People always say that "the heart is higher than the sky", how high is the sky? Why is the sky blue?
From ancient times to the present, we are full of fantasies about the sky above our heads, dreaming of one day being able to go up to the sky to see. Looking up at the sky overhead, it is often blue, especially after the rain, it is even clearer. So, what exactly do we see in this blue sky? Why is it blue?
In fact, the sky we see is the Earth's atmosphere, from the bottom to the top are the troposphere, stratosphere, ozone layer, mesosphere, thermal layer and diffusion layer, if further outward to extraterrestrial space. The atmosphere is thick, with an average thickness of 1,000 km. In terms of altitude, the closest stratosphere to the ground is about 10,000 meters, and some transnational airliners fly in the troposphere. So, how high is the sky? At least 10,000 meters or more.
In fact, the atmosphere itself has no color, so why is the sky we see blue? Is it because of the color of the sea? In fact, it is not, the blue color of the atmosphere is due to the combination of atmospheric molecules, ice crystals, water droplets, etc. in the atmosphere and sunlight. As introduced in the middle school textbook, sunlight through the prism can be divided into red, orange, yellow, green, blue, blue and purple light of different colors, the wavelengths of these seven kinds of light are different, and the ability to penetrate the earth's atmosphere is also different.
It is important to know that there are many particles in the atmosphere, and the air is also composed of tiny gas molecules. The vast majority of these nitrogen and oxygen, as well as carbon dioxide and industrial exhaust, are very small but still hinder the flow of light from the sun to the ground. Sunlight in the process of passing through the atmosphere, like red light and infrared, the wavelength is very long, can easily break through the layers of the atmosphere to reach the ground. However, like purple, blue, and cyan light, the wavelength of these lights is relatively short, and it is easy to be stopped by particles and scattered during the process of passing through the atmosphere. These scattered purple, blue, and cyan lights will remain, so that the sky we can see will take on the blue color it is now. After heavy rain, particles other than air molecules in the air are washed away, making the sky look cleaner and bluer.
Do you know how high a bird can fly? Can they fly into the atmosphere?
Mount Everest is more than 8,800 meters above sea level, which is close to the troposphere, and the tallest building built by humans is the Burj Khalifa in Dubai, which cost billions of dollars to build and is only 828 meters high. Animals are much more powerful than humans.
Unexpectedly, birds like sparrows and hummingbirds can fly up to 5,000 meters, and even wild ducks can leap more than 6,000 meters. Spotted geese flew at a height of 7,290 meters, and in 1974, an airplane flying at an altitude of 11,278 meters crashed into a Central African vulture. In fact, migratory birds such as geese and swallows can often fly to an altitude of 3,000 to 4,000 meters during migration.
You know, the higher the altitude, the less the air, the lower the temperature, and the lower the oxygen content at high altitude, why don't birds have "altitude sickness" and can fly freely at high altitude? Over the course of thousands of years of evolution, birds have gradually adapted to the high-altitude environment.
Some people who live in the plains go up to the plateau or high altitude, and they are prone to altitude sickness, and some even need to absorb oxygen. But birds don't have these problems, and in the high air, spotted geese can increase their breathing rate and inhale more oxygen. And the birds don't stay in the sky all the time, they're more like roller coasters, high and low. So sometimes, a lot of people like migratory birds and vultures, they're already flying in the atmosphere. So why do birds fly so high? There are two main reasons, coolness and few natural enemies. During long-distance flights, it is inevitable that it will overheat, and the high-altitude and low-temperature environment can make the migration process of birds more comfortable. And few predators can fly that high, and birds are safer.
Do you know how far the satellite is from the ground? Are all satellites in extraterrestrial space?
In nature, some migratory birds can fly to the troposphere or even the stratosphere. As the top representatives of human technology, we enjoy the convenience brought to us by satellites all the time. So do you know how high the satellite is from the ground?
If you divide all the satellites according to the level of orbit. It can be roughly divided into low-orbit satellites, medium-orbit satellites, high-orbit satellites, geostationary orbit satellites, geostationary orbit satellites, sunsynchron-orbit satellites, large elliptical orbit satellites and polar orbit satellites. As the name suggests, the low-orbit satellites are the closest to the ground, about 150 to 200 kilometers of altitude, and here is still the atmosphere, so the satellites operating here are experiencing the erosion of atmospheric particles all the time, and the life span is only 7 to 21 days.
What many people don't know is that except for some high-orbit satellites, such as resource exploration satellites, agricultural satellites, and meteorological satellites, most of these operate in the atmosphere. Most of the communication satellites operate in extraterrestrial space or at the edge of the atmosphere, because the impact of the atmosphere here is small and does not hinder communication, such as the beidou satellite system on the mainland and the GPS satellite in the United States. There are a total of 24 GPS satellites in the United States, and the average orbital altitude of these satellites is more than 20,000 kilometers. Among the satellites that make up China's Beidou navigation system, there are 5 geostationary orbit satellites that are fixed in orbit 36,000 kilometers above the ground, and there are 30 medium and high orbit satellites, which have an altitude of more than 21,000 kilometers.
So, when we look up at the sky, maybe there are birds flying there, and there are satellites made by humans.