exam 1

Question 1

An eclipse of the Moon can be observed only during a ________, while an eclipse of the Sun can be observed only during a ________
a) new moon; new moon
b) full moon; new moon
c) full moon; full moon
d) third quarter moon; new moon
e) new moon; full moon

Answer 1

b) full moon; new moon *

Question 2

As we view stars around the North Celestial Pole from Fairfax, they appear to rotate ________ around Polaris while stars in the eastern sky appear to ________.
a) clockwise; set
b) clockwise; rise
c) counter-clockwise; set
d) counter-clockwise; rise

Answer 2

d) counter-clockwise; rise *

Question 3

It is colder in winter than in summer because
a) There is more snow in winter.
b) The Earth is farther from the Sun during winter.
c) The Moon is farther from the Earth in winter.
d) The tilt of the Earth’s axis causes the Sun to be lower in the sky during winter.

Answer 3

d) The tilt of the Earth’s axis causes the Sun to be lower in the sky during winter. *

Question 4

If a light source is receding from you at high speed, then the Doppler effect causes
a) the frequency of the light to be increased.
b) the frequency of the light to be reduced.
c) the energy of the light to be increased.
d) the wavelength of the light to be reduced.
e) interference.

Answer 4

b) the frequency of the light to be reduced. *

Question 5

In the Copernican model of the solar system, retrograde motion of Mars occurs
a) only during a lunar eclipse.
b) every solar day.
c) every 24 sidereal hours.
d) when the line between the Earth and the Sun passes over the line between Mars and the Sun.
e) only during a solar eclipse

Answer 5

d) when the line between the Earth and the Sun passes over the line between Mars and the Sun. *

Question 6

Galileo’s observations of the full phase of Venus were inconsistent with the Ptolemaic model of the solar system because
a) In the Ptolemaic model the Sun is at the center of the solar system.
b) In the Ptolemaic model the the Earth is flat.
c) The shadow of the Earth on the Moon during a lunar eclipse is always a circle.
d) In the Ptolemaic model Venus is always closer to the Earth than the Sun is.
e) In the Ptolemaic model Venus is always farther from the Earth than the Sun is.

Answer 6

d) In the Ptolemaic model Venus is always closer to the Earth than the Sun is. *

Question 7

Aristarchus hypothesized that the Earth revolves around the Sun. Which of the following is a reason that the other Greek philosophers used to reject his idea?
a) The stellar parallax could not be observed.
b) The angular size of stars could not be measured.
c) The Earth was thought to be flat.
d) The Sun blocked measurement of parallax.
e) Parallax did not yet exist for stars.

Answer 7

a) The stellar parallax could not be observed. *

Question 8

Suppose you point a telescope at a star and then clamp the telescope to the ground so that it can’t move. If you wait ________, then the telescope will be pointing to a different star with ________.
a) one solar hour; the same declination but one more hour of right ascension
b) one sidereal hour; the same declination but one more hour of right ascension
c) one sidereal hour; the same right ascension but one more degree of declination
d) one solar hour; the same right ascension but one more degree of declination

Answer 8

b) one sidereal hour; the same declination but one more hour of right ascension *

Question 9

On March 21, the Sun is located
a) 45 degrees above the horizon for Fairfax.
b) on or near the celestial equator.
c) 23 1/2 degrees North of the celestial equator.
d) near the North celestial pole.

Answer 9

b) on or near the celestial equator. *

Question 10

If the distance between two objects is increased by a factor of 4, then the gravitational force between them will
a) increase by a factor of 4.
b) decrease by a factor of 16.
c) increase by a factor of 2.
d) decrease by a factor of 32.
e) it can’t be determined from the available information

Answer 10

b) decrease by a factor of 16. *

Question 11

When a lunar eclipse occurs, it can be seen from
a) the south pole only.
b) the north pole only.
c) the equator only.
d) anyplace on the day side of the Earth.
e) anyplace on the night side of the Earth.

Answer 11

e) anyplace on the night side of the Earth. *

Question 12

The stars return to the same positions in the sky every
a) solar day.
b) 24 sidereal hours.
c) synodic month.
d) 24 solar hours.
e) all of the above.

Answer 12

b) 24 sidereal hours. *

Question 13

Consider the equation F = m a, where F is the applied force, m is the mass of the object, and a is the resulting acceleration. If we ________ while holding m constant, we ________.
a) double F; double a
b) halve F; halve a
c) double F; halve a
d) halve F; double a
e) both a) and b)

Answer 13

a) double F; double a
b) halve F; halve a

e) both a) and b) *

Question 14

The semimajor axis of an ellipse is
a) the width of the ellipse measured across the longest dimension.
b) equal to the period of the orbit.
c) half the width of the ellipse measured across the shortest dimension.
d) half the width of the ellipse measured across the longest dimension.

Answer 14

d) half the width of the ellipse measured across the longest dimension. *

Question 15

The equation relating the distance D to the parallax angle alpha is given by

D = (180 * R) / (pi * alpha)

where the parallax angle alpha is assumed to be in degrees and R = 6,378 km is the Earth’s radius. If the parallax angle is 2 arc-seconds (2”), then the distance D to the object in space is

a) 6.6 x 10 ** 7 km
b) 6.6 x 10 ** 8 km
c) 6.6 x 10 ** 9 km
d) 3.3 x 10 ** 7 km
e) 3.3 x 10 ** 8 km

Answer 15

b) 6.6 x 10 ** 8 km *

Question 16

Kepler’s second law implies that
a) Mars travels more quickly than the Earth.
b) Venus travels more slowly than the Earth.
c) planets travel with higher speed as they get closer to the Sun.
d) planets travel with lower speed as they get closer to the Sun.

Answer 16

c) planets travel with higher speed as they get closer to the Sun. *

Question 17

Red light has a
a) shorter wavelength and a higher energy than blue light.
b) longer wavelength and a lower energy than blue light.
c) shorter wavelength and a lower energy than blue light.
d) longer wavelength and a higher energy than blue light.

Answer 17

b) longer wavelength and a lower energy than blue light. *

Question 18

According to Stefan’s Law, the energy radiated by an object per unit time varies in proportion to T ** 4, where T is the temperature of the object. This means that if we double the temperature, the radiated energy changes by a factor of ________.
a) 2
b) 3
c) 4
d) 16
e) 256

Answer 18

d) 16 *

Question 19

According to Kepler’s third law, P ** 2 = a ** 3, where P is the orbital period measured in Earth years and a is the length of the semi-major axis measured in astronomical units. For the planet Jupiter, a = 5.2, and therefore its orbital period is
a) 1.9 Earth years.
b) 141 Earth years.
c) 11.9 Earth years.
d) 27 Earth years.
e) 2 Earth years.

Answer 19

c) 11.9 Earth years. *

Question 20

An annular eclipse occurs when the Sun, Moon, and Earth line up, and
a) the Earth is at its minimum distance from the Sun.
b) the Earth is at its maximum distance from the Sun.
c) the Moon is at its minimum distance from the Earth.
d) the Moon is at its maximum distance from the Earth.

Answer 20

d) the Moon is at its maximum distance from the Earth. *

Question 21

How high is the North Celestial Pole (i.e., the star Polaris) above the horizon for an observer at a latitude of 25 degrees North?
a) 38 degrees.
b) 12 degrees.
c) 45 degrees.
d) 25 degrees.
e) it can’t be determined from the available information.

Answer 21

d) 25 degrees. *

Question 22

Which astronomer from the Copernican revolution made the first systematic telescopic observations of the sky? Which astronomer from the Copernican revolution carefully analyzed and plotted Tycho Brahe’s data and deduced the 3 laws of planetary motion?

a) Newton; Galileo
b) Galileo; Kepler
c) Kepler; Newton
d) Galileo; Brahe
e) Copernicus; Kepler

Answer 22

b) Galileo; Kepler *

Question 23

A total eclipse of the Sun is observed from inside the ________. A partial solar eclipse is observed from inside the ________.

a) umbra; penumbra
b) penumbra; umbra
c) north pole; south pole
d) south pole; north pole
e) celestial equator

Answer 23

a) umbra; penumbra *

Question 24

Retrograde motion occurs when a planet appears to move

a) westward relative to the stars.
b) eastward relative to the stars.
c) toward the Sun.
d) toward the Moon.

Answer 24

a) westward relative to the stars. *

Question 25

One sidereal day is ________ than one solar day

a) 4.8 hours shorter
b) 4.8 hours longer
c) 3.9 minutes shorter
d) 3.9 minutes longer
e) 3.9 seconds shorter

Answer 25

c) 3.9 minutes shorter *

Question 26

According to Wien’s law, the peak of the Planck curve for a 1000K object is

a) bluer than for a 5000K object.
b) redder than for a 5000K object.
c) bluer than for a 7000K object.
d) cannot be detected by any instrument.
e) none of the above.

Answer 26

b) redder than for a 5000K object. *

Question 27

The angle subtended by an American dime at a distance of 3 miles is one arc second. From a distance of 9 miles, an American dime therefore subtends an angle of

a) 30 arc seconds
b) 2 arc seconds
c) 1/3 arc second
d) 1 arc minute
e) 1 degree

Answer 27

c) 1/3 arc second *

Question 28

The south celestial pole is located at celestial coordinates

a) 0 hours RA, 0 degrees DEC
b) 24 hours RA, 0 degrees DEC
c) 24 hours RA, 90 degrees DEC
d) 0 hours RA, 90 degrees DEC
e) 0 hours RA, -90 degrees DEC

Answer 28

e) 0 hours RA, -90 degrees DEC *

Question 29

Although the Moon and the Sun have about the same angular size as viewed from the Earth, eclipses are relatively rare because

a) people are usually asleep during them.
b) the Moon always shows the same face to the Earth.
c) new moons don’t normally occur during full moons.
d) the Moon’s orbit is tilted with respect to the Earth’s orbit.
e) the Sun and the Moon have to come into direct contact.

Answer 29

d) the Moon’s orbit is tilted with respect to the Earth’s orbit. *

Question 30

Which astronomer from the Copernican revolution made the best naked-eye observations of the planetary positions? Which astronomer from the Copernican revolution developed the physical laws explaining why the planets follow elliptical orbits?

a) Brahe; Copernicus
b) Galileo; Brahe
c) Galileo; Kepler
d) Brahe; Newton
e) Newton; Brahe

Answer 30

d) Brahe; Newton *

Question 31

Consider the accompanying triangle with a base of 25 meters. Using trigonometry, the result obtained for the height h is

a) h = 25 meters * sin(75 degrees) = 33.0 meters
b) h = 25 meters * tan(15 degrees) = 48.7 meters
c) h = 25 meters * tan(75 degrees) = 93.3 meters
d) h = 25 meters * tan(75 degrees) = 26.0 meters
e) h = 25 meters * cos(15 degrees) = 75.0 meters

Answer 31

c) h = 25 meters * tan(75 degrees) = 93.3 meters *

Question 32

What is a constellation? Why are the constellations useful for mapping the sky?

Answer 32

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.

Question 33

Describe the daily and annual motions of the sun, Moon, and stars as viewed from the earth

Answer 33

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.

Question 34

How and why does a day measured with respect to the sun differ from a day measured with respect to the stars?

Answer 34

The day measured by the stars (the sidereal 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.

Question 35

Why do we see different stars at different times of the year?

Answer 35

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

Question 36

Why are there seasons on earth?

Answer 36

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.

Question 37

How much of the moon’s surface is lit by the sun at any one time? why do we see different phases of the moon?

Answer 37

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.

Question 38

What causes a lunar eclipse? A solar eclipse? why aren’t there lunar and solar eclipses every month?

Answer 38

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.

Question 39

How far does light travel is one second? if this light were leaving Houston, what location (on earth or beyond) would it reach in one second?

Answer 39

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).

Question 40

Write the following numbers in scientific
notation : 1000;
0.000001;
1001;
1,000,000,000,000,000;
123,000;
0.000456.

Answer 40

(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)

Question 41

Write the following numbers in “normal” numerical form:
3.16 X 10 ** 7;
2.998 x 10 ** 3;
6.67 x 10 ** -11;
2 x 10 ** 0

Answer 41

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

Question 42

Calculate:
(2 x 10 ** 3) + 10 ** -2
(1.99 x 10 ** 30)/ (5.98 x 10 ** 24)
(3.16 x 10 ** 7) x (2.998 x 10 ** 5)

Answer 42

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

Question 43

Relative to the stars, through how many degrees, arc minutes, or arc seconds does the Moon move in
(a) 1 hour of time;
(b) 1 minute;
(c) 1 second?
How long does it take for the Moon to move a distance equal to its own diameter?

Answer 43

The Moon moves through 360 degrees per month, as viewed from the Earth. There are 30 x 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.

Question 44

Briefly describe the geocentric model of the universe and explain why it was accepted for so long.

Answer 44

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.

Question 45

The benefit of our current knowledge lets us see flaws in the Ptolemaic model of the universe. What is its
basic flaw?

Answer 45

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

Question 46

What was the great contribution of Copernicus to our knowledge of the solar system? How was his model “still flawed?

Answer 46

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.

Question 47

What discoveries of Galileo helped confirm the views of Copernicus, and how did they do so?

Answer 47

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.

Question 48

Briefly describe Kepler’s three laws of planetary motion.

Answer 48

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.

Question 49

What does it mean to say that Kepler’s laws are empirical?

Answer 49

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.

Question 50

What is the relationship between wavelength, wave frequency, and of a wave velocity?

Answer 50

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.

Question 51

What’s so special about c?

Answer 51

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

Question 52

What do radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays have in common? How do they differ?

Answer 52

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.

Question 53

What is a blackbody? What are the main characteristics of the radiation it emits?

Answer 53

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.

Question 54

What does Wien’s law reveal about stars in the sky?

Answer 54

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

Question 55

How do astronomers use the Doppler effect to determine the velocities of astronomical objects? What are some possible limitations of this approach?

Answer 55

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.

Question 56

A sound wave moving through water has a frequency of 256 Hz and a wavelength of 5.77 m. What is the speed of the wave?

Answer 56

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.

Question 57

Two otherwise identical objects have temperatures of 300 Kand 1500 K, respectively. Which one radiates more energy, and by what factor does its emission exceed the
emission of the other?

Answer 57

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.