Introduction
Solar energy, which includes both heat and light, is the driving force behind different processes taking place on planet Earth. More specifically, solar energy fuels the life-supporting biological processes that take place in plants, which in turn act as the primary source of food for most animals and human beings. On the other hand, solar energy in form of heat supports various processes within the Earth’s surface including generating winds and initiating the movement of ocean currents. Moreover, the sun’s energy plays a major role in maintaining the Earth’s temperatures; hence, determining climatic changes across different parts of the world (National Aeronautics and Space Administration [NASA], 2014). Therefore, it is important to examine how the sun generates its energy and transfers it to the Earth’s surface. This essay seeks to highlight the major processes involved in solar energy production with specific emphasis on the major components of the solar system and the nuclear fusion reactions that take place within the core of the solar system.
The Structure of the Sun
Before explaining how the sun produces light and heat, it is important to look at the major components of the solar system. The figure below provides an overview of the major parts of the solar system, which include the solar core, the radiative zone, the convective zone, the photosphere, the chromosphere, and the corona among others.
The figure above shows that the core of the solar system is the innermost part, and it covers about 1.5 percent of the sun’s volume. Moreover, the core of the solar system represents almost 50 percent of the sun’s mass (NASA, 2014). At any given moment, the temperature of the solar core can reach up to 15 million degrees Kelvin, and its pressure level can rise to almost 134 g/cm3, which is over 250 billion times the pressure of the atmospheric surface of the Earth (Bruckner, 2013). The major composition of the solar core includes protons, nuclei, neutrons, and free electrons (NASA, 2014). Several nuclear fusion reactions involving hydrogen atoms and helium atoms take place within the core of the solar system, and most of these reactions release energy, which escapes the sun’s core through other adjacent layers (NASA, 2014; Pelton, 2013).
The radiative zone of the solar system comes immediately after the core, and its temperature is relatively lower, estimated at approximately three million degrees Celsius (Bruckner, 2013). Moreover, the density and pressure levels of the radiative zone are relatively lower than the conditions that occur within the solar core. Furthermore, the radiative layer comprises hydrogen and helium nuclei as well as free electrons (NASA, 2014). On the other hand, the third part of the solar structure is the convection layer, which occurs approximately 150,000 kilometers away from the sun’s surface. Within this layer, temperatures are much lower, estimated at approximately one million degrees Kelvin (Bruckner, 2013). Moreover, within the convection layer, nuclei exist in close association with electrons and most atoms are undamaged or in gaseous form (NASA, 2014). The other important layer of the solar structure is the photosphere, which is the visible or the outermost part of the sun, and it extends several kilometers away from the other parts because of its gaseous nature (NASA, 2014).
The Generation of Sunlight and Solar Heat
Albert Einstein is credited for developing the earliest model that explains the processes through which the sun produces light and heat. According to Einstein’s model, it is possible to convert mass into energy (McCracken & Stott, 2012). Subsequently, other scientists including Francis Aston discovered precise ways of measuring atomic masses; hence, it was possible to determine the number of hydrogen atoms that represented the mass of one helium atom (McCracken & Stott, 2012). More specifically, Francis Aston discovered that the size of one helium atom is slightly smaller than the size of four hydrogen atoms (McCracken & Stott, 2012). Accordingly, other scientists including Arthur Eddington used Aston’s model to determine how the sun produces energy through nuclear fusion reactions involving the combination of several hydrogen atoms to form one helium atom (Bruckner, 2013). Nonetheless, the above-mentioned models did not explain how nuclear fusion took place within the sun considering that the principles of classical physics dictate that nuclear fusion reactions must take place under extremely high temperatures (McCracken & Stott, 2012).
The solutions to the problems concerning the above-mentioned models came after the emergence of the scientific subfield of quantum mechanics. The establishment of quantum mechanics enabled scientists to understand the principles of physics that governed nuclear fusion reactions. More specifically, following the development of quantum mechanics, many physicists began to question the processes behind the formation of heavier elements from much lighter ones. Accordingly, it was later proposed that the fusion of a given number of hydrogen atoms could result in the formation of a single helium atom. Moreover, different nuclear reaction experiments in the laboratory enabled various nuclear physicists to discover how the fusion of three helium atoms could form a single carbon atom; subsequently, the physicists concluded that it was possible to fuse lighter elements to form heavier ones (McCracken & Stott, 2012).
Accordingly, the most widely accepted theory that explains the sun’s ability to generate light and heat involves the nuclear fusion of several hydrogen atoms to form a single helium atom. This reaction generates a lot of energy, which escapes from the core of the sun through the radiative layer to the convective layer, the photosphere, and finally to the Earth’s surface (Lang, 2008). However, note that the fusion of hydrogen atoms to form a single helium atom is only the beginning of a series of complex reactions within the core of the solar structure. According to NASA (2014), the process of generating solar energy involves the fusion of the nuclei of hydrogen atoms to form the nuclei of a helium atom. Unlike chemical reactions, which involve the interaction of electrons, reactions that involve the fusion of nuclei require large amounts of energy (Lang, 2008). Hence, the sun’s ability to fuse the nuclei of different hydrogen atoms depends on the availability of extremely large amounts of energy.
The core of the solar system has enough energy to drive the nuclear fusion of hydrogen nuclei to form a helium nucleus. The high temperature within the core of the solar system supports the breakdown of hydrogen atoms into their constituents which include hydrogen nuclei (protons) and electrons that possess a negative charge (NASA, 2014). In order to form a single, positively charged helium nucleus, which contains two protons and two neutrons, there must be a fusion between the masses of two hydrogen nuclei (Lang, 2008). This reaction occurs as shown in the following equation:
Proton + Proton = Deuteron + Positron + Neutrino
Source: NASA, 2014.
From the above reaction, note that the two protons arise from two different hydrogen atoms and the deuteron comprises one proton and a neutron. The neutron arises from the destruction of the mass of one of the hydrogen nuclei (proton) during the reaction (NASA, 2014). On the other hand, the proton that is converted into a neutron loses its positive charge, which eventually goes to the positron. Lastly, the presence of the uncharged neutrino counters the movement of the position within the core of the sun (NASA, 2014).
The energy required to fuse two protons comes from the high amount of heat and pressure that exists within the core of the solar system. Under such circumstances, it is possible for photons to interact with a deuteron, and in the process give rise to a helium-3 nucleus as shown in the following equation:
Proton + Deuteron = Helium-3 nucleus
Source: NASA, 2014.
After the formation of the helium-3 nuclei, two of these nuclei fuse to form a helium-4 nucleus and two extra protons as shown below:
Helium-3 nucleus + Helium-3 nucleus = Helium-4 nucleus + Proton + Proton
Source: NASA, 2014.
The subsequent collisions between helium-4 nuclei and protons within the core of the solar system could be the source of many other chemical elements known to man (NASA, 2014; Lang, 2008). Generally, all the nuclear fusion reactions mentioned in the foregoing discussions are major sources of solar energy, which escapes the core of the sun into space, and finally to the Earth’s surface. More specifically, the sun’s light and heat arise from the destruction of the mass of positrons and loose electrons after they collide with each other. In conclusion, the nuclear fusion-based model that explains the processes through which the sun generates energy provides compelling evidence that has stood the test of time.
References
Bruckner, D. (2013). Nuclear fusion – Bringing the sun to earth. Heidelberg, Berlin: GRIN Verlag.
Lang, K. (2008). The sun from space (2nd ed.). Heidelberg, Berlin: Springer-Verlag.
McCracken, G., & Stott, P. (2012). Fusion: The energy of the universe. Waltham, MA: Academic Press.
National Aeronautics and Space Administration [NASA]. (2014). Sunlight and solar heat: How are they made?Jet Propulsion Laboratory, California Institute of Technology. Web.
Pelton, M. (2013). First law of physics, let there be light. Wheaton, IL: Tyndale House Publishers, Inc.