Navigation menu Show  Figure 1. The proton-proton fusion process that is the source of energy from the Sun.[1] The energy from the Sun - both heat and light energy - originates from a nuclear fusion process that is occurring inside the core of the Sun. The specific type of fusion that occurs inside of the Sun is known as proton-proton fusion.[2] Inside the Sun, this process begins with protons (which is simply a lone hydrogen nucleus) and through a series of steps, these protons fuse together and are turned into helium. This fusion process occurs inside the core of the Sun, and the transformation results in a release of energy that keeps the sun hot. The resulting energy is radiated out from the core of the Sun and moves across the solar system.[3] It is important to note that the core is the only part of the Sun that produces any significant amount of heat through fusion (it contributes about 99%).[3] The rest of the Sun is heated by energy transferred outward from the core. StepsThe overall process of proton-proton fusion within the Sun can be broken down into several simple steps. A visual representation of this process is shown in Figure 1. The steps are:[4]
The final helium-4 atom has less mass than the original 4 protons that came together (see E=mc2). Because of this, their combination results in an excess of energy being released in the form of heat and light that exits the Sun, given by the mass-energy equivalence. To exit the Sun, this energy must travel through many layers to the photosphere before it can actually emerge into space as sunlight. Since this proton-proton chain happens frequently - 9.2 x 1037 times per second - there is a significant release of energy.[3] Of all of the mass that undergoes this fusion process, only about 0.7% of it is turned into energy. Although this seems like a small amount of mass, this is equal to 4.26 million metric tonnes of matter being converted to energy per second.[3] Using the mass-energy equivalence, we find that this 4.26 million metric tonnes of matter is equal to about 3.8 x 1026 joules of energy released per second! For Further ReadingFor more information on the energy that comes from the Sun, see:
References
The Sun and Nuclear Fusion"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the Universe to do." ~ Galileo Mass: 1.989x1030 kg Radius: 695,000 km (equator) Mean Density: 1.410 gm/cm3 Rotation Period: 25 - 36 days Escape Velocity: 618.02 km/sec Luminosity: 3.839 x 1026 watts Magnitude (Vo): -26.8 Surface Temp: 5,780 K (mean) Age: 4.5 billion years In the core of the Sun hydrogen is being converted into helium. This is called nuclear fusion. It takes four hydrogen atoms to fuse into each helium atom. During the process some of the mass is converted into energy. Mass of 4 H atoms: 4.03130 AMU The difference between the mass of 4 H atoms and 1 He atom is 0.02862 AMU which is only 0.71% of the original mass. This small fraction of the mass is converted into energy. If 4 grams (1/8 ounce) of H are converted to He, only 2.8x10-3 grams of the mass is converted to energy: How much energy is generated from converting such a tiny amount of mass? We can calculate by using Einstein's famous formula. E = mc2 Enough energy to keep a 60-watt light bulb shining for over 100 years! The Sun has different layers with different properties, these layers are composed of material that is about 75% hydrogen and 25% helium by mass. Simply put, the Sun is a great ball of gas, hot enough to glow in every tier. In the very innermost part of the Sun, called its core, the temperature is about 15 million Kelvins, the density is 150 times that of water, and the pressure is over 200 billion times greater than atmospheric pressure here on Earth. This heavy, sweltering place is where the Sun's energy is produced via a process known as thermonuclear fusion. While fusion is difficult to mimic on Earth, the core of the Sun and other stars is a perfect environment for it. Here, the temperatures are high enough for hydrogen nuclei to smash together and form helium nuclei, releasing tremendous amounts of energy in various forms. Energy produced in the form of light keeps bouncing around inside the Sun, as though the Sun were made entirely of mirrors. A particle of light can take more than 30,000 years to reach the surface and escape! Energy in the form of small particles called neutrinos, however, can travel directly out of the Sun and into the Solar System. Neutrino observatories on Earth measure the continual wash of these tiny, fast-moving particles. The apparent visual magnitude of the Sun is -26.8, making it appear about 10 billion (10,000,000,000) times as bright as the next brightest star, Sirius. The absolute magnitude of the Sun, the magnitude it would have at a distance of 10 parsec or 32.6 light years, is +4.8. Among the brightest stars we can see with the naked eye, there is only one, alpha Centauri, with a comparable absolute magnitude to the Sun. Most of the rest are intrinsically far brighter. Light takes about 500 seconds (8 1/3 minutes) to travel from the Sun to the Earth. The average distance to the Earth from the center of the Sun is about 149,000,000 km, or 93,000,000 miles; a distance known as an astronomical unit (AU). There are over 63,000 AU in 1 light year. 1 AU is about 0.000016 light year. The nearest star, alpha Centauri, is 4.3 light years distant, or about 280,000 AU. Activity on the solar surface, photo by Brad Snowder. Where does the Sun's fusion occur?This fusion process occurs inside the core of the Sun, and the transformation results in a release of energy that keeps the sun hot. The resulting energy is radiated out from the core of the Sun and moves across the solar system.
What stage of fusion is our sun?Like most stars in our universe, the Sun is on the main sequence stage of its life. This means nuclear fusion reactions in its core fused hydrogen into helium.
Which layer of the Sun has enough heat and pressure for fusion to occur?The Core: The core is the power generator in the Sun. The core radius is close to one-fourth of that of the star. Inside the core, pressures and temperatures are high enough to make fusion.
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In what layer of the Sun does fusion occur?
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