In all fairness! On July 14, some netizens took a video of a suspected mirage on the sea surface of Xiyong in Shenzhen, and found that there were two suspended ships in the distant sea (the following two pictures), but then after expert explanation, it was believed that it was not a mirage, but just a simple optical illusion (caused by the color of the sea and sky in the distance).
It was only a day later, on July 15, someone found a mirage on the sea surface of Dapeng Bay in Shenzhen, see the following picture:
According to the Shenzhen Evening News, around 9:00 to 10:00 a.m. on July 15, a reporter was photographing a Brisk whale, and just as he was concentrating, his companion suddenly noticed a black shadow appearing above the sea surface on the south side of Pingzhou Island.
After that, the reporter sent this photo to Tian Zheng, captain of the Yantian Brigade of the Shenzhen Marine Comprehensive Law Enforcement Detachment, and the captain replied: This is indeed a mirage, and the fish-shaped part is likely to be part of Pingzhou Island, and then the pole-shaped object on the right should be a beacon on the nearby sea surface. Finally, he added that mirages have also been seen on daily patrols before, but they are not common.
To add here, the report also said that an image of a mirage on the north side of Pingzhou Island was also taken, but this photo was not given (I searched the Internet for a while and still did not find it), so I will not introduce it here. In addition, the reporter originally wanted to record this miracle with video, but because the sea was surging and it was difficult to capture the picture, he gave up.
In fact, there are three types of mirages in Shanghai, namely: upper, lower and lateral mirages, but no matter which kind of mirage, the core principles they involve are the same, that is, the refraction of light and total reflection.
So let's first understand what refraction and total reflection are
Simply put, the so-called refraction refers to the fact that after the light enters another medium from one medium, the two propagation paths are no longer parallel and coincident, but are broken. In one of the most common examples, when we insert a pen into a cup filled with water, we will find that the pen that was originally straight seems to be broken.
The above statement is a simple description of refraction, but qualitatively speaking, we have the conclusion that when light rays enter a medium with a small refractive index into another medium with a large refractive index, the angle of incidence will be greater than the angle of refraction.
But there is also an extreme situation here, that is, when the angle of incidence reaches a critical value, the refraction phenomenon will no longer appear, but will form a total reflection phenomenon similar to specular reflection (still look at the above GIF), note: this phenomenon only occurs when the light rays shoot from a medium with a high refractive index to a medium with a low refractive index (in other words, when the light rays shoot from water to air, after the angle of incidence meets a certain angle, total reflection will occur)
Now we can analyze the formation of the mirage
Take the mirage seen in Dapeng Bay, Shenzhen as an example, because the place where it occurred is located on the surface of the sea, so the process is shown in the following figure (note that the physical object in this picture is a castle, but it does not prevent us from analyzing):
First of all, we need to determine how the temperature of different altitudes is, it is currently in the summer, according to our normal thinking, the temperature should be closer to the surface and the hotter (just like the difference between surface temperature and temperature), but this conclusion is only directly on part of the land, because the place of the incident is located on the sea surface, and we know that the temperature fluctuations of the seawater are relatively slow, and the evaporation of the seawater surface will take away the heat, so compared to the temperature within a certain height above the sea surface, the sea surface is relatively cold.
When the temperature is lower, the refractive index of the air will be higher, so in general, from the bottom up, the refractive index of the air is gradually decreasing.
The most critical point above is finished, and there is still one sub-point, that is, where the original scenery of the mirage is, because this determines what scenery you will see, according to this example, the original scene is Pingzhou Island in the sea and nearby objects, but in the picture just now, we use the castle to replace it.
Due to the curvature of the earth's surface, it means that when a person stands, the range of what he can see is limited, and if there is no mirage, then the castle is invisible to him. But at this time, because the weather conditions are more suitable, so when the light emitted by this castle is emitted towards the oblique upwards, because the refractive index on the path is constantly decreasing, so as a whole, the light is bent, protruding outwards, and finally at the highest point, it meets the requirements of total reflection, directly changes the direction, comes diagonally downward, and finally enters the human eye.
At this time, for ourselves, because the direction of the eyes is above the distant sea surface, although the actual castle position is more backward and lower, we will still think that we see the castle above the sea surface, replaced by the object of this event, that is, we see part of the fish-shaped Pingzhou Island on the distant sea.
In fact, the above situation belongs to the mirage of the upper present, and the mirage that appears on the general desert belongs to the lower mirage, as for the mirage of the side, its cause is also the temperature difference (it can also be said that the difference in atmospheric density), but this difference is reflected in the horizontal direction, not in the height direction.
Thus a mirage is a natural phenomenon that has been reasonably explained (has nothing to do with the parallel universe, etc.), and its original scenery is an object that exists on Earth.
In addition, the number of mirages in places such as Penglai in Shandong and Huilai in Guangdong is relatively large and famous.
#海市蜃楼 #