rotation of the earth, the conditions of day and night at the same time in different parts of the earth are different, some are noon, some are midnight, and some are experiencing the alternation of day and night in the morning, dawn or dusk. When the sun rises in a province to the maximum part of the day, the sun's rays only shine on the meridian where the city is located, which is the local noon.

Since the Earth's axis is tilted, the length of day and night varies in different parts of the Earth. In the north and south poles of the earth, the sun shines obliquely throughout the year, and the length of day and night varies the most.

In the high latitudes of the northern and southern hemispheres, the sun does not set or does not rise all day long, that is, it is day or night 24 hours a day, which is the polar day and night phenomenon in the polar regions. At the North and South Poles, there are polar days and nights that last for half a year.

The earth is a sphere that neither emits light nor is transparent, and the sun can only reach half of the earth, and the other half cannot shine, only night, so that the phenomenon of day and night (note that it is not the phenomenon of alternation of day and night).

The reason for the alternation of day and night is the rotation of the earth, because of the existence of the earth's diurnal phenomenon, and the earth itself is constantly rotating, so the alternation of day and night will occur.

So the main reason for the day-night cycle is that the rotation of the Earth is available in textbooks.

Interpretation of day and night.

1) [day and night;Round the clock] day and night day and night day and night business life and death, day and night things also. ——Song Wen Tianxiang, "Guidebook" Afterword, Day and night. ——History of the Ming Dynasty (2) and day and night, day and night.

Guangdong Military Affairs" Detailed Explanation (1).Day and night. The Analects of Zihan:

The deceased is like a husband, reluctant to give up day and night! Tang Yuanzhi's poem "Humanity is Short": "The way of heaven has never lived day and night, and it is busy in spring, autumn, winter and summer.

Lao She's fourth paragraph of "Erma" is suspicious of key nine: "Pastor Yi's face has lost a little weight, because he has broken two dictionaries because he has read Chinese books day and night, and he can't understand it. ”2).

Refers to the two opposing forces of all things, the power of growth and decline, or the two aspects of yin and yang. "Yi Zhi Ci I": The rigid and soft, the image of day and night.

Gao Heng Note: "This cloud day and night is covered with day and night to represent yin and yang. " Yi Zhi Zhi Shang :

It is known by the way of day and night. Gao Heng noted: "Jiao Xun said:

The way of day and night is the way of one yin and one yang. 'Reading is wisdom. This statement of the Book of Changes runs through the law of the transformation of yin and yang opposites and has wisdom, which can predict good luck and evil.

Word decomposition Interpretation of 昼 昼 (昼) ò日: day and night. Daylight (daytime).

Night radical : day; Interpretation of 夜 夜 è the time when it is dark , as opposed to "day" or "day" : night.

Day and night. Nightshade (When the night is coming to an end). Night blindness.

Night. Supper. Night talk.

Night Raid. Nocturnal (妌). Night Fight.

Day radical: Night.