Why can't most mirages be traced back to their original scenes? Don't they exist in real life?

As the weather gets hotter, mirages are appearing more and more frequently in some places, such as Qingdao - it was rumored online that a mirage appeared again yesterday evening.

At around 5:15 p.m., Mr. Liu, a citizen of Qingdao, saw three obvious mountains in the sea area south of the Haitian Center where ships were entering and leaving. There should be no mountains in this direction, so he recorded the scene with his camera (as shown below).

Mirage picture, source: Mr. Liu

The scene under normal circumstances, source: Mr. Liu

However, judging from the photos, the mirage scene (three mountains) recorded by Mr. Liu is not particularly clear. This may be because it occurred late, the light was not strong, and the sky was cloudy, which were not good conditions for the formation of a mirage, so the mirage is blurry.

However, when I looked at the comments section, it seemed that more people were concerned about why every time a mirage appears, the original scene in reality cannot be found. Many people doubt whether mirages really exist in real life.

Of course, the original scene in the mirage must be real, because it is different from an illusion. Instead, the light reflected by the real object actually enters our eyes, so you can take a picture of it.

However, it is not easy for us to find the original scene in the mirage. This is caused by many factors. We have to start with the formation of the mirage.

What is a virtual image?

We know that a mirage is a virtual image and it is not where we see it.

The virtual image can be seen by the eyes, but it cannot be displayed on the light screen, or the light does not really reach the place where the image is formed, which is consistent with the illusory nature of a mirage.

When light rays diverge and cannot form an intersection, they cannot form a real image or be displayed on a light screen. However, when these divergent rays enter our eyes, our eyes can see an image at the intersection of the reverse extension lines of the divergent rays. This is a virtual image.

A simple example is an object in a mirror. When the light from the object is reflected by the mirror, it is divergent, and these scattered light rays are collected by the eye, so a virtual image appears in the mirror, which is not the real position of the object.

In fact, the virtual image defined in physics looks quite complicated, but we can simply understand it as a visual illusion. The position of the object only corresponds to the perception of our eyes, and our eyes cannot feel the refraction of light. The eyes only think that the light is still propagating along a straight line. This is why virtual images are formed on the reverse extension line of the light.

Once you understand the virtual image, it will be easy to understand the imaging principle of the mirage.

The mirage is caused by the light reflected by objects being refracted through the air and accidentally entering the human eye. Eventually, our eyes see scenery somewhere else in front of us. This process is exactly the same as when we see fish through water.

The light reflected by the fish (real object) is refracted when it leaves the water, and these refracted rays are collected by our eyes. In the end, the fish we see is a virtual image that is farther away and shallower.

However, the refraction of a mirage is much more complicated than this, because it does not simply undergo a single refraction.

How does light travel in a mirage?

When light propagates in different media, it will be refracted. However, our air is not always evenly distributed. It will change due to various reasons, which ultimately leads to different air densities in different regions or at different altitudes. This is the premise for the formation of mirages.

We have said before that mirages are most likely to appear in summer. The reason is that the hotter it is, the easier it is to create different temperature gradients, thus forming different air density gradients.

In addition, mirages appear most frequently on the sea surface and in the desert. The reason is that the surfaces of these two materials are very easy to create different temperature gradients, but they are at different altitudes.

When the sun shines on the sea, it heats the atmosphere above the ocean. Due to the cooling effect of the sea water, the temperature is lower near the ocean and higher up the sea, the temperature becomes higher.

Due to thermal expansion and contraction, the air density will appear "thin at the top and dense at the bottom", which will form a light refractive index gradient.

Now, there is an object in front of our eyes that reflects light to the surroundings. After passing through the "thin top and dense bottom" air, it will be refracted downward layer by layer and enter our eyes.

However, our eyes still believe that light travels in a straight line, so the mirages that appear on the sea surface are generally high and appear to be suspended. This is called a superior mirage.

The opposite of what happens on the sea surface occurs in the desert; the sand has a low specific heat capacity, so it heats up quickly, causing the temperature near the surface to be higher than that far from the ground.

The end result is that the light from the object is refracted upward and enters the eye. At this time, the virtual image seen by our eyes is downward, which is called an inferior mirage.

If the object is close to the ground at this time, we will see a mirage similar to the reflection on the water surface, so mirages related to water sources are often seen in the desert.

Similarly, sometimes temperature gradients also appear in the horizontal direction, and at this time we may see side views, which is called a side mirage.

Why is it so difficult to find the original scene of a mirage?

We often see mirages appearing somewhere, but we cannot find the original scene.

In fact, from the formation of mirages and the propagation of light in this process, it is not difficult to find that it is not easy to find the original scene of the mirage.

Man-made mirage, source: Shy halatzi

First of all, the most common mirages are caused by air convection creating different air densities, which ultimately achieve different refractive index gradients and send light to our eyes.

Air convection is similar to shaking water. It is very unstable and it is difficult for us to fully see the true appearance of the mirage, let alone find it.

Secondly, the perspective of the mirage is not necessarily the same as when we normally look at the scenery. For some objects, different angles mean two different objects.

Because mirages enter our eyes through the refraction of light, it is difficult to determine exactly where we are seeing it, or where we need to look to get the same view as in the mirage.

Image source: Brocken Inaglory

at last

Mirages are actually not a rare phenomenon, and can even be seen everywhere in summer.

In the summer, if you often drive on asphalt roads, you may see that it seems like water appears on the asphalt road. This is actually a mirage phenomenon.

This process is the same as that which causes mirages to form in the desert, since asphalt roads are made of similar material to sand.

Source: Guai Luo WeChat Official Account