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How is energy transported to light up the light bulb in your room? Well, depending on the source of energy, it may go something like this.
First, giant machines dig through the ground to dig up coal. That coal, an energy source, is dumped into trucks or railcars. Then it's taken to a coal plant where its energy is converted into electricity. This then travels via wires to your home to light up that light bulb. There are clearly lots of steps involved in what seems like a simple task: flipping the switch.
How energy is transported in the Sun to light up the Earth, to eventually give someone the simple pleasure of warmth on their skin on a cool day, will be explained in this lesson.
The Radiative Zone
The temperature of the Sun, the surface of the Sun to be exact, is 5800 Kelvin. Compare that to the temperature at the center of the Sun, about 16 million Kelvin. You know that heat always flows from hot areas to cool areas. Thus, heat from this incredibly hot center of the Sun moves towards its cooler surface and from there, into space.
The extremely hot center of the Sun is its core, where it generates its energy through nuclear fusion. Because it's so hot over there, gamma ray photons are found at its center. Photons are bundles of electromagnetic radiation. Short-wavelength, high-energy photons, like gamma rays, are emitted at higher temperatures than longer-wavelength, lower-energy photons.
From the core, these high-energy gamma ray photons will not travel straight out into space. If that happened, they'd escape into space two seconds after being emitted. Such a quick exit from the core is not possible because the gamma rays will be deflected and scattered every which way by electrons and atomic nuclei located at the core. Think of it as one gigantic and awfully long-lasting bumper car match where the photons try to escape the rink, but the electrons and nuclei constantly bump the photons in random directions.
But with time, the gamma ray photons will make their way outwards, towards the cooler areas of the Sun. As they do so, their high energy will be converted into several photons of lower energy, like a high-value currency can be converted into several units of a lower-value currency.
The outward motion of this energy from the core occurs in the form of radiative diffusion, and thus, astronomers refer to one of the inner parts of the Sun nearest the core as the radiative zone, the area inside a star, like the Sun, where energy flows outwards as photons, which remember, are little packets of electromagnetic radiation.
In the process of radiative diffusion, photons are emitted in one place and absorbed in another, thereby transporting energy between two points.
The Convective Zone
In this way, the energy flowing outwards from the core as radiation will eventually get to more outer layers of the Sun. Here, as you already know, the gas is cooler. This lower temperature means the gas here isn't completely ionized. For us, this means that such a layer of gas isn't really transparent to radiation.
Like you can't see through an opaque window, energy can't get past an opaque gas very well. Therefore, the energy flowing outwards from the Sun's interior will get backed up as if behind a dam.
Have you ever seen a water wave hit a sea wall? You probably saw how it began to churn after it impacted that wall. Well, imagine the waves of energy flowing outwards from the interior of the Sun hitting more opaque, cooler gas; that's like a sea wall. With nowhere to really go, this energy will begin to churn using the process of convection.
Convection means hot gas will rise while cool gas will sink in a circular motion in the convective (or convection) zone, the region inside a star where energy flows outwards using the process of convection. For us, this means energy is no longer flowing outwards as photons but rather as rising and falling currents of gas.
From there, when the energy reaches the visible glowing surface of the Sun, the photosphere, it will be radiated out into space as photons, including those of visible light. Consequently, instead of taking two seconds to exit into space, it will take energy generated at the center of the Sun hundreds of thousands or even millions of years to escape due to everything we've discussed in this lesson.
And what did we discuss? We discussed the radiative zone, where gamma ray photons are bumped around in a random fashion, thereby slowing their escape into space. And we also discussed the convective zone of the Sun, where energy hits a cool, opaque, gaseous wall of sorts, slowing the escape of energy into space as well.
Photons are bundles of electromagnetic radiation and the radiative diffusion carrying the Sun's energy from the core occurs in the radiative zone, the area inside a star, like the Sun, where energy flows outwards as photons.
As the energy flows outwards, it encounters cooler, opaque gas, which isn't very transparent to radiation. The energy backs up and is transported outwards as rising and falling currents of gas in the convective zone.
The convective (or convection) zone is the region inside a star where energy flows outwards using the process of convection. From there, when the energy reaches the visible glowing surface of the Sun, the photosphere, it will be radiated out into space.
When you are done with this lesson, assess your ability to:
- Highlight the processes that take place in the sun's radiative zone
- Explain the way in which energy escapes the radiative zone
- Discuss the fact that the convective zone serves as a dam for energy from the sun's interior
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