The process at which the Sun creates energy begins with hydrogen nuclei which are individual protons. Four protons are needed to make one helium nucleus. It begins with two protons that fuse and create a deuterium nucleus. The creation of the deuterium nucleus equals to one proton and one neutron, then two protons that have just created the one proton and one neutron will add another proton to the mix. We now have a nucleus of helium-3 made up of two proton (which use to be three) and one neutron. You will need two sets of these helium-3 to come together to form helium-4. If we go back to the beginning of forming the neutron, it actually takes four protons to start the process of turning those four protons to start the process of turning those four protons into helium-4. Helium-4 is ultimately made up with two proton and two neutrons, remembering it takes four protons to make one proton and one neutron. The reason this whole process creates energy is because the mass of a helium nucleus is a hair less than the combined mass of four hydrogen nuclei. In the process of being fused together, a little bit of mass is lost. This whole fusion reaction that is taking place can only happen if the protons come close enough together for an effect known a quantum tunneling (Bennett, Donahue, Schneider & Voit, 2012, p.292-293).
Gravitational equilibrium is a balance of forces. A gravity force that is pulling inward as another force of gravity is pushing outward. To be able to keep the Sun's core temperature and fusion rate steady, you need gravitational equilibrium along with energy balance. If the output of energy from the Sun fluctuated Earth would not be a fun place to live. It may burn us up one minute but the freeze us the next. Fortunately the Sun does not fluctuate but stays very steady. With gravitational equilibrium is the Sun's core temperature rises or drops it will help the Sun to get back on track by allowing the core of the Sun to shrink or expand to allow the cooling off or heating up of the core. The photosphere looks bright and dark. The bright orange spots of all different shapes and sizes is the hot gases of the Sun rising. In between all these bright orange spot you also have dark orange streaks, lines, and curved of the cooler gases sinking back into the photosphere. Because of underlying convection, this is what makes the hot gases rise and fall and give its photosphere surface a look of granulation. Photons are rising out of the hot gasses providing sunlight to all the planets in orbit. The hot spots, or shades of black, you would see in photos are actually cooler than the rest of the photosphere areas, and because it is cooler it will show up in photos of the Sun as darker areas. The hottest gases flow much easier than cooler gases. You would think that since the sun spots are cooler the hotter gases surrounding that spot would flow right in and mix it all up, but it does not, there is something keeping these cooler areas from mixing in with the rest. Magnetic fields are doing just this. Magnetic fields can alter atoms and ions causing these dark areas to spit into two causing these sun spots to create arches filled with magnetic energy, these arches are also helping the processes of keeping these sun spots a cooler temperature. Eventually the magnetic field will become weak allowing the hotter gases to flow back in and mix everything up to the same temperature (Bennett, Donahue, Schneider & Voit, 2012, p.294-297).
We can study the stars by measuring different stellar luminosities. Some stars are very far away and seem brighter than even the closest star to us. We can use the apparent brightness of the star and the luminosity of the star to find out more about its place in our universe and how hot it is really burning. Luminosity is a measure of a stars power and the apparent brightness is a measure of power per unit area meaning the amount of starlight reaching Earth per second per square. Other than the apparent brightness and luminosity, another important factor is the surface temperature of a star. The surface temperatures are put into classes of spectral types. The spectral type is important when identifying stars because it tells us what the hottest stars are and what the coolest stars are. It even maps out at what point a star is in its lifeline. It would be like looking at a photo of human beings of all different cycles in our life from conception to death. The hottest star which also has the bluest colors are called spectral type O. Spectral type O is the highest in the class and all others decline from here following the declining surface temperatures. OBAFGKM is the classes of spectral types (Oh Be A Fine Girl/Guy Kiss Me). The coolest stars are situated on the last letter of the spectral pattern as M. The have the coolest surface temperatures of as low a 3000 K and they burn a red color. The cool, red stars are much more common that the hot, blue stars. A few examples of the spectral types G-M are our Sun, Eridani, Cygni, Lacaille, Gliese A & B. Some of the B-F star types include Achernar, Vega, Sirius, and Altair, in this class we call these start the super giants. Some O types of stars on the spectral pattern are Centauri and Spica. The mass of a star is defiantly more difficult to measure out of all the things that we could measure in a start because we can only determine the masses by using Kepler's third law; we can only use the third law in binary star systems. This is a system in which two stars continuously orbit each other, and by using Kepler's third law we can measure both their orbital period and the separation in between them. They can also establish masses of many other different stars by observations of eclipsing binaries (Bennett, Donahue, Schneider & Voit, 2012, p.309-314).
Our Sun falls into the main sequence class being a G2, a little lower than what is classified as the middle of the spectrum. The Sun will stay a main sequence star for most of its lifetime. When it starts to change it will move up the line of spectrums someday becoming a giant and a super giant during the end of its life. Eventually it will end up being a white dwarf that is no longer on the lifeline of the Hertzsprung-Russell (H-R) diagram. Our sun will last such a long time because lower mass stars tend to exhaust their nuclear fuel on a steadier basic than higher mass stars which tend to exhaust the nuclear fuel quickly (Bennett, Donahue, Schneider & Voit, 2012, p.320-321). As we had talked about earlier our Sun is the perfect star for life to be created among the planets that orbit it. Our Sun is a very low mass star and therefore the process of nuclear fusion will go on for a long time or about 10 billion years. You would not want to live around a high mass star as it burns their nuclear fusion at a very high rate and they would not last a 10 billion year lifespan. For life to be created on a planet orbiting a star you need billions of years to help the process. Look at our human development, we have been created but it has taken billions of years for us to evolve to that point, and hopefully humanity will last for a few billion of years before we fade out in time.
References:
Bennett, J., Donahue, M., Schneider, N. & Voit, M. (2012) The essential cosmic perspective. (6th ed.) San
Francisco, CA: Pearson Addison-Wesley
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