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| The Milky Way |
1. The energy of ionization is 13.6 eV. Using the conversion factor between eV and ergs, this corresponds to 2.18 x 10-11 ergs.
3. Nebulae has densities of 100-1000 atoms per cubic centimeter, which is comparable to the best vacuums possible on Earth. The solar wind has a density of several particles per cubic centimeter.
5. This is a trick question, to some degree. It is not that the metal content causes the elongated orbit. It is that the same thing that causes the low metal content is responsible for the elongated orbit. In this case, it is that Pop II stars formed in such a way that they have both elongated orbits out of the galactic plane and low metal content (because they are so old). This is a specific example of a general fallacy that one must guard against in scientific reasoning: If A and B are both caused by C, it may appear that A causes B when in reality they are unrelated except through the root cause C.
7. Assuming the Sun to be 5 billion years old and the time for the Sun to move once around the galaxy is about 250 million years, the number of times it has been around is about (5 billion / 0.250 billion) ~ 20 times.
9. Dust both lowers the apparent magnitude (extinction) and reddens its color (reddening) because it preferentially scatters blue light.
11. The gas density is much lower in the ISM than in the star's photosphere, so collisional broading should be much less in the ISM. Thus, lines produced by absorption in the intervening interstellar medium would be much sharper than those produced in the star.
13. Radio frequency observations can penetrate the dust. They show that there are galaxies in the part of the sky called the "zone of avoidance" just like in every other direction.
15. Extinction near the Sun is about two magnitudes for each thousand parsecs; from the distance-magnitude formula, the distance modulus is m - M = 10 for a distance of 1000 pc. But the light will appear to be two magnitudes dimmer, so the distance modulus will seem to be 12, which corresponds to a distance of 2512 pc. So we would estimate a distance of 2512 pc, but it is really 1000 pc when corrected for dust extinction.