CHAPTER 1 Review & Discussion:

4. A constellation is a chance grouping of stars as viewed from the Earth. Usually the stars in a constellation are not actually close to each other, but simply appear to be near each other in the sky.

5. The Sun, Moon, and stars all rise in the east and set in the west (diurnal motion) due to the daily rotation of the Earth.

6. The day measured by the stars (the sideal day) is about 4 minutes shorter than the day measured by the Sun (the solar day) because it takes 4 minutes for the Earth to rotate the extra amount required for the Sun to return to the same place in the sky. The extra 4 minutes is due to the fact that each day the Earth moves along in its orbit around the Sun.

7. We see different stars in summer and winter because the Sun is in different parts of the sky during the year.

9. Seasons occur on Earth due to the tilt of the Earth's axis of rotation. This changes the angle of the Sun in the sky, which alters the heating of the surface.

10. We see phases of the Moon because of the changing angle between the Earth, Sun, and Moon. Although one complete hemisphere of the Moon is always lit by the Sun, this is not always the hemisphere visible from Earth.

11. A lunar eclipse occurs when the Earth passes between the Sun and the Moon. A solar eclipse occurs when the Moon passes between the Sun and the Earth. This can only happen when the line of nodes points towards the Sun (eclipse season). The line of nodes is the intersection of the Moon and Earth orbital planes. Eclipses do not occur every month because the proper alignment can only be achieved during an eclipse season. There are two eclipse seasons per year, which occur when the Earth and the Sun lie on the line of nodes.

CHAPTER 1 Problems:

1. The speed of light is 3 x 10**10 centimeters per second. In one second, light travels 3 x 10**10 centimeters, or 3 x 10**8 meters, or 3 x 10**5 kilometers. This is about the distance from Los Angeles to the Moon, so the correct answer is (c).

2. (a) Write numbers in scientific notation:

1000 = 10**3

0.000001 = 10**(-6)

1001 = 1.001 x 10**3

1,000,000,000,000,000 = 10**15

123,000 = 1.23 x 10**5

0.000456 = 4.56 x 10**(-4)

(b) Write numbers in "normal" notation:

3.16 x 10**7 = 31,600,000

2.998 x 10**5 = 299,800

6.67 x 10**(-11) = 0.0000000000667

2 x 10**0 = 2

(c) Calculate results:

(2 x 10**3) + 10**(-2) = 2000.01

(1.99 x 10**30) / (5.97 x 10**24) = 3.3333 x 10**5

(3.16 x 10**7) x (2.998 x 10**5) = 9.47368 x 10**12

4. The Moon moves through 360 degrees per month, as viewed from the Earth. There are 30*24=720 hours per month, so

(a) in one hour the Moon moves 0.5 degrees = 30 arc minutes = 1,800 arc seconds.

(b) in one minute the Moon moves 8.3 x 10**(-3) degrees = 0.5 arc minutes = 30 arc seconds

(c) in one second the Moon moves 1.4 x 10**(-4) degrees = 8.3 x 10**(-3) arc minutes = 0.5 arc seconds

Since the angular diameter of the Moon is about 0.5 degree, it takes about one hour for the Moon to move an angular distance equal to its own diameter.

CHAPTER 2 Review & Discussion:

2. In the geocentric model of the universe, the Earth is at the center, and the planets, the Sun, and the Moon all travel around the Earth. The planets travel on epicycles connected to circular deferents in order to explain the observed retrograde motion.

3. The basic flaw of the Ptolemaic model is that it is geocentric.

4. In the Copernican model, the Sun is at the center. A remaining flaw, however, is the continued presence of epicycles, which are necessary because only circular motions were allowed in the model.

6. With the newly-invented telescope, Galileo discovered the phases Venus; the satellites of Jupiter; spots on the Sun; and irregularities on the Moon. All of these observations supported the Copernican model.

8. Kepler's First Law: The orbital paths of the planets are elliptical (not circular), with the Sun at one focus.

Kepler's Second Law: An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time.

Kepler's Third Law: The square of a planet's orbital period is proportional to the cube of its semi-major axis.

10. Kepler's laws are empirical in nature, which means that they resulted solely from the analysis of observational data and were not derived from a theory or mathematical model. Kepler apparently had no appreciation for the physics underlying his laws.

CHAPTER 3 Review & Discussion:

2. The period of a wave is the amount of time between peaks.

The wavelength of a wave is the distance between peaks.

The amplitude of a wave is the maximum height.

The frequency of a wave is the number of peaks that pass by per second.

The wave velocity is equal to the wavelength multiplied by the frequency.

6. c is the speed of light, which is the same for all observers.

11. All of these waves are parts of the electromagnetic spectrum, which means they are propagated by oscillating electric and magnetic fields. However, they have different wavelengths, frequencies, and energies.

12. A black body is an object that absorbs and reemits all radiation falling upon it, so that it is in equilibrium with its surroundings. The radiation emitted by a black body is characteristic of its temperature. The spectrum of the radiation emitted by a black body is called the Planck spectrum.

14. Wien's law tells us the temperature of stars based upon their color. Blue stars are hotter than red stars.

15. The Doppler effect is an apparent change in the wavelength of radiation due to the relative velocity between the source and the observer. The wavelength of the radiation appears to be larger for an observer moving away from the source, and smaller for an observer moving towards the source.

CHAPTER 3 Problems:

1. The wave velocity is equal to the wavelength multiplied by the frequency. Therefore the speed of sound in water is 256 Hz * 5.77 m = 1,477.12 m/sec.

6. Let object A have a temperature of 300K and object B have a temperature of 1500 K, respectively. Both objects have the same size. Therefore, according to Stefan's Law, the body with the higher temperature radiates (1500/300)^4 times more energy per unit time than does the cooler body. This works out to a factor of 625 times more energy.