Although the sun is as hot as 6000°C, the heat decays with distance.
Secondly, if there is heat absorption, there will be heat loss. The earth does not roast because it is in the heat balance.
The transfer methods of heat transfer are mainly divided into three types:
- Heat conduction: Heat transfer relies on direct contact with objects, while the Earth is "suspended" in a vacuum.
- Thermal convection: The flow of fluids carries away heat, and the Earth's atmosphere is actually lost very slowly.
- Thermal radiation: Any object with temperature radiates heat through electromagnetic waves.
So the heat loss on Earth, the first two are extremely low, mainly released to the universe through thermal radiation.
The reason why most people can intuitively know that the sun is continuously releasing heat, and they cannot feel that the earth is releasing heat, is essentially because of visible light.
Earth life is born to the sun, and the heat of sunlight is always the most sensitive to our eyes.
Capturing the temperature of sunlight with your eyes is the instinct of most animals.
But in fact, the temperature span in the universe, from 0K to billions of billions of K, the visible light segment that our eyes can see is only a very narrow area.
The visible light segment is mainly electromagnetic waves released by hundreds of K~10,000 K objects.
In the universe, the main object with this temperature range is precisely - stars.
Human beings can only see the spectrum of the sun, and all this has long been clearly arranged by evolution.
Although we can't see the earth glowing light, just as our body is constantly releasing infrared rays, the earth is also constantly "glowing", mainly radiating infrared rays to the universe and releasing its own heat.
If there is no sunlight, the temperature of the earth will be very low.
There are two main sources of heat in the Earth's interior.
- 1. It released 4.6 billion years, and when it was formed in the early days, the heat energy converted by gravitational potential energy accounted for 20%.
- 2. There are uranium-238, uranium-235, thorium-232 and potassium-40 in the earth's interior, which are constantly decaying and exothermic, accounting for 80%.
The total power of the earth's internal heat is: 4.42×10^13W
The Earth's surface area is about 510 million square kilometers, and the power per unit area is:
0.866W/m2。
That is, if there is no sunlight, the earth's unit area will slowly release heat at a power of 0.866W.
Thermal radiation is calculated by the Stefan-Boltzmann law.
j∗=vT4
- ε is the radiation coefficient, the black body is 1, and the earth is not completely black, the value is 0.97
- δ is the Stefan-Boltzmann constant, with a value of 5.67×10−8W/m2· K4
- Τ is the thermodynamic temperature
At extremely low temperatures, there will be no gaseous atmosphere on Earth, air and water will form a thick layer of ice, forming a snowball Earth, without the atmosphere as a down jacket, heat is directly released into the universe. The presence of a large amount of ice on the surface is also the reason for the emission coefficient of 0.97.
Obtained:
T=j∗/εδ4=63K
That is, if there is no sun, the temperature of the surface is only about -210 °C.
What would happen if we suddenly added solar radiation to the Earth at this point?
The solar constant is 1367W/m2.
Solar constant – the amount of solar radiation received per second per unit area perpendicular to the sun's rays at the apex of the atmosphere.
At this time, the sunlight directly hits the ground, and through the previous radiation formula, we can find that the temperature of the direct solar surface heat equilibrium is as high as:
397K
That is, 124 °C, more than 100 °C.
The reason why the temperature will not continue to rise is precisely because at this temperature, the heat released by the earth to the universe has reached 1367W/m2. No more heat to heat it up.
At this time, the earth is actually like a purgatory world, regardless of rotation, the maximum temperature in one hemisphere is as high as more than 100 degrees Celsius, and the lowest temperature in the other hemisphere is as low as minus 200 degrees Celsius.
This temperature difference is actually very similar to the state of the moon. Considering the reflection of light by the snowball Earth, the temperature will actually be lower.
However, as the temperature rises, the solid oxygen and nitrogen vaporize again into the atmosphere, and the earth wears a thick down jacket.
At the same time, it will melt into the ocean, and the high specific heat capacity of the sea water allows him to absorb enough heat during the day so that the surface is not too hot. Heat is released at night so that the surface is not too cold. Coupled with the flow of the atmosphere, the rotation of the earth reduces the temperature difference between day and night on the surface.
For any circle, the cross-sectional area is 1/4 of the surface area.
Then, when the atmosphere is not considered, the average surface temperature is:
280K
That is, only 7°C.
The presence of the Earth's atmosphere and oceans also reflects 34% of sunlight.
In this way, the average temperature is even as low as 253K.
That is, temperatures as low as -20°C.
But the average temperature of the Earth is 14°C.
Why is the calculated temperature a full 34°C lower than the actual temperature? Where does the extra calories come from?
The difference is so big precisely because of the warmth of the down jacket on the earth.
Excess heat, which is essentially the heat radiated out by the earth, is absorbed by the atmosphere and counterradiated back again. And it can retain heat relatively durably through repeated reverse radiation.
The hot and sweltering summer weather is mainly due to atmospheric inverse radiation caused by thick clouds.
In short, the earth is like a man in a down jacket who roasts a fire in winter.
He has his own body temperature (geothermal heat), but this amount of heat is too little relative to absolute zero.
So he also needs to bake the fire (solar radiation), if you directly bake the fire like this, the temperature of the roasted side will be too high, and the temperature of the unbaked side will be too low.
So he kept spinning to share the heat, and then put on a thick down jacket (atmospheric).
This down jacket is indispensable to the thermal balance of the earth today.
The earth has been absorbing solar energy, and the reason why energy is conserved is that the earth is constantly radiating heat like the sun. Other reasons are the position of the specific equilibrium temperature.
This article is original by Zhanyun, welcome to pay attention and take you to long knowledge together!