We see twinkling of stars not due to a change in brightness of stars themselves, but due to occlusion of atmosphere. The atmosphere is between us and stars. As starlight travels through atmosphere, it is affected by density and thickness of atmosphere. The atmosphere is not absolutely transparent, its transparency depends on density.
So when we look at stars through it on ground, we see stars appear to twinkle.
Why do sunflowers always bloom towards sun?
The part of stem below disk of a sunflower contains a substance called auxin. This substance has function of accelerating reproduction, but it has an anti-rotation property: every time it encounters light, it goes to side that is not lit.
Therefore, when sun rises, sunflower stem immediately hides on illuminated side, and it seems that whole plant leans towards sun.
Why do fireflies glow?
Fireflies will glow because they have a light emitter at end of their abdomen, filled with a variety of phosphor luminescent substances and luminescent enzymes, so that fireflies can emit flashes of light. The purpose of light of fireflies is not only for illumination, but also for courtship, warning, trapping and other purposes.
It's also a communication tool. Different types of fireflies have different lighting methods, frequency and color of light, and they use this to convey different messages.
Why do squirrels have such big tails?
Don't look at squirrel's tail! While squirrel is jumping up and down tree, its tail is doing a lot of work. He can balance a squirrel while jumping up a tree to avoid falling and getting hurt. In addition, this large tail can play a more protective role in winter by tightly surrounding body of the squirrel, which is convenient and practical.
Why is sea water mostly blue and green?
When looking at sea, I often find that sea water is blue-green. However, when you scoop up sea water, all you see is that it is as clear and colorless as water was in past. It turns out that sea water itself is not much different from water that we come into contact with every day, and it is also transparent.
The green color we see is actually result of sea water's ability to absorb light. Only green light can be absorbed by seawater and reflected; when sea water is deeper, green light is also absorbed and sea water looks blue.
Why do leaves change color?
The reason leaves change color is due to chemical they contain, chlorophyll. When autumn arrives, days are shorter and temperatures are cooler than in summer, so leaves stop producing chlorophyll and remaining nutrients are transported to the trunk and roots for storage.
Leaves lack green chlorophyll, while other chemical pigments appear, so we see more yellow and brown leaves.
Why does sorbet smoke?
Sorbet smokes because there is a lot of invisible water vapor in outside air. When it encounters a very cold sherbet, it turns into mist and surrounds sherbet when it is cold. It seems that sorbet "gassing" "The same.
Why do cicadas shed their skin?
The shell (exoskeleton) of cicada is hard and cannot expand as cicada grows. When cicada grows to a certain stage, cicada's exoskeleton restricts cicada's growth, and cicada removes original exoskeleton, this is cicada's swamp.
How do bees make honey?
The bees first spit sweet juice from plucked flowers into empty hive. At night, they suck sweet juice into their honey stomach to cook it, then spit it out and swallow it again. 100 to 240 times finally into sweet honey.
Why do people yawn?
When we feel tired, body produces a lot of carbon dioxide. When there is too much carbon dioxide, oxygen must be added to balance body's needs. Since this residual carbon dioxide will affect functional activities of our body, at this time body sends a defensive reaction, so we yawn. Yawning is a deep breathing action that allows us to take in more oxygen and exhale carbon dioxide than usual, and also eliminates fatigue.
Why can snakes walk without legs?
Snakes have many scales, which are outer layer of armor on their bodies. The scales are used not only to protect body, but also their "legs". As snake crawls forward, its body takes on an S-shape. Each scale outside of S-shape will be raised to help snake grip rough road as it moves forward. These scales interact with snake's muscles and can push body forward to crawl, so snake can walk without legs!
Why do people get gray hair as they age?
There is a substance in our hair called melanin. The more melanin it contains, darker hair will be. And if there is little melanin, hair will turn yellow or white. When people reach old age, various functions of body gradually decrease, and production of pigment becomes less and less, so hair gradually becomes white!
Why does my stomach growl when I'm hungry?
When you're hungry, you'll grumble. This is because food you ate before is almost overcooked. Although stomach is empty, gastric juices in stomach will continue to flow. At this time, contractions of stomach will gradually expand, and liquid and gas inside will agitate, causing a gurgling sound. Don't be embarrassed that your stomach will growl next time! Because it is a normal physiological action.
Why can't an ostrich fly?
A species of ostrich with a big body, but they can't fly! It's not that their wings don't work, it's that their feathers are too soft and their wings are too small to fly. In addition, ostrich has underdeveloped muscles and a flat sternum, which is not conducive to flight. Ostriches live in Africa. Since they lived in desert areas for a long time, their bodies gradually evolved into what they are today to adapt to environment.
Why doesn't food in a tin go bad?
Breakfast meat, dace in black bean sauce, beans in tomato sauce... all these are delicious canned foods that can be stored for a long time without spoiling. This is because jars are sealed so bacteria cannot get inside. When people make canned food, all air is pumped out of can, and then it is sealed. In absence of air, even if food inside is colored by a small amount of bacteria, they cannot survive or reproduce!
Why do babies cry after birth?
Babies wheeze when they're born, not because they're unhappy, but because they're taking their first big breath of air! When babies are born outside their mother's body, their first breath of air rushes down their throats, hitting their vocal cords hard, causing them to vibrate and make a cry-like sound.
Why does a lizard keep jumping after its tail is torn off?
To protect themselves, many lizards also use a protective covering to hide humans' eyes and ears, and when attacked, some lizards have their tails torn off due to violent muscle contraction. Due to fact that some nerves are still alive in broken tail, it will continuously bounce, thereby distracting enemy so that he can escape. Do not think that their life will end this way, in fact, it only takes a few months for tail to grow back and continue to live.
Why can't a human thumb have one or three joints?
The average person has five fingers, and length of fingers can vary. However, has anyone noticed that, in addition to thumb, other fingers also have three joints, and thumb has only two joints?
It turns out that number of its segments is exactly same as other four fingers. If there are only three joints, thumb will appear weak and will not be able to lift heavy objects; if there is only one joint, it won't be able to interact with other four fingers to grasp objects freely!
Why doesn't it itch when I itch?
When others scratch us, we feel itchy and constantly laugh; however, when we scratch ourselves, not only do we not laugh, but we do not feel itchy either. Based on our mental preparation, brain will send a no-danger message and nerves will relax accordingly, so we won't laugh out loud and scratch ourselves a lot!
Why is sea water mostly blue and green?
When looking at sea, I often find that sea water is blue-green. However, when you scoop up sea water, all you see is that it is as clear and colorless as water was in past. It turns out that sea water itself is not much different from water that we come into contact with every day, and it is also transparent. The green color we see is actually a phenomenon caused by ability of seawater to absorb light. Only green light can be absorbed by seawater and reflected; when sea water is deeper, green light is also absorbed and sea water looks blue.
Why do I get goosebumps?
There are fine hairs on surface of our skin, and under each pore there is a muscle that straightens hairs. It shrinks and makes hair stand up, forming goosebumps. In addition to its role as isolation, this physiological system can also make an animal appear larger than it really is, thus scaring off enemy.
A seahorse born from a father's womb?
Almost all animals also reproduce females, but seahorses are unusual in that they are born males. The male seahorse has an egg-hatching sac on its abdomen that resembles a kangaroo's "brood pouch", and female seahorse releases eggs into male seahorse's hatching sac. The male seahorse then takes over responsibility of breeding, and after about three weeks, a baby seahorse hatches from father's body.
Why do leaves change color?
The reason leaves change color is due to chemical they contain, chlorophyll. When autumn arrives, days are shorter and temperatures are cooler than in summer, so leaves stop producing chlorophyll and remaining nutrients are transported to trunk and roots for storage. The green chlorophyll is missing from leaves, at same time other chemical pigments appear, so we see more yellow and brown leaves.
Why fallen leaves?
When autumn comes, more water evaporates from leaves than in summer, but roots absorb less water than in summer. To reduce tree's water loss, cells of stem begin to form a layer of shedding that insulates leaves from trunk after nutrients have completely left leaves, allowing leaves to fall.
Why do whales vomit up their noses?
The whale is a mammal, but its nose lacks a shell and its nostrils grow on top of its head. Living in water, it breathes with lungs that can store a lot of air at a time, so it doesn't need to go to surface of water often to breathe. But when he comes to surface of water to breathe, he breathes through his nose, and loud sound waves that are emitted from body when breathing are caused by pressure.
How big is Milky Way?
Many and many fixed centers form a huge galaxy, and galaxy in which solar system is located is called Milky Way. The Milky Way is like a large disk, about 80,000 light-years wide and about 12,000 light-years thick at center, with a total of over 1,000 stars.
Why can't I see stars during day?
Because some of sunlight is scattered by gas and dust in atmosphere during day, sky is very brightly lit, and light emitted by sun is very strong, so we cannot see stars.
What celestial bodies are there in solar system?
There are eight planets in solar system. They go in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. In addition, there are many asteroids, comets and meteors in solar system, and there are 2958 officially numbered asteroids. The most famous comet is Halley's Comet.
How high is blue sky?
The "blue sky" is actually Earth's atmosphere. The atmosphere surrounds earth's air, which is divided into 5 layers according to air density, and has a total thickness of 2000-3000 kilometers. But most of air is concentrated from ground below 15 kilometers, and higher you go, thinner air becomes. What a dense atmosphere, how high must be blue sky.
What happened to thunder?
It is a natural phenomenon when negative and positive electricity meet together. When it rains, some clouds in sky are positively charged and some are negatively charged. When two kinds of clouds meet together, they discharge and emit very bright lightning. At same time, they radiate a lot of heat. , due to which surrounding air quickly heats up, expands and makes a loud noise - thunder.
Why can planes fly into sky?
The plane has two wings, like a bird, as well as propellers. Wings can generate lift to keep aircraft in air, and propellers can generate power to push aircraft forward. Therefore, plane can take off into sky like a bird.
Why are bottles filled with water hard to break?
Two identical glass bottles, one empty and other filled with water, are simultaneously thrown from same height onto ground. Which bottle is more likely to break? Generally speaking, heavy bottles are easy to break. However, when bottle is filled with water, water in bottle has a different function, which can reduce deformation of bottle and make bottle less likely to break.
Breaking glass bottles most often occurs due to deformation. When an empty bottle hits ground, ground puts pressure on bottle and bottle deforms from outside to inside and finally shatters. The bottle is filled with water, and since water is incompressible, deformation is reduced, making it less likely that bottle will break. Fill bottle with water and screw cap on tightly so that it does not break.
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