What is the meaning of "耀" in the Book of Songs? People in the Pre-Qin Dynasty: Firefly, you have successfully attracted my attention!

"In the dark forest, a silver light suddenly appeared in the distance. It was a guardian god, bringing hope and guidance."

This is a plot in the novel "Harry Potter", but it is also a portrayal of us humans. Before the invention of candles and electric lights, when the sun sets and night falls, it means the arrival of darkness. But we who long for light can always find some luminous objects in the dark. There are many interesting stories surrounding this night light phenomenon.

01 Fireflies and "Blue Tears"

Fireflies emit light, which may be the earliest night-light phenomenon noticed by humans. As early as the pre-Qin period in my country, the "Book of Songs" recorded "Ting Tuan (tīng tuǎn) Deer Farm, shining at night", and the "shining" here refers to fireflies. In ancient times, fireflies were given many poetic names such as "flowing fireflies", "night light", and "night candles", and were therefore known as "poetry insects", becoming a source of inspiration for poets in the long night. Du Mu's "Silver candles in autumn light on the cold painting screen, light silk fans fluttering fireflies" is a classic line.

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Fireflies are actually a general term for insects of the family Lampyridae in the order Coleoptera, with more than 2,200 species worldwide. Fireflies glow because of the presence of luciferin and luciferase in their abdomens. Luciferase is a luminescent catalyst, under the action of which luciferin reacts with oxygen to emit fluorescence in the dark.

Interestingly, not only can flying adults glow, but also firefly larvae and even immobile eggs. It is generally believed that fireflies evolved the ability to glow mainly for courtship, but it is likely that they also rely on fluorescence to communicate with companions, warn enemies, and even lure prey.

Compared to glowing fireflies, another type of glowing creature is even more magical, that is the "blue tears" on the seashore. In many coastal areas in southeastern my country, a dreamy fluorescent sea often appears late at night in summer. As the waves beat, the coastline will turn into a dreamy blue fluorescence, as if the sea has left crystal clear tears.

This phenomenon is actually a red tide caused by the massive reproduction of Noctiluca scintillans. Noctiluca scintillans is a single-celled organism of the phylum Dinoflagellate. Just like fireflies, it stores luciferin and luciferase in its organelles. When the seawater is rich in nutrients, Noctiluca scintillans will suddenly reproduce in large numbers and react to the stimulation of the waves to produce light blue cold light. Although this phenomenon is very spectacular and beautiful, the sudden appearance of Noctiluca scintillans is actually an ecological warning from the ocean to humans, which means that the local seawater is eutrophic and the marine environment has undergone abnormal changes.

The phenomenon of organisms emitting light themselves, such as fireflies and Noctiluca, is called "biofluorescence". In nature, many other organisms can also emit biofluorescence, such as fungi, crustaceans, insects, squid, jellyfish and bacteria.

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The fluorescent sticks we played with as children actually imitate the principle of bioluminescence. Two chemical substances are placed in a plastic tube. Once they are mixed, a chemical reaction will occur to emit light. Now, some scientists are also trying to transplant luciferin and luciferase into some plants. In this way, when we visit botanical gardens at night in the future, we can see dreamy scenes like the science fiction movie "Avatar".

02 Will-O-Wisp is not mysterious

Of course, it is not only living things that emit night light in nature, there are other possibilities. In ancient times, due to the limited level of scientific knowledge, the ancients could not explain many phenomena, and "wisp of the night" was one of them. In a pitch-dark environment, a faint light appeared in the mass grave in the distance, and the light flickered and moved around. This phenomenon of will-o'-the-wisp has been recorded in many ancient books in China and abroad, and has become a classic plot in many folk ghost stories.

For modern people, after mastering basic chemical knowledge, it is not difficult to explain the phenomenon of will-o'-the-wipes. The human body contains about 60 elements, among which calcium phosphate composed of calcium and phosphorus is the main component of bones. After death, under the action of microorganisms, the calcium phosphate in the bones will gradually decompose into calcium phosphide, which will further react with water to produce phosphine. The ignition point of phosphine is only 38°C, so once enough phosphine accumulates, it will easily spontaneously combust in a high temperature environment, thus forming will-o'-the-wipes.

Nowadays, with the reform of funeral methods in our country and the implementation of cremation, the situation where people see ghost lights in the wild has become less and less common.

03 The Night Pearl in the Real World

In folklore and tomb-robbing notes, there is another luminous body that is rarer than the will-o'-the-wisp, that is the night-shining pearl. It is said that the night-shining pearl is a rare gemstone, which was called "suizhu", "xuanzhu", "chuiji", "mingyuezhu" and so on in ancient times. It can glow in the dark by itself, and within a hundred steps at night, it can illuminate every hair, and even prevent corpses from rotting. It is said that after the death of Empress Dowager Cixi, she had a night-shining pearl in her mouth.

In fact, from a scientific point of view, night-shining pearls are a type of mineral with luminescence, and they are not that rare. Although there is no clear definition of what a night-shining pearl is, there is a relatively general consensus in the industry: "If it is produced in nature and can emit phosphorescence for more than 0.5 hours in the dark after being exposed to sunlight, incandescent lamps or other light sources at room temperature for a period of time, and an object with a diameter of 5mm can be seen clearly within a range of 0.33m with the help of this light source, it is called a luminous stone. If it is polished into a spherical shape, it is called a night-shining pearl, and if it is in the shape of a jade disk, it is called a night-shining disk."

Why do gemstones like Night Pearls appear? In fact, the main component of many Night Pearls is fluorite, which is a very common mineral from volcanic rocks and is also the main source of hydrogen fluoride in industry.

Fluorite has a characteristic that the free electrons inside it will enter a high energy state from a low energy state under the stimulation of external energy, just like charging a battery. When the external energy stimulation stops, the electrons will enter a low energy state from a high energy state, and this process will emit light, just like a battery is discharging. So when fluorite is placed under a fluorescent lamp or sunlight, it will glow. However, the light of fluorite is very weak and is almost invisible to our naked eyes under strong light, but it is very obvious in a dark environment.

Of course, the luminescence of fluorite is related to its own texture. Not all fluorites can emit light, and night-shining pearls are not made of only fluorite. In addition to fluorite, diamonds, apatite, scheelite, opal, etc. can also emit night light.

Today, the "Night Pearls" on the market are even more diverse. Many merchants sell "Night Pearls" crafts with artificial strontium boroaluminate (sī). This substance contains rare earth elements and has a similar luminescence principle to fluorite, but with even better luminescence effect. It was the advent of this gemstone, which was only patented in 2003, that completely dethroned the "Night Pearls". Today, we can even buy a good-looking Night Pearl on an e-commerce platform for just a few dozen yuan.

04 Glowing Bones

When these elements undergo radioactive decay, they release energy and emit light. In history, when humans discovered and understood that radioactive elements emit light, there was a tragic story...

The element radium was discovered and named by Marie Curie in 1898. When it was first discovered, radium was regarded as a magical chemical. After scientists found that radium could fight cancerous tumors, the public's worship of radium almost reached a crazy level. From toothpaste and lipstick to milk, bread, and chocolate, all commodities at that time liked to add radium to advertise "health".

Since radium produces ionizing radiation when it decays, thus producing a luminous effect, radium was used as "luminous paint" to draw numbers on watches at that time. In the United States in the 1920s, luminous watches became a popular fashion at the time. Many factories hired young female workers to paint luminous dials. They also had a special name "radium girls". These girls were exposed to large doses and high concentrations of radium every day, but the company did not tell them that radium was a dangerous radioactive element, and even encouraged them to use their lips to hold the tip of the paint containing radium to paint. Soon after, many female workers became ill and eventually died. What is even more shocking is that even after their death, the radium accumulated in their bodies still caused their remains to emit a strange glow.

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Obviously, the luminous light emitted by this radioactive substance is very dangerous and we need to be vigilant. But fortunately, in our daily lives, it is not easy to come into contact with this radioactive element. The paint on the dial of the luminous watch we wear today has also been replaced with a safer isotope of hydrogen - tritium (chuān), which only releases electrons during decay and does not penetrate the human body, and the radiation dose is also negligible. Some manufacturers also use luminous materials such as artificial strontium boroaluminate, which is even safer.

In fact, behind the phenomenon of night light is our process of constantly discovering and understanding the magical nature. This curiosity about the unknown once drove our ancestors to leave the caves and pursue the light in the darkness, and it also inspires us today to use the phenomenon of night light to create more possibilities for life and the world.

Source: Chongqing Science and Technology Museum

Author: Quasimodo in the Garden, Science Popularizer

Audit expert: Li Chunli

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