I understand that winter happens because part of the planet gets less sunlight for part of the year due to axial tilt. I also understand that the tropics get more sunlight, while the poles get less. I understand that planets that are further from the sun are often colder, and those closer to the sun are warmer.
What I don’t fully understand is how the planet can cool off after it’s already warm. It’s in space; there’s nothing for the molecules to rub against. That’s why spaceships need radiators to cool off. So, once it’s hot, wouldn’t it stay hot forever? I vaguely remember something as a child about infrared radiation escaping the atmosphere, but I’m really not sure how heat turns into light like that, nor am I fully convinced that would even be efficient enough to chill the planet that quickly, but I could easily be wrong.
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The planet is emitting energy in the form of lower energy photons.
Sun energy in, lower energy photons out.
Everything in balance, as it should be.
Warm objects constantly radiate energy in the form of black body radiation. Basically the atmosphere passively radiates heat outward just like a radiator on a space ship. So you’ve always got heat leaving, but most of the heat enters through the part of the world where it’s summer.
Are you asking how heat escapes the atmosphere?
Heat escapes because heat is energy transfers from one body to another as the result of a difference in temperature. Heat IS the energy, it doesn’t transform into radiation, it leaves through the radiation.
Also, other heat that’s in the air rises until… it leaves.
Same reason it gets cold at night, the Earth radiates heat into space. The ground, buildings, pretty much everything is emitting some amount of heat as infrared light.
When the ground warms up it can then radiate infrared radiation and this can pass through the atmosphere and into space, cooling the planet, some gases in the atmosphere can reduce the amount of radiation passing through the atmosphere trapping the infrared radiation like a greenhouse, the balance of these gases determines if the planet cools down or heats up.
Heat, or more accurately energy, can transfer in many ways, molecules rubbing together is only one of them. The type of heat transfer in space is called radiation and it uses electromagnetic waves to do so. The idea of cooling as you’re thinking is convection, which is when fluids (air/gasses are considered fluids) move around to disperse heat. The last is conduction, which is when heat transfers between two things directly touching each other. Heat always wants to travel from higher temperature to lower, and space is very very cold.
The planet is the radiator. This is a consequence of the Stephan-Boltzmann Law, that anything with a temperature will radiate. That includes frying pans, people, planets, black holes.
The physical mechanism? Temperature means that the molecules are vibrating, electrons are excited. These can go to lower energy states, which emits photons. These travel away and carry energy.
As for how this would cool off a planet enough, that’s a state of equilibrium. Energy loss from radiation increases with temperature (mathematically, proportional to temperature to the fourth power). The Earth more or less gains energy from the sun and loses it to space. At one extreme, if the Earth is at absolute zero, it loses no energy but gains energy from the sun, so its temperature would increase. At another extreme, if the Earth is at the sun’s temperature, it cannot gain more energy from the sun passively, so it loses net energy via radiation. There is some temperature in between where the energy gained from the sun equals the energy loss from radiation, on average.
The planet is a radiator. It’s in equilibrium and radiates off as much energy as it receives from the sun. If it didn’t, it would keep getting hotter and hotter.
The thing that changes is how much heat the surface, oceans and atmosphere holds onto. Like a buffer that can vary in size. Change the amount of greenhouse gasses, or change the reflectivity, and the amount of heat being held in the buffer increases or decreases until equilibrium is reached again.
Heat, energy, radiation, light… they’re all sides of the same coin. It’s all electromagnetic radiation. Heat is just on a wavelength you can’t see… but thermal cameras can.
The planet is a big thing, like really big. It’s made up of water, rock, air, organic material, a molten core, it’s blanketed by an atmosphere which reaches hundreds of kilometres into space, gradually thinning out.
The sun is ALWAYS applying energy. Luckily for the earth, it rotates in day night cycles, and the axis shift provides seasons on its hemispheres.
Because the heat source moves around constantly, because the planet spins, because the vast atmosphere of skies heat up and generate winds, because tidal forces and heat generate huge currents in the seas, the heat continually mixes.
The heat from the sun mixes with winds and moves around the planet, creating warmer nights and cooler days. It is absorbed in water and carried through the oceans, it creates water vapour which traps heat as potential energy in thick clouds. Plants store it as food and extracted carbon. Some of it escapes the atmosphere as infra red radiation
How does the planet get colder? Well it does and it doesn’t. It’s a messy harmony of processes that mix, conserve, use and release energy. This results in weather patterns that produce cold areas and warm areas. The planet as a whole isn’t getting particularly colder or warmer. (ignoring global warming, which is a separate issue of humans messing with this harmony and causing a shift in how energy is managed)
Your correct, Earth produces thermal radiation and thus sheds its heat to the universe through thermal radiation. Basically, everything composing matter that isn’t at 0 K moves, and this movement gets converted to electromagnetic radiation which scapes main body, taking a bit of energy with it.
Your intuition on it not being enough is incorrect, however, as Earth has achieved a balance, which by definition means it’s sufficient. There’s a term for it, energy budget. It’s true that if the earth had greater energy credit it’d get hotter, up to a limit as bodies emit this heat proportional to their temperature, so the hotter it is the more it releases, prevent infinite loops.