Why the time of day is not about 12 o clock symmetry

This question requires you to get a globe.

to draw the morning and dusk lines.

(The morning and dusk lines are the circles that must cross the north-south direction of the equator, you can draw it, hehe) Then, you find the morning and dusk lines and the equator, the Tropic of Cancer, and the 30 degrees north latitude respectively.

40 degrees north latitude, 60 degrees north latitude (in addition to the equator must be selected, other latitudes can be arbitrarily selected, the degree is uncertain, it is convenient to find which one) and other intersections of these latitudes, each latitude and the morning and dusk lines have two intersection points, the meaning of these two intersections is, one is the sunrise time (point A), the other is the sunset time (point B). The next step is to find the arc formed by the morning and dusk lines of the selected parallels, which represent the daytime section (arc ab), and the meaning of the midpoint of each arc is the 12 points of latitude (point c). Then you will find that the morning and dusk line only intersects the equator, the distance from point A to point C (i.e., arc AC) = the distance from point B to point C (i.e., arc Cb), which means that only on the equator, any season is sunrise at 6 o'clock, sunset at 18 o'clock (this can also be pushed out to drop), and symmetrical with 12 o'clock noon.

Elsewhere, the arc AC and arc CB are also equal, that is, they are both symmetrical to 12 points!! The question arises, so why isn't it in fact? Taking Shanghai as an example, in fact, the "12" o'clock in Shanghai is not the 12 o'clock local time we say, that is, it is not the C point we have here.

In order to unify the whole country, Shanghai also adopts the East 8th District of Beijing's time zone.

time, in fact, when the city of Shanghai"12 o'clock"(Beijing is exactly 12 o'clock), she is actually past 12 o'clock local time, because Shanghai is east of Beijing, the time is earlier than Beijing, just like Tokyo time is earlier than Beijing. This is what we call jet lag. It is a geographical phenomenon that is the rotation of the earth.

results. Oh, love the earth, love geography, love life!

This is because, on the one hand, the noon time corresponding to each place is actually different, but in order to facilitate the management of the region, the noon time is actually the same in different regions. For example, China uses the time in Beijing's time zone, while the actual noon time in Urumqi should be more than an hour after noon in Beijing time, so it will not be symmetrical. On the other hand, the Earth's morning and dusk lines are not at a fixed angle to the equator, but change every moment, and noon time cannot be corrected from time to time, so the sunrise and sunset times will not be symmetrical every day.

Because the earth's axis is tilted, the earth has been rotating at this angle, and then revolves around the sun, so the direct sun point will go back and forth between the Tropic of Cancer, so the northern hemisphere has the longest day during the summer solstice of the year (the direct sun reaches the Tropic of Capricorn, and the northern hemisphere receives the longest period of light), the northern hemisphere has the longest night at the winter solstice (the direct sun is at the Tropic of Capricorn), the spring equinox and the autumn equinox are 2 days, and the direct sun point is just on the equator, so there are only these 2 days in the whole year, and the day and night are of equal length. The rotation and revolution occur at the same time, and the direct point of the sun also changes every day, so the time of sunrise and sunset changes every day.

After reading the answers of other netizens, I can't help but think about your question:

1.Taking Shanghai as an example, if Shanghai uses a local place, the sunrise and sunset times must be symmetrical at 12 noon.

2.Now Shanghai uses Beijing time (120 degrees east longitude), and Shanghai is actually located east of 120 degrees east longitude, when Beijing time is 12 o'clock, Shanghai's local time is also past 12 o'clock (at this time Shanghai looks at the sun has been west), so Shanghai has a long morning time and a short afternoon time.

3.If you can ask this question, you are a thinker.

4.We are willing to learn and communicate with you

The yellow-red angle is 23°26, so the Earth's axis is not perpendicular. The length of the day varies with the direction of movement of the direct point of the sun. So it has nothing to do with time. At 12 noon, the highest altitude of the sun is only for 12 o'clock local time, and has nothing to do with going time.

The sunrise and sunset are different times in each place, and the time used for timing is the same (in the same region), so the sunrise and sunset times on the midline of the standard time zone are not symmetrical about 12 noon.

The earth is divided by latitude and longitude, latitude is east-west, divided into 90 degrees of north and south latitude, longitude is north-south direction, divided into east and west 180 degrees, the division of time is divided according to longitude, our time in China is Beijing time, to be precise, it is the time of 120 degrees east longitude, and only on the meridian of 120 degrees east longitude is symmetrical.

The sunrise and sunset time at 12 o'clock is symmetrical and is calculated based on local local time.

It is calculated about the length of day and night, because as the earth rotates and revolutions, its sunrise and sunset times also change.

Only the spring and autumn equinoxes are symmetrical in the day and night, and none else.

First of all, the earth is not a regular circle, and secondly, there is the existence of yellow and red angles.

That's determined by the rotation of the Earth.

Only the equinoxes of day and night will be symmetrical.

When the sun shines directly on the equator, the day and night are of equal length across the globe.

tilt, the earth has been rotating at this angle, and then revolves around the sun, so the sun.

Twelve o'clock is defined as the twelve o'clock of the day when the sun is at its highest (the sun angle is at its highest). So the middle of the day must be twelve o'clock. Of course, this twelve o'clock refers to the local time.

The reason for this definition is that it is not observant.

Obviously, China uses Beijing time, and the local time in Beijing is used as the unified time for the whole country. It's just for the convenience of work and life.

In addition to Beijing time, there is also London time or something.

The United States is divided into Eastern Time and Western Time.

Who told you that the middle of the day must be 12 o'clock, the easternmost and westernmost time zones of the mainland are all in Beijing time, Xinjiang is 2 hours behind Beijing, Beijing noon is 12 o'clock, Xinjiang noon is about 2 o'clock Beijing time.

There is no saying that the middle of the day must be 12 o'clock.

【Noon】Midday, also known as sunday, noon, etc.: (11 o'clock to 13 o'clock).

The old man said that it was not advisable to go out from 12 o'clock to 12:30 o'clock at noon because the evil spirit was too heavy! Prone to accidents!

A custom that can be one minute earlier, or one minute later, and naturally fine.

The sun is too big, the traffic is too congested, it's time to eat.

It's a bit superstitious, and I don't know very well, but this may be that your family is worried about your safety and doesn't want you to come out, which is also a good intention.

Yes, yes is about equatorial symmetry. Because 18 o'clock is the time at the intersection of the dusk line and the equator. At sunset, the 18-point symmetry illustrates two points:

1.Both places are on the great circle of the morning and dusk line. 2.

The two places are equal in length from the equator. So it's about equatorial symmetry

I don't quite understand your "the time of the fall of the sun in the same day and the sun is about 18 o'clock", I don't know how this symmetry is symmetrical?

In short, if the length of the day in place A is equal to the length of the night in the place of remembrance, then the latitude of the two places is the same, one in the northern hemisphere and the other in the southern hemisphere, that is, about the equatorial symmetry.

The time of the whole mu of jujube country is the same, the Beijing time of the eighth district of Gaonainadong. How is Qingdao different? **The bottom is the time of sunrise and sunset, not the time of morning and afternoon.

It is morning until dawn and before 12 noon, and afternoon before dark. Around 12 noon can be called noon.

It is not 12 o'clock to divide the time of the day at one point on the earth into equal day and night, it should be said that it is artificial, and the time of any point on the earth is divided into two time periods equal to day and night, because the rotation of the earth around the earth's axis is about 24 hours, so it is set at 12 o'clock in the evening, which is the end of the day, and 0 o'clock and 24 o'clock coincide, so it is the beginning of the next day. Therefore, 12 noon is noon.

Geographically, the sun reaches its highest at 12 o'clock.

You say 12 p.m. or 12 noon.

It doesn't have to be equal! ~

Daylight is the time between sunrise and sunset.

However, 12 noon (noon) is not necessarily the middle time period, and like our Beijing time, it is estimated that only the longitude area equal to Beijing is noon, and 12 o'clock is the middle of the day!

The solar altitude reaches its maximum at noon, and the solar altitude angle at sunrise and sunset is zero. The angular velocity of the Earth's rotation is constant, so the angle of the sun's altitude changes in the same time, and the sunrise to noon is equal to the noon to sunset time.

According to the principle of symmetry, i.e., with 0 and 12 o'clock local time as the axis of symmetry between night and day, the length of time on both sides is the same.

Since the sun is at its highest at 12 o'clock, the time from 4:30 to 12 o'clock is also equal to the time from 12 o'clock to sunset. The first half is 7 and a half hours, then the second half is also 7 and a half hours, and the sunset time should be 19:30.

12 4:30 7:30 (morning daylight hours), 7:30 2 15 (hours). So it should be 19:30 sunset.