Where are the people standing in the WeChat startup screen?

This picture shows the famous Earth photo "Blue Marbles" taken by the crew of Apollo 17 spacecraft, not taken on the moon. Then, if you don't know this background, can you infer the information that the landlord needs?

Yes! This answer tries to judge the background, position and surrounding environment of this villain only from the information given in the picture.

Let's judge the position first.

First of all, the villain looks at the center of the earth, and the connection between our line of sight and the center of the earth will fall at the center of the earth. So draw a picture, draw two diameters, and the intersection point A is the center of the circle. In other words, the position of the villain is just above point A. If you are a liberal arts student like me, you must be familiar with the globe. You will find the African continent to the west of point A, and Madagascar to the northeast.

Then just check the latitude and longitude of point A, and you can know where the villain is above the earth. At this time, we need a globe. I turned on Google Earth software.

As shown in the figure, rotate the earth to this angle in Google Earth software and mark point A. The latitude and longitude coordinates of this point can be found directly in the bottom column of the software: about 30 south latitude and 37 east longitude.

In other words, as long as we are at any point in the space above this point, we can get this perspective.

But, pay attention! Not too close. If you get too close, you can't see the edge of the earth at all. The visual angle of human eyes is basically around 120. If you are too close to the earth, the earth will fill your field of vision, so you should take this photo at least within a certain interval from the earth.

The lower limit of the interval is to put the earth comfortably in the middle of your field of vision, at least according to the requirements of the visual angle, leaving some blanks beside it. I am too lazy to forget. Fortunately, Google Earth has cheating function. You just need to put the earth in a comfortable position in your field of vision, and it will automatically help you calculate your height. I simulated it, and the height is not less than 25 thousand kilometers. The Apollo 17 spacecraft took this photo at an altitude of 45,000 kilometers, which is within this altitude range.

What about the upper limit of the interval? Can it be infinite?

Theoretically, as long as you have a telephoto lens, you can see this angle of the earth. Even if you are a light year away, you can take this photo with a super super telephoto lens (but please note that on the scale of a light year, you can pose at that position a light year later, and then the light can reach the lens a light year away). As long as there is only this little friend between your lens and the earth, there is nothing to stop it.

The final answer is that as long as you are in the sky near the point of 30 south latitude and 37 east longitude of the earth, more than 25,000 kilometers away from the surface of the earth, and there is no obstacle between the camera and the earth, you can see this scene, and then this little man stands in front of you.

So, is it possible for this little friend to stand on the moon? It depends on whether it is possible for the moon to move above this point, and the distance is also within this interval.

The answer is, there is a little possibility.

If the moon wants to run directly above point A, the intersection angle between the connecting line between the moon and the center of the earth and the equatorial plane of the earth must be equal to the latitude of the point, and the intersection angle cannot be greater than the intersection angle between the running surface (ecliptic plane) and the autobody surface (equatorial plane) of the earth.

According to astronomical calculation, the intersection angle of white and red is constantly changing, and it changes periodically between 18 17' and 28 35'. In other words, the direct point of the moon can point to 28.5 south latitude as far as possible. The latitude of point A is 30 degrees. The difference is 1.5, but considering that when I use Google Earth to measure, there may be an error of 1.5, which means that the moon may be above point A.

Then how to judge at this time?

Judging the moon phase first, we have inferred that the moon is between the sun and the earth, so it must be a new moon, that is, around the first day of the first lunar month.

The change period of the intersection angle between white and red is 18 1 1 day and 8 hours. 1165438+0 days and 8 hours in 2008, which is called a "Sharo cycle". Although we fans of "Three-body" know that there is no solution to three-body motion except for a few limited forms. Fortunately, the masses of the sun, the earth and the moon are quite different, and the general situation is basically solvable. Every time the sun, the earth and the moon go through an 8-hour Sharo cycle of 18 1 1 day, their positions will cycle. There will be 43 eclipses and 28 eclipses in each Charlotte cycle, which means that after an eclipse on the earth, this eclipse will happen again after a Charlotte cycle. So if you want the moon to move above this point, you have to wait 18 years to miss a cycle.

The last year of lunar declination is from 2005 to 2007. If this chart is established, it needs to be selected within these three years (of course, it can also be counted before and after one or several Sharo cycles). But even in 2005-2007, not every day. Because, in order to make the moon point directly at the southernmost tip of the new moon, it must be around the winter solstice in 65438+February. Why? Please look at the picture below. The ecliptic and Bai Daochang are like this:

In order for the moon to shine directly to the south, the moon and the sun must run at the maximum intersection angle to the southernmost point on the left side of the map. At this time, the moon points directly at 28.5 south latitude of the earth, and the sun points directly near the tropic of Capricorn, so that the moon is located between the sun and the earth, and it is possible to meet the conditions of "new moon" and "southernmost moon".

Then look at the perpetual calendar to see if the winter solstice in the year when white and red intersect the most also happens to be a new moon. The winter solstice in 2005 is the 22nd, excluding the first quarter moon. The winter solstice in 2007 is thirteen, and it's almost full moon. No way. In 2006, the third day of the solstice winter, ah, this day is almost the same, not bad! The day before winter is the second day of solstice, and the effect is good!

So, is this picture on the WeChat welcome page the solstice of winter?

It really is!

The Antarctic circle in the south of this picture is all lit up! This is the polar day in the Antarctic circle, and it is also around the winter solstice! No contradiction! Meet the conditions of the "southernmost new moon"! Great!

It is much easier to calculate the local time. The direct point of the sun is about 37 east longitude, and the local time of this longitude is noon 12, and the earth rotates every hour 15. At this time, it is expected to be around 9: 30 am GMT.

Finally, infer the environment.

1. If a buddy is standing on the moon, because his back and nearby ground are not illuminated by the sun behind him, and he can see the earth, it can be inferred that he is either standing on the back of the moon or something is blocking the sun behind him.

2. The little friend saw the north above the earth, which proved that he was standing in the northern hemisphere of the moon.

3. The little friend is definitely not standing directly on the ground of the moon, because the place he stepped on is too curved. He has to stand on a spherical dome (just like the roof of the National Grand Theatre), and then the photographer takes pictures with a telephoto lens in the distance, projecting the figure of his little friend on the round surface of the earth, which is particularly lonely. The photographic techniques used are as follows:

Summary:

1. As long as this little friend is standing in the sky near the point of 30 south latitude and 37 east longitude, which is more than 25,000 kilometers away from the earth's surface, and there is no obstacle between the lens and the earth, the photographer can shoot with the telephoto lens from behind, choose any winter solstice (ensure that the Antarctic circle is extremely bright), and wait until 9: 30 GMT to shoot the main screen of WeChat.

2. If shooting on the moon, the following conditions shall be met:

In 2006, at 9: 30 GMT, on the third day of the third lunar month from winter to morning, the moon moved to the southernmost point, with the maximum intersection angle of 28.5, and directly hit the earth near 28.5 south latitude. At this moment, a little man is standing on the side of the moon facing the earth, a circular bump in the northern hemisphere. You stand behind him with a telephoto lens. Wow, you took this photo.

In fact, this probability is really small, but at least it may not be.