4. Describe the three (3) main layers of the Sun's interior.
The three (3) main layers of the Sun’s interior are the Core, Radiation Zone, and Convection Core. First, the Sun’s Core or innermost part, is tightly packed and with a temperature of about 1.5x107 K. It extends from the Sun’s center to the photosphere (that is, approximately 0.25 solar radius or 1.75x105 km). It is at the Sun’s Core that thermonuclear reactions occur because of the enormous temperature and pressures. Second, the Sun’s Radiation Zone or the middle interior part, where energy travels as photons and then becomes gamma, surrounds the Core and extends up to the Convection Zone. The temperature in this radiative zone drops to about 7.0x106 K to 2.0x106 K. Third, the Convection Zone or the outermost portion of the Sun’s interior, is where turbulent convective plasma motions occur. The convective zone has a hotness of approximately 1.0x106 K .
11. What do astronomers mean by a "model of the Sun"?
Astronomers refer to a “model of the Sun” to “describe how energy escapes from the Sun’s core” . It is an astronomical description and mathematical equations of the interior parts of the sun’s model. The model depicts the sun’s luminosity, density, temperature, mass, pressures, length of each layer, and so on.
15. What is a neutrino, and why are astronomers so interested in detecting neutrinos from the Sun?
A neutrino, or tiny neutral one, is a chargeless (i.e., electrically neutral) and “originally believed to be massless” (close to zero mass) subatomic particle with half-integral spin . Neutrinos have three flavors: tau, muon, and electron. Aside from travelling at approximately the speed of light, they rarely react with normal matters. Neutrinos that float around came about nearly 1.5x109 years ago. Additionally, they originate out of violent astronomical events such as solar explosions. Astronomers are so interested in detecting neutrinos from the Sun because they escape from the solar core and serve to back up fusion reaction theory concerning sun’s longevity .
1. Stellar parallax measurements are used in astronomy to determine which of the following properties of stars? a. speeds, b. rotation rates c. distances, d. colors, e. temperatures .
[“Stellar parallax is the most accurate means of measuring distances to the starts” . Parallax measurement only works on stars with relative closeness to the Earth (that is, by a couple of thousand light-years). Beyond such distances, contemporary instruments will not be able to measure a parallax that too small. Hence, astrophysicists employ some other indirect techniques beyond a couple of thousand light years. These techniques include stellar motion, interstellar lines, inverse-square law, and period luminosity relation.]
11. Briefly describe how you would determine the absolute magnitude of a nearby star.
26. What is the mass-luminosity relation? To what kind of stars does it apply?
Mass-luminosity relation refers to the association between stellar mass and intrinsic brightness (luminosity); hence, “the more massive a star, the more luminous it is” . In equation form, L/L = (M/M)a, where L, L, M, M, and a (which equals 3.5) are the stellar luminosity, mass, and main-sequence stars. The mass/luminosity relationship applies to main-sequence stars and not to white dwarfs, red giants, neutron stars, or other non-main sequence stars.
2. What is the lowest mass that a star can have on the main sequence? a. There is no lower limit, b. 0.003 Me, c. 0.08 M, d. 0.4 Me, e.2.0 M.
(“The lowest-mass main-sequence stars  have masses between 0.08M and 0.4M” . Generically, these stars are known as the red dwarf stars. Red dwarf stars are relatively cooler because they burn their fuel much slower. Their size are also too small, that is, much smaller than half the Sun’s size or nearly 1.0x102 times planet Jupiter’s size.)
9. On what grounds are astronomers able to say that the Sun has about 5 billion years remaining in its main sequence stage?
Astronomers are able to state that the Sun “should remain  for another” 5.0x109 years remaining in its main-sequence stage because they were able to compute remaining hydrogen left in it . Through the use of theoretical models and astrophysical knowledge about the evolution of stars, astronomers are able to calculate the amount of hydrogen that is consumed inside the Sun’s core. They also factor in luminosity, size, magnitude, etc. of the Sun to arrive at such an approximation.
11. How is the evolution of a main-sequence star with less than 0.4 M fundamentally different from that of a main-sequence star with more than 0.4 M?
The evolution of a main-sequence star with <0.4 M is fundamentally different from that of a main-sequence star with >0.4 M in terms of fusion reactions. The former converts all its mass to helium, then “fusion in the core drastically slows down” . For a main-sequence star having <0.4 M, hydrogen fusion inside its core stops when its hydrogen content is nearly used up; what is left is pure hydrogen at the core, which becomes surrounded with a shell for hydrogen fusion to continue. Because of shell fusion, more helium is added to the core, making the star to contract even more thereby becoming hotter in the process. The exterior atmosphere expands tremendously for a star to turn into a giant.
2. A white dwarf is composed of primarily a. neutrons, b. hydrogen and helium, c. iron, d. cosmic rays, e. carbon and oxygen.
(Usually, white dwarf stars consist of “carbon and oxygen,” which is the products of the ultimate fusion of medium-sized stars . A white dwarf’s compositional state is too compressed caused by its electrons’ degeneracy. The star’s electrons are kept apart by quantum force resulting from Pauli’s exclusion principle. An interesting trivia about these stellar corpses is the fact that if they are more massive, the tinier they become. White dwarf stars have too slow energy lost to become black dwarf stars. Our universe is still too young to have made black stars. Although there are billions of years old white dwarfs that were already identified, having hotness under 4.0x103 K, they are still not black stars. As white dwarf stars cool, they change from plasma into “giant crystals” . Other partially crystallized stars of this type have already been identified.
8. What is the Chandrasekhar limit?
Chandrasekhar limit refers to the theoretically possible upper mass limit, equivalent to 1.4 solar mass or approximately 3.0x1030 kg., for a stable white dwarf star or neutron star. If it is greater than that limit, a collapsing star will turn into a black hole or neutron stars. Stars having a mass less than the Chandrasekhar limit prevent themselves from collapsing because of their electrons’ degeneracy pressures, where there is sudden failure “to support the star’s enormous weight” for the core to collapse . (Degeneracy pressures refer to quantum effects, under Pauli’s exclusion principle, that only two electrons or fermions can occupy either a spin up and down at a given energy state and not both at the same energy level and spin. It was named after an Indian-born American astrophysicist Subrahmanyan Chandrasekhar by W. Anderson and E. Stoner, a German-Estonian astrophysicist and a British theoretical physicist, respectively. In other words, the maximum mass white dwarf stars can possibly have prior to becoming a supernova is also known as the Chandrasekhar limit. As mentioned in the above paragraph, the value is about 1.4 solar mass or approximately 1.4 times our Sun’s mass. However, other factors should also be considered such as the white dwarf star’s spin, composition, and so on.
10. Compare a white dwarf and a neutron star. Which of these stellar corpses is more common? Why?
A white dwarf star emanates from a smaller star whereas a neutron star originated from bigger star. White dwarf stars are more common stellar corpses because they are lower mass stars. White dwarfs are results of main-sequence stars while neutron stars are results of more massive main-sequence stars. In addition, white dwarfs are composed of degenerative matters; thus, do not generate energy using nuclear fusion. On the contrary, neutron stars, as the name states, consist mostly of neutron particles and also do not generate energy using nuclear fusion. Moreover, white dwarf stars have less than 1.4 solar mass whereas neutron stars have 1.4 to 3 solar masses. White dwarfs are small and dense, yet neutron stars are much denser and rarer than the former. Further, white dwarf stars are located at the center of nebulae while neutron stars are close to supernovae remnants .
2. Supermassive black holes are found in which of the following locations? a. in the centers of galaxies, b. in globular clusters, c. in open (or galactic) clusters' d. between galaxies, e. in orbit with a single star .
(A supermassive black hole, at the center of a galaxy, is called an active galaxy’s nucleus. The nucleus of a galaxy shows intense radiations such as x-ray, infrared, radio, and optical wherein it exhibits intense jet of magnetic energy and particles emanating from a supermassive black hole’s center. Supermassive black holes power the active nucleus. The accreting dust and gas are bright especially in the electromagnetic spectrum’s infrared and optical regions.)
6. If the Sun suddenly became a black hole, how would Earth's orbit be affected?
The Earth’s orbit will not be affected even if the Sun suddenly became a black hole because it will be a negligible change, except for the radiation or light that push itself. The orbit of the Earth would be left unchanged because the Sun, as it turned out to be a black hole, would have the same mass as before. Hence, same mass means same gravitational pull. In other words, if a sols (that is, solar mass) black hole would replace suddenly our Sun, the planetary orbits would not be altered. The reason is that physical laws determine the planetary orbital motions, which include our planet in the solar system. Thus, it all depends on the Sun’s actual mass – no more and no less than that – and whether or not the gravitational attractions between the Sun and planets is within it (the Sun) or at its substitute (black hole). Lastly, by Hawking the process, “the mass of a black hole  eventually disappears” .
Comins, N. F. and W. J. Kaufmann. Discovering the Universe. New York: W. H. Freeman, 2011. Web.