Li Mengxi remembered that at that time, he always told his grandfather the date of the Gregorian calendar without even thinking about it.

Every time, grandpa would look up by himself. If there was a moon in the sky, grandpa would be able to tell what day it was after looking at it for a while. When he told me the first day of the lunar calendar, he would always say that he was wrong and yell at grandpa.

stubborn.

The lunar calendar date and the solar calendar date are never on the same day. Just like my grandfather, who has only understood the lunar calendar all his life, and myself, who only understand the solar calendar, are in the wrong era.

Grandpa is illiterate and cannot read a calendar even if he has one. Whenever the loudspeaker in the village calls out the date for paying water and electricity bills or distributing food subsidies, Grandpa always has to ask someone what day it is on the lunar calendar.

Now, I can only determine the time by looking at the moon.

Li Mengxi's mind was racing. He opened his eyes and looked at the sky, thinking of many things. The moon was also falling from the center of the sky to one side bit by bit.

Li Mengxi can roughly tell the time.

The moon moves little by little in the sky, Zi hour, Chou hour, Yin hour...

Then, the moon disappeared and the sky dawned.

My little brother woke up.

Unknowingly, I was in a daze all night.

The sun has risen from the east, and the sky is bright.

When does the sun rise?

Early in the morning, it should be Chen time.

Zi Chou Yin Mao, Chen Si Wu.

From morning to noon, three hours.

One hour and two hours.

Three hours, six hours.

From 6 a.m. to 12 p.m., that's just enough.

Li Mengxi felt very happy because he had a sense of enrichment with knowledge.

In comparison, having a stuffy nose that seems to have a cold due to staying in the cold night all night is insignificant.

——

On the second day of August, it was still a day of marching.

During the march, Li Mengxi opened the car windows and frequently observed the sun in the sky to practice how to identify the time.

In the previous life, during the nine-year compulsory education stage, especially in junior high school, in addition to the three main subjects of Chinese and Mathematics, there were also three minor subjects of physics, biochemistry. In addition, there were no college entrance examinations such as history, geography, ideological and political education.

s things.

At that time, many people thought that geography and the like were of little use. When Li Mengxi was a student, he also felt that geography classes were just for enriching knowledge.

However, I didn't expect that the remaining things that I had almost forgotten after I learned them, but still remembered them, would actually be of great use now.

Just like now, how to tell the time during the day.

Li Mengxi looked at the sun in the sky, the vast sky and the earth under the sky, and some abstract geometric figures magically appeared in his mind.

There are two reasons why the graphics appear.

One is that a certain illustration in a junior high school geography textbook uses a schematic diagram of a semicircle to introduce the movement of the sun.

According to the change of time, the layout of the solar pattern diagram is generally similar to the layout of the clock scale.

In other words, during the day, the shape formed by the sun in the sky and on the ground is a semicircle.

The sun moves at a roughly constant speed relative to the earth. In this case, if you use a protractor to measure the angle that the sun turns after it rises from the eastern horizon, and then calculate how much the angle is equal to 180 degrees, you can calculate the proportion.

The calculated daylight time.

For example, if the sun rotates ninety degrees from the horizon, that is, the angle between the sun and the ground changes from 0 degrees to 90 degrees.

So, it's noon now.

Then, the time at this time is half the length of the day.

And if, the angle of the sun's rotation is 45 degrees.

Then, a quarter of the daytime has passed.

That is, about nine o'clock in the morning.

In the same way, when the sun turns 180 degrees, it sets. It turns 180 degrees from the east and sets exactly 180 degrees when it reaches the west horizon.

The rising and setting trajectory of the sun is a semicircle, and a semicircle is 180 degrees.

These two bits of knowledge, one comes from a junior high school geography textbook and the other comes from elementary school mathematics. The significance of these two bits of knowledge at this time is that it made Li Mengxi realize that if the angle of rotation of the sun can be accurately measured, then it can be measured extremely accurately.

Out of time.

The ancient timekeeping sundial was also based on this principle. However, the sundial did not directly use the angle of the sun, but used the sun to illuminate the shadow of the dial needle, which is indirect use.

Li Mengxi stared at the sun in the sky for a long time. He couldn't tell whether the sun's angle was about 45 degrees or more than 30 degrees.

The human eye has limited observation capabilities.

This chapter is not over yet, please click on the next page to continue reading! Because it is 180 degrees, and because it is measuring angles, Li Mengxi naturally thought of a protractor.

How about making a protractor?

Once the idea came up, Li Mengxi felt it was worth a try.

Those related to the sun and sky should be astronomical knowledge, or at worst, geographical knowledge.

Li Mengxi thought that his knowledge of astronomy and geography was shallow and he was almost illiterate.

But, what about trying it?

What if it's just a protractor that's really useful?

If you really look at the sun and measure it against the horizon, you can easily calculate the angle of the sun and get the extremely accurate time.

In this way, you can be said to be able to observe the weather, and understand astronomy and geography, right?

Others, such as the coachman Lao Tie, relied on his rich experience in agricultural production and could tell the approximate time just by looking up, and it could be accurate to within half an hour.

That is to say, when there is sun, experienced farmers can control the time error within one hour.

That is to say, casually it would be somewhere around seven or eight, or eight or nine.

But this is not enough.

If it is wartime and the time cannot be accurately judged, and the time error is as large as an hour, then suppose that we need to make an emergency assault on an enemy camp while it is still dark.

However, because you cannot accurately judge the time, you must know that in the evening, it will be dark when it is said to be dark. It was still bright five minutes ago, but it will be completely dark five minutes later. Five minutes is enough to make a big difference, let alone an hour and a half error.

It's been hours.

Then, if the accuracy of time estimation is relatively high, a lot of confusion caused by time factors can be avoided in military arrangements.

For example, judging from the sky, it was estimated that it would get dark in half an hour, and half an hour was enough to travel, so the army was ordered to move out.

As a result, within twenty minutes, it became dark.

The attack was stopped halfway, and they had to retreat, which was a waste of military morale.

And if the time estimation accuracy was higher, there would be no such trouble.
Chapter completed!