This paper focuses on howthe sun produces heat and light and how that energy is absorbed by the Earth.Multiple layers of hot gas make up the entirety of the sun; the layers of thesun that will be discussed include the photosphere, the chromosphere, thecorona, and the core. The core is the area where the most important nuclearreaction takes place via a proton-proton chain reaction, where the sun turnsmass into energy. This mass-to-energy conversion can be described by one of themost famous equations in science, E=mc2.
Radiation is the sun’s mainway of getting this energy to the Earth. Most of the solar radiation receivedis actually absorbed by the Earth, but some of it is reflected back into space.What is absorbed and how much is absorbed in different areas of the Earthdepends on the angle of the rays of the sun; the more slanted the angles, theless concentrated sunlight there is, resulting in cooler temperatures.Radiative equilibrium can occur when incoming solar energy matches outgoingheat energy, allowing for a relatively stable global temperature. Without thesun, this temperature would decrease rapidly and continue to decrease until theEarth was a frozen ball of nothingness.
However, the sun does not look like itis going anywhere any time soon, and thank gravity for that. All stars are able to create energybecause they are all, essentially, just massive fusion reactions (Cain). Wejust happen to be in the perfect spot to receive the sun’s abundance of energy;this spot is what is known as the sun’s Habitable Zone (Williams).
Getting thatenergy from the sun to the Earth is not as simple as it sounds, as there aremany layers of the sun and different processes that must occur in order forsolar energy to get where it needs to go. As stated in the above paragraph, thesun is composed of multiple layers. The region that we are able to see is whatis known as the photosphere. Temperatures in the photosphere range from about4500 K to 7500 K (Smith), though the upper part of the photosphere is actuallycooler than the lower part. Because of this, a phenomenon known as limbdarkening occurs causing the sun to appear brighter in the center (Cain). It isalso in this layer where the energy from the sun is released to us as heat andlight. The chromosphere is above thephotosphere, ranging from 5000 K to upwards of 100,000 K; this part of the sunis visible to us only when a solar eclipse occurs, which is also true for thecorona. The corona lies above the chromosphere, reaching temperatures of up toa boiling 2,000,000 K (Smith).
Sunspots are darker and cooler areasthat appear in the photosphere and can vary in size, reaching up to 50,000kilometers in diameter (University of California). The abundance of sunspots isrelated to the brightness of the sun; the brighter the sun, the more sunspotsthat appear. According to the University of California, San Diego, “it has todo with changes in the magnetic field of the sun and with convection within theouter layer of our star (not with processes in the core).” Solar flares arealso produced in the photosphere and can produce bursts of ultravioletradiation and electromagnetic radiation (Sharp). Radiation is the primary way the sun’senergy travels across space to reach the Earth’s atmosphere. According to theOhio State University, “about 43 percent of the total radiant energy emittedfrom the sun is in visible parts of the spectrum.
” The upper layer of theatmosphere of the Earth filters most of the sun’s ultraviolet radiation,however, what passes through is absorbed by the Earth, and, in return, is whatheats our planet (Ohio State University). The average amount of solarradiation that is absorbed by the Earth is 70 percent, which means that 30percent of that is reflected back into space. The intensity of this solarradiation is largely due to the angle that the sun’s rays strike the Earth(Ohio State University). At the equator, for example, the intensity is constantbecause the angle of the rays is more concentrated, whereas in the North andSouth poles, the angle of the rays is more slant, thus dispersing more of thesunlight.
Other factors that make certain areas colder or hotter than others dependupon the concentration of air molecules and small particles in the atmosphere.At higher latitudes, the sun’s path is longer, so there will be more airmolecules and small particles for the sunlight to travel through, resulting inless solar energy reaching certain areas (Yung). Earth will reach radiativeequilibrium when the flow of incoming solar energy is equal to the flow ofoutgoing heat energy, resulting in a relatively stable global temperature. (OhioState University). We know that the sun and the Earthwork together to sustain life and that the sun’s light and heat energy travelsthrough the Earth’s atmosphere and gets absorbed by the Earth, but how exactlydoes the sun, alone, come up with all of its energy? The sun is just a hugeball of hot gas, most of which is hydrogen, making up about 70 percent of thesun. The sun is also constantly turning this hydrogen into helium through aprocess called nuclear fusion (Cool Cosmos).
This process is able to take placebecause of just how hot and how much pressure resides in the core of the sun. Themost important nuclear reaction in a brightstar is the carbon-nitrogen cycle. However, since our sun is more of dimstar, it uses the proton-proton chain reaction instead (Hong Kong Observatory). The process begins with a protonthat fuses with another, and then transforms into a neutron by way of theweaker nuclear force. As the neutron is formed, so is a positron and a neutrino;this pairing between the positron and the neutrino is known as a deuterium.
Then, a third proton collides with the deuterium, resulting in a helium-3nucleus and a gamma ray. The gamma ray works its way from the core to the outerregions of the sun and is released as sunlight. After the formation of twohelium-3 nuclei, they will collide with one another to create a helium-4nucleus.
This helium-4 nucleus contains less mass than the original fourprotons that came together, thus resulting in an excess amount of energy beingreleased in the form of heat and light. According to Energy Education, “of allthe mass that undergoes this fusion process, only about 0.7% of it is turnedinto energy.” That may seem like a miniscule amount of mass, but it is equal to4.26 million metric tons that are being converted into energy every second(Hanania). This mass-to-energy conversion canbe described by the formula E=mc2, where E is the kinetic energy ofa body, m is the mass, and c2 is the speed of light squared.
Thisequation states that mass and energy are, effectively, the same thing. Theenergy created by the nuclear fusion process exerts outward pressure, andunless it is contained, the pressure will result in an explosion. What keeps astar (or our sun) from exploding is the gravitational attraction of the gasmantle surrounding the core (University of California). What keeps us and our planet aliveis the sun and its heat and light energy that it so “willingly” provides forus. We can only imagine what would happen if the sun were to disappear.
To saythe least, life on Earth would look very sad indeed; it has been theorized thattemperatures would drop rapidly, and the atmosphere itself would freeze,”leaving us exposed to the harsh radiation travelling through space”(O’Callaghan). Thankfully, we should not have to worry about that in ourlifetime.