CHAPTER 4 Review & Discussion:

1. A continuous spectrum is a ``rainbow'' like that produced by a white light bulb. An absorption spectrum is a continuous spectrum with dark lines appearing at certain wavelengths, so that certain colors are missing from the spectrum. An emission spectrum shows bright lines located at the exact same wavelengths as the dark lines in an absorption spectrum.

2. Spectroscopy is the study of the spectra emitted by astronomical objects like stars and planets. It is important because it allows the determination of the composition of the object being studied, as well as its temperature and density.

3. A spectroscope is composed of a slit that allows light to shine onto a prism or grating. Light is diffracted (bent) by the prism or grating through an angle that depends on the wavelength of the light. The spectrum is projected onto a screen or piece of film.

5. In the particle description of light, the color corresponds to the energy contained in each photon.

7. A hydrogen atom has a single proton in the nucleus and a single electron in one energy level (orbital).

9. Atoms are normally in the ground state, meaning that each electron is in the lowest possible energy level. This is the lowest energy state that the atom can be in. When one or more electrons are not in the lowest possible energy level, the energy of the atom is greater than that for the ground state, and the atom is said to be excited. An orbital is a sharply defined energy state that an electron can occupy in an atom.

10. Atoms emit and absorb radiation at characteristic frequencies that are determined by the energy levels the electrons can occupy. The energy levels in turn are determined by the structure of the nucleus of the atom. The difference between two electron energy levels is equal to the energy of the photon that must be emitted or absorbed by the atom when the electron makes that transition. With the photon's energy determined in this way, we can also calculate its frequency and wavelength.

13. Molecules can produce spectral lines unrelated to the movement of electrons between enery levels in two ways, via either rotational or vibrational transitions.

CHAPTER 5 Review & Discussion:

1. (i) Mirrors can be made larger than lenses because the full back of the mirror can be supported, whereas a lens can only be supported from its edges. (ii) Lenses suffer from chromatic aberration, whereas mirrors do not. (iii) Lenses absorb some of the light passing through them, while mirrors don't absorb any light because the light doesn't pass through the glass.

2. (i) Larger telescopes have more light gathering power, resulting in brighter images. (ii) Larger telescopes have better angular resolution, resulting in the ability to see smaller details in the source.

4. Due to the turbulence in the Earth's atmosphere, the best angular resolution that can be achieved from the ground is about 1 second of arc. The effects of atmospheric turbulence on the resolution limit are called ``seeing.''

5. The biggest advantage that the Hubble Space Telescope has over ground-based telescopes is that the ``seeing'' is ideal in space, due to the lack of atmospheric gases. The Hubble can therefore make observations down to the theoretical resolution limit of its design. A disadvantage of the Hubble is that it is not as large as some of the telescopes on Earth.

8. Radio telescopes have to be large because they detect radio waves, which can be hundreds of meters in wavelength.

10. Interferometry is the combination of data from several small telescopes to produce angular resolution equivalent to a single telescope with effective size equal to the distance between the two small telescopes. In radio astronomy, this yields angular resolution in the best cases of 0.001 seconds of arc, which is the best resolution achievable by any observing technique.

14. Studying objects at different wavelengths allows us to discover the temperatures of very hot and very cold objects, which don't emit primarily in the optical region of the electromagnetic spectrum. We can also learn about the properties of the distributions of particles, atoms, and molecules that make up the object.

CHAPTER 5 Problems:

3. A 6-m telescope has 3 times the radius of a 2-m telescope, and therefore it has 9 times the collecting area. Hence it requires only 1/9 hour (6 minutes and 40 seconds) to collect the same amount of light collected by a 2-m telescope in 1 hour. Similarly, a 12-m telescope has 6 times the radius of a 2-m telescope, and therefore it has 36 times the collecting area. Hence it requires only 1/36 hour (1 minute and 40 seconds) to collect the same amount of light collected by a 2-m telescope in 1 hour.

4. The formula for the angular resolution of a telescope is A=lambda / (40000 * D), where A is the angular resolution in arc seconds, D is the diameter of the telescope in meters, and lambda is the wavelength of the radiation in Angstroms. Note that according to this formula, A is proportional to lambda. Remember that in doing the calculations, you must express the wavelength in Angstroms!

In the problem, we are told that the angular resolution of the spaced-based telescope is 0.05 arc seconds for a wavelength of 700 nm. Since A is proportional to lambda, it follows that (i) A = 0.25 arc seconds for infrared radiation with a wavelength of 3.5 micrometers; (ii) A = 0.01 arc seconds for ultraviolet radiation with a wavelength of 140 nm.

CHAPTER 6 Review & Discussion:

4. The terrestrial planets are Mercury, Venus, Earth, and Mars. They are clustered in the inner solar system relatively close to the Sun, and are rocky in composition, with densities similar to that of Earth. The jovian planets are Jupiter, Saturn, Uranus, and Neptune. They are located in the outer solar system, and have densities much lower than Earth's. The jovian planets are composed mostly of gases. Pluto doesn't fit neatly into either category.

9. The terrestrial planets formed via "accretion" of the rocky material that was located in the inner region of the nebula from which the Sun and the planets formed 4.5 billion years ago. Accretion is a process in which larger and larger bodies form, and them join together to create even larger proto-planets. The process can also go in the other direction, when collisions between large proto-planets causes them to fragment. After millions of years, the number of terrestrial planets has stabilized to give us the set of planets that see in the solar system today.

CHAPTER 7 Review & Discussion:

1. The average density of Earth is higher than the density of the surface rocks and higher than the density of water. Hence the interior of the Earth must contain a high-density core.

2. A primary, pressure wave (P-wave) causes material to vibrate in a direction parallel to the motion of the wave. A secondary, shear wave (S-wave) causes material to vibrate in a direction perpendicular to the motion of the wave. P-waves can travel through both liquids and solids, but S-waves cannot travel through liquids.

4. By observing the distribution of P-waves and S-waves after an earthquake, scientists are able to deduce the existence of a liquid core inside the Earth.

8. Motions of the Earth's plates (continental drift) gives rise to surface features such as mountains and oceanic trenches.