Danielle has taught middle school science and has a doctorate degree in Environmental Health
Introduction: The Many Layers of The Sun
The Sun, in all of its glory, is one beautiful star. Let's imagine we are an energy particle, called a photon, zipping around inside of the Sun. If we crack open the Sun and see its 'insides,' as shown in the diagram, you will notice a series of layers. We have the core, radiation zone, and convection zone. As a photon we first must originate from the Sun's core. At the core, this is the electrical heartbeat for the Sun. In other words, this is the site where reactions are taking place firing off energy that will eventually leave and produce sunlight. Of course we must mention the temperature for each of these layers. At the core, as you might suspect, it is very hot! 15 million degrees Celsius to be chemically correct.
Zooming around as a photon, we must head straight entering the front door of the next layer called the radiation zone. The radiation zone is the site where energy transport occurs. This zone can be characterized as the place where we, the photons, bounce around facilitating the ability for energy to be transported to the outer surface of the Sun. The temperature at the radiation zone ranges from 2 to 7 million degrees Celsius.
Continuing on with our journey, as a photon, our last stop must be the convection zone. At the convection zone this is the outermost layer of the Sun where convection currents occur. The convection currents take us, the photon, to our final destination: which is the outer surface of the Sun. The temperature of this zone is approximately 2 million degrees Celsius.
Radiation Zone: Overview
Recall that the radiation zone is the site where energy transport occurs. This energy is carried by photons. Extending outside of the Sun's core, the radiation zone occupies roughly 45% of the Sun's radius. An illustration of this is shown below. So how does the radiation zone play such a pivotal role in making sure energy, produced from the Sun's core, travels to the outer surface? Great question!
There are different methods that can be used to physically transport energy to the Sun's outer surface. However, one efficient way is through the use of radiation. Gamma radiation is the type of radiation used. The following diagram illustrates what happens to a photon as it travels through the radiation zone.
When a photon enters this zone it travels a small distance before it is absorbed by a particle. Once it is absorbed, it is spitted out or re-emitted causing it to change its direction in a random way. The photon then travels another small distance before being absorbed again by a particle. Once absorbed it is spit out or re-emitted and changes direction, yet again, in a random way. This process of traveling a small distance, being absorbed, re-emitted, and travelling in a random direction continues until the photon reaches the Sun's outer surface.
Because of this process, bouncing from particle to particle, gamma radiation loses energy over time. This is simply due to the fact that the transportation process is very slow. To note how slow this process is, it is estimated that one photon takes more than 170,000 years to travel outside the radiation zone. We can also think of it this way: on average, one photon roughly travels 1 cm every 10 minutes. Now that is what we call one very slow process! In addition to gamma radiation losing energy, it must be noted that the wavelength of the photon also changes. Specifically, it elongates in length due to the slow nature of this process.
A great way to remember this process is to think of this as a person who is very drowsy. That is, we can compare the path followed by photons, who are absorbed and re-emitted, to a person who is so drowsy they take several random steps before making it to their bed for a much needed nap. In other words, the path a photon takes in the radiation zone is quite random, contributing to the length of time it takes for a photon to reach the outer surface.
The Sun is made of distinct layers: a core, radiation zone, and convection zone. Through each layer, energy is transported as a photon from the core to the outer surface. At the radiation zone this is the site where energy is transported in the form of radiation. Occupying 45% of the radius, the radiation zone has a temperature that is roughly 2-7 million degrees Celsius. The path traveled by a photon, in the radiation zone, is random. This is due to the constant absorption and re-emission by particles. This slow transport contributes to a longer wavelength for the photon and loss of energy for gamma radiation. It is estimated that it takes more than 170,000 years for the photon to leave the radiation zone.
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