We see the stars shining, not because the luminosity of the stars has changed, but because of the occlusion of the atmosphere.

The atmosphere is between us and the stars. When starlight passes through the atmosphere, it will be affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency will change according to its density. So when we look at the stars through it on the ground, we will see that the stars seem to be flashing.

2. Why do people yawn?

When we feel tired, a lot of carbon dioxide has been produced in our bodies. When there is too much carbon dioxide, oxygen must be supplemented to balance the needs of the body. Because these residual carbon dioxide will affect our body's functional activities, then the body will send out a protective reaction, so we yawn.

Yawning is a deep breathing action, which will let us breathe in more oxygen and expel more carbon dioxide than usual, and it can also eliminate fatigue.

3. Why can snakes walk without feet?

Snakes have many scales, which are the outermost armor on their bodies. Scales are not only used to protect the body, but also to be their "feet".

When a snake crawls forward, its body will be S-shaped. Every scale outside the S-shape will tilt upward to help the snake catch the uneven road when it moves forward. These scales cooperate with the muscles of the snake and can push the body forward, so the snake can walk without feet!

4. Why do sunflowers always bloom towards the sun?

There is a substance called "auxin" in the stem under the sunflower disk. This substance has the function of accelerating replication, but it is anti-optical, and it will run to the backlight side whenever it encounters light.

So when the sun rises, the stem of the sunflower immediately hides to the side of the backlight, as if the whole plant is bent in the direction of the sun.

5. Why does hair turn white when people are old?

There is a substance called melanin in our hair. The more melanin, the darker our hair will be. Without melanin, hair will turn yellow or white. When human beings reach old age, various functions of the body will gradually decline, and the formation of pigments will be less and less, so the hair will gradually turn white!

6. Why do fireflies glow?

Fireflies emit light because there is a luminous body at the end of their abdomen, which is filled with a lot of phosphorus-containing luminescent substances and luminescent enzymes, so that fireflies can emit flashing light.

The purpose of fireflies is not only lighting, but also courtship, vigilance and trapping. This is also a communication tool for them. Different kinds of fireflies emit light in different ways, frequencies and colors, so they can convey different information.

7. Why do you growl when you are hungry?

When you are hungry, you will purr. This is because the food you have eaten before has almost been digested. Although the stomach is empty, the gastric juice in the stomach will continue to secrete. At this time, the contraction of the stomach will gradually expand, and the liquid and gas inside will be stirred up and purr.

Don't be embarrassed by your stomach growling next time! Because this is a normal physiological action.

8. Why can't ostriches fly?

A giant ostrich, but they can't fly into the sky! This is not because their wings are useless, but because their feathers are too soft and their wings are too small to fly at all. In addition, the ostrich's muscles are underdeveloped and its sternum is flat, which is not conducive to flying.

Ostriches live in Africa. Because they have lived in desert areas for a long time, their bodies gradually evolved into what they are now in order to adapt to the environment.

9. Why can't it go bad easily?

Lunch meat, black beans and ketchup beans are all delicious canned foods, which can be preserved for a long time and are not easy to deteriorate. This is because the can is sealed, so bacteria can't enter.

When people make canned food, they pump all the air out of the canned food and then seal it. In the absence of air, even if the food inside is contaminated with a little bacteria, they can't survive or reproduce!

10. Why does the baby cry all the time when it is born?

Babies cry when they are born, not because they are unhappy, but because they are taking the first breath of air!

When babies leave their mother's body and are born, the first breath of air will rush to their throats, violently impact the vocal cords, make them vibrate, and then make a sound similar to crying.

1 1. Why do lizards keep bouncing up after their tails are broken?

In order to protect themselves, many lizards also protect their eyes and ears; When some lizards are attacked, their tails will be broken due to the severe contraction of their muscles. Because there are still some nerves alive in the broken tail, it will keep bouncing, thus distracting the enemy and running away. Don't think that their lives will end like this. In fact, it only takes a few months, and their tails will grow back and move on.

12. Why is the squirrel's tail so big?

Don't look at the relaxed mouse tail! When the squirrel jumps around the tree, its tail plays a great role. It can keep balance when the squirrel jumps to the tree to avoid falling and being injured. In addition, this big tail can play a more protective role in winter, tightly surrounding the squirrel's body, which is convenient and practical.

13. Why can't a person have one or three thumbs?

The average person has five fingers, each with a different length. However, does anyone realize that besides the thumb, other fingers also have three sections, while the thumb alone has only two sections? It turns out that the number of joints is just the same as the other four fingers. If it is three knots, the thumb will appear weak, so that it can't lift heavy objects; If there is only one section, it can't grasp things freely with the other four fingers!

14. Why don't you scratch yourself?

When others scratch ourselves, we will feel itchy and laugh constantly; However, when we scratch ourselves, we not only don't laugh, but also don't itch. Based on our psychological preparation, the brain will send out a message that there is no danger, and the nerves will relax, so that they will not laugh and itch!

15. Why are most seawater blue and green?

Looking at the sea, it is often found that the sea water is blue-green. However, when you pick up the sea water, you can only see it as transparent and colorless as old water. It turns out that the seawater itself is not much different from the water we touch every day, and it is also transparent. The green we see is actually a phenomenon caused by the ability of seawater to absorb light. Only green light can be absorbed and reflected by seawater; When the seawater is deep, the green light is also absorbed, and the seawater looks blue.

16. Why do you get goose bumps?

Hair grows on the surface of our skin, and there is a vertical hair muscle under each pore. When stimulated by nerve (such as anger, fear, cold, etc. ), the body temperature will drop, the vertical hair muscles will contract, making the hair stand up and form goose bumps. In addition to keeping warm, this physiological system can make animals look bigger than they really are, thus scaring off enemies.

17. The hippocampus was born in dad's stomach?

Almost all animals are females, but the hippocampus is different. It's male. On the belly of the male hippocampus, there is an incubator similar to a kangaroo "pouch", and the female hippocampus will discharge the eggs into the incubator of the male hippocampus. Since then, the male hippocampus has assumed the responsibility of pregnancy. In about three weeks, the little sea horse will pop out of his father's body.

18. Why do leaves change color?

The reason why leaves change color is related to the chemical substance chlorophyll. When autumn comes, the days are shorter and the temperature is lower than that in summer, so the leaves stop producing chlorophyll, and the remaining nutrients are transported to the trunk and roots for storage. Leaves lack green chlorophyll and other chemical pigments appear at the same time, so we often see yellow and brown leaves.

19. Why are there leaves?

It's fall here. Leaves evaporate more water than in summer, but roots absorb less water than in summer. In order to reduce the water loss of trees, stem cells began to form separation layers. When the nutrients leave the leaves completely, the separation layer separates the leaves from the trunk and leaves fall off.

20. Why do whales spray water?

A whale is a mammal, but its nose has no shell, and its nostrils grow on the top of its head. Living in water and breathing with the lungs can store a lot of air at a time, and you don't need to breathe on the surface often. But when it breathes to the surface, it breathes through its nose. When it breathes, the huge sound waves emitted by the sea water are caused by pressure.