Stellar Astronomy Sample Questions for Exam 2

Chapter 4

1.         “Light” is

a)    always a wave and never anything else.

b)    always a particle and never anything else.

c)    a disturbance that travels through the luminiferous aether.

d)    electromagnetic radiation.

2.         The electromagnetic spectrum is

a)    part of a refracting telescope.

b)    the entire range of “light” from gamma rays to very long radio waves.

c)    visible light.

d)    “light” that is not visible to the human eye.

3.         The speed of light

a)    depends on the relative speed between the source and the observer.

b)    is different for different wavelengths.

c)    is dependent on the intensity of the light.

d)    is 299792458 ^m/_s for all observers regardless of their speed.

e)    None of the above, light is instantaneous.

4.         One of the basic principles of Einstein’s Special Relativity is

a)    The speed of light depends on the relative speed between the source and the observer.

b)    It is always possible determine who is moving and who is stationary.

c)    The observed laws of physics are the same regardless of any constant velocity at which you move.

d)    It is possible to move at speeds greater than the speed of light.

e)    All of the above.

5.         If an observer is stationary on the surface of the Earth and watches a spacecraft moving past at ⁹/₁₀ the speed of light he sees

a)    simultaneous flashes on the spacecraft appear simultaneous to both him and the person on the spacecraft

b)    the stationary observer sees the moving clock as running fast.

c)    the stationary observer sees the moving length as long.

d)    the stationary observer sees the moving clock as running slow.

e)    None of the above, everything is the same.

6.         The modern model of the atom is

a)   a solid mass with no internal structure.

b)   a small nucleus composed of neutrons and protons surrounded by a cloud of electrons.

c)    a small nucleus composed of electrons and protons surrounded by a cloud of neutrons.

d)   a small sphere composed of electrons, protons and neutrons.

7.         Atoms emit light when

a)   an electron spontaneously falls from a high energy state to a lower energy state.

b)   an electron spontaneously jumps from a low energy state to a high energy state.

c)    an electron completes one orbit around the nucleus.

d)   an electron is thrown out of the nucleus.

8.         An energy level diagram is

a)    a diagram of the energy production process in the sun.

b)    a diagram of the energy released when an atom is split.

c)    a diagram of the possible energies that an electron can have in an atom.

d)    a diagram showing the physical position of the electron as it orbits around the nucleus.

e)    None of the above.

9.         Blackbody radiation is

a)    the individual wavelengths of light emitted from black holes.

b)    the individual wavelengths of light that are absorbed by objects that are painted black.

c)    the continuous spectrum of light that is emitted from objects due to their temperature.

d)    the individual wavelengths of light that are emitted from objects due to their elemental composition.

e)    None of the above.

10.       Which of the following is not a property of blackbody radiation?

a)    The blackbody spectrum is a continuous spectrum of light.

b)    The wavelength of maximum intensity decreases with increasing temperature.

c)    The total energy emitted increases with increasing temperature.

d)    All wavelengths are emitted with equal intensity.

11.       The spectrum of the sun is

a)    a blackbody spectrum of the 5800° surface with emission lines from all the elements.

b)    a blackbody spectrum of the 5800° surface with absorption lines from all the elements.

c)    a hydrogen emission spectrum.

d)    an emission spectrum of hydrogen, helium and most of the other elements.

e)    None of the above, the sun doesn’t have a spectrum.

12.       The Doppler effect is

a)    the change in observed wavelength of a wave when the source is moving with respect to the observer.

b)    the change in the observed intensity of a wave when the source is moving with respect to the observer.

c)    the change in the observed speed of light when the source is moving with respect to the observer.

d)    the change in the observed position of a star due to the relative motion of the earth around the sun.

e)    None of the above.

13.       If a light source is moving towards you the light will be

a)    redshifted.

b)    blueshifted.

c)    unchanged.

d)    converted into mass.

e)    None of the above.

Short Answer Questions

1.            Describe a “blackbody” spectrum and how its shape and size depends on the temperature of the object producing it. Make a graph illustrating the blackbody spectra of several ideal blackbodies at different temperatures.

2.            Describe the modern model of the atom. Include descriptions of how the mass and charge are distributed, the composition of the nucleus, electron energy levels and the location of the electrons.

3.            Briefly discuss Einstein’s Special Theory of Relativity. What are the basic assumptions of the theory? What are some of the consequences of the theory on objects that are moving at speeds close to the speed of light?

4.            Describe the Doppler Effect and give at least two ways that it can affect the spectrum of a star.

Chapter 5

1.         Which of the following statements is false?

a)   Refraction is the bending of light when it passes from one medium to another.

b)   Mirrors experience chromatic aberration.

c)    Reflection is the “bouncing” of light off a surface.

d)   Spherical mirrors experience spherical aberration.

2.         The two basic types of optical telescopes are

a)   Galilean telescopes and Newtonian telescopes.

b)   reflecting telescopes and a refracting telescopes.

c)    Cassegrain telescopes and Copernican telescopes.

d)   long telescopes and short telescopes.

3.         The main function of a telescope is

a)   to magnify a stars image.

b)   to separate the light into its different colors.

c)    to clear up the distortions caused by the earth’s atmosphere.

d)   to gather a large amount of light and concentrate it at a focus.

4.         In a Newtonian telescope

a)    the eyepiece comes straight out the back of the telescope.

b)    two lenses are used to focus the light.

c)    the eyepiece comes out the side near the front of the telescope.

d)    dozens of hexagonal mirrors used to focus the light.

5.         The angular resolution of a telescope does not depend on

a)    the aperture size of the telescope.

b)    the wavelength of the light the telescope looks in.

c)    the brightness of the object being observed.

6.         Adaptive optics systems

a)    correct for the chromatic aberration caused by the use of lenses.

b)    improve the diffraction limit of a telescope.

c)    correct for atmospheric distortions.

d)    have been available for telescopes since the late 1800’s

7.         Today, the most precise astronomical observations are done using

a)    an eye placed to the eyepiece of a telescope.

b)    a CCD camera placed at the focal point of a telescope.

c)    a photographic plate placed at the focal point of a telescope.

d)    ordinary photographic film placed at the focal point of a telescope.

8.         A spectrograph is

a)    a device that combines the various colors together into white light.

b)    a device that separates the various intensities of light.

c)    a device that separates light into its’ constituent wavelengths.

d)    a device that filters out unwanted light from the background of a telescopic image.

9.         Radio telescopes are

a)    usually very small so that they can be pointed accurately.

b)    always located in outer space to since radio waves do not penetrate the atmosphere.

c)    can only “see” at night.

d)    are very large because the resolution of radio waves is so poor.

10.       Due to their poor resolution, the best radio observatories

a)    use huge radio dishes several miles across.

b)    use multiple radio dishes linked together in an interferometer.

c)    are orbiting spacecraft which are above Earth’s atmosphere.

11.       The LIGO observatory observes

a)    in microwave wavelengths.

b)    gravity waves.

c)    neutrinos.

d)    visible light from orbit

12.       Many types of astronomy can only be performed in space because

a)    objects in space are closer to the stars and can thus see more.

b)    gravity causes the telescopes to sag and in space the sag is eliminated because of weightlessness.

c)    the earth’s atmosphere blocks many of the wavelengths of the electromagnetic spectrum.

d)    clouds interfere with the observing and there are no clouds in space.

e)    All of the above.

13.       Which of the following statements is false ?

a)    The Hubble Telescope is a 2.4 m reflecting telescope in orbit that sees in wavelengths from near infrared to near ultraviolet.

b)    The Spitzer Space Telescope is a space based telescope that observes infrared wavelengths.

c)    The Chandra telescope is an orbiting X-ray telescope that was launched in the 1999.

d)    The FUSE telescope an orbiting telescope that observe in the gamma ray wavelengths.

Short Answer Questions

1.            Briefly describe the two main types of telescopes. Discuss the advantages and disadvantages of each type.

2.            Describe the criterion used in selecting observatory sites. Why is it that a few sites like Kitt Peak and Mauna Kea have so many telescopes? What are the qualities of these sites that make them so attractive to astronomers?

3.            Describe one of the major space-based telescopes and the wavelengths it observes in.

4.            Briefly describe a prism spectrometer. Include a diagram.

Chapter 13

1.         Stellar parallax

a)   can be accurately measured for stars less that 300 light-years away.

b)   does not exist because the earth does not move in the heavens.

c)    increases with the distance to the star.

d)   is too small to measure even with the largest telescopes and the closest stars.

2.         The parsec is defined as

a)    the distance at which a star shows a parallax of one arcsecond.

b)    the average distance between the earth and the sun.

c)    the distance to the nearest star.

d)    the distance light travels in one year.

3.         Stellar parallax is

a)    the real motion of stars through the universe.

b)    the distance unit used to measure the distance to planets.

c)    the change in the position of a star due to change in seasons.

d)    the apparent change in the direction of something due to a change in vantage point of the observer.

4.         To determine the luminosity of a star we need

a)   only the brightness of the star.

b)   only the distance to the star.

c)    both the brightness and the distance to the star.

d)   None of the above.

5.         The color ratio of a star is

a)    the ratio of the magnitude of the star observed through two different color filters.

b)    the ratio of the color of a star to its surface temperature.

c)    the ratio of the color of a star to its diameter.

d)    the ratio of the color of a star to the amount of interstellar reddening.

e)    None of the above.

6.         The stellar spectra classification scheme classifies according to

a)    the mass of the star.

b)    the surface temperature of the star.

c)    the diameter of the star.

d)    the distance to the star.

e)    None of the above.

7.         The absorption spectral lines of hydrogen are weaker for stars at the lowest surface temperatures because

a)   cooler stars have less hydrogen.

b)   the hydrogen has sunk to a hotter level.

c)    at low temperatures the hydrogen emits light instead of absorbing light so there is no absorption spectrum.

d)   at low temperatures all the hydrogen is in the ground state so no electrons are in the excited states that are responsible for absorption.

e)   None of the above, the coolest stars have the strongest hydrogen absorption spectra.

8.         By spectral class, the hottest to coolest stars are

a)    M, K, G, F, A, B & O

b)    A, B, C, D, E, F & G

c)    A, B, F, G, K, M & O

d)    O, B, A, F, G, K & M

9.         The Hertzsprung-Russell diagram is

a)   a plot of mass versus luminosity of stars.

b)   a plot of luminosity versus temperature of stars.

c)    a plot of luminosity versus distance of stars.

d)   a plot of mass versus temperature of stars.

10.       On an H-R diagram, most stars lie in the region called the

a)    main sequence.

b)    subgiant sequence.

c)    giant sequence.

d)    supergiant sequence.

e)    None of the above.

11.       On an H-R diagram, the stars in the top right corner are

a)    supergiants.

b)    white dwarfs.

c)    main sequence.

d)    red dwarfs.

12.       A binary star system is

a)   a single star with a large planet orbiting it.

b)   two stars of equal mass passing each other in space.

c)    two stars in orbit around a common center of mass.

d)   a star that switches on and off in binary code.

e)   None of the above.

13.       Observing binary star systems is important because

a)    they allow us to accurately determine the distance to stars.

b)    they allow us to accurately measure the luminosity of stars.

c)    they allow us to accurately measure the color index of stars.

d)    they allow us to accurately determine the mass of stars.

e)    None of the above, there is no special reason to observe binary star systems.

14.       An eclipsing binary is one in which

a)    both stars are easily visible to the naked eye.

b)    the individual stars can only be identified by their spectra.

c)    both stars can be resolved in a telescope.

d)    the stars pass directly in front of each other, eclipsing each other.

e)    None of the above.

15.       By studying eclipsing binaries we can determine

a)    the individual spectra of both stars.

b)    the diameters of both of the stars.

c)    the masses of both of the stars.

d)    All of the above.

Short Answer Questions

1.    Sketch an H-R diagram. Assume you are plotting a sample of 100 stars that are a good representation of all stars. Label the location of supergiants, main sequence and white dwarf stars.

2.    Explain why the distance to some stars can be determined by parallax but most stellar distances cannot.

3.    Describe the different properties of main sequence stars that are determined by the mass of the star. Why is mass so important to the characteristics of a star?

4.    Why is it so important to study binary systems? What information can be gained from them that can’t be otherwise?