Astronomy Exam 2 Part 4

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  • 1/10 Questions

    Based on the rotation curves of stars in spiral galaxies and the Milky Way, most of the mass in galaxies is believed to be in the form of

    • A. dark matter.
    • B. neutral hydrogen.
    • C. luminous stars.
    • D. ionized hydrogen.
    • E. black holes.
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About This Quiz

Astronomy Exam 2 part 4 assesses knowledge on cosmic phenomena, including the use of Cepheid variable stars for measuring distances, galaxy rotation through Doppler shifts, and universe structure based on density. Essential for students in astrophysics and cosmology.

Astronomy Exam 2 Part 4 - Quiz

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  • 2. 

    What is meant by dark matter?

    • A. Mass that disappears into black holes.

    • B. Mass made of anti-matter whose effect cancels out the gravity of ordinary matter.

    • C. Mass that radiates strongly at X-ray wavelengths and is therefore invisible with ordinary light.

    • D. Mass deduced to be present from its gravitational effect but which emits no visible light or other detectable radiation

    • E. None of the above.

    Correct Answer
    A. D. Mass deduced to be present from its gravitational effect but which emits no visible light or other detectable radiation
    Explanation
    Dark matter refers to mass that is inferred to exist based on its gravitational effects, but does not emit any visible light or other detectable radiation. This means that dark matter cannot be directly observed or detected using ordinary methods of observation. It is believed to make up a significant portion of the total mass in the universe, and its presence is necessary to explain various astronomical observations and the structure of galaxies. Options A, B, and C do not accurately describe dark matter, making option D the correct answer.

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  • 3. 

     

    • A. the universe is expanding.

    • B. the fabric of space is curved by the presence of mass.

    • C. all galaxies see themselves at the center of universal expansion.

    • D. light travels at a finite velocity and takes time to get to us.

    • E. the universe had a distinct beginning about 15 billion years ago.

    Correct Answer
    A. D. light travels at a finite velocity and takes time to get to us.
    Explanation
    Light travels at a finite velocity and takes time to reach us. This means that the light we receive from distant objects has traveled for a certain amount of time before reaching our eyes. Since the speed of light is not infinite, the light from these objects takes a significant amount of time to reach us. Therefore, when we observe distant objects, we are actually seeing them as they appeared in the past, because the light we see has taken time to travel to us.

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  • 4. 

    Whether the universe is open, closed or flat depends on the

    • A. luminosity

    • B. temperature

    • C. radius

    • D. rotation rate

    • E. density

    Correct Answer
    A. E. density
    Explanation
    The correct answer is E. density. The open, closed, or flat nature of the universe depends on its overall density. If the density is high enough, the universe is closed and will eventually collapse in on itself. If the density is too low, the universe is open and will continue to expand forever. If the density is just right, the universe is flat and will also continue to expand forever, but at a decreasing rate. Luminosity, temperature, radius, and rotation rate do not determine the overall nature of the universe.

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  • 5. 

    Astronomers use Cepheid variable stars to measure galaxies’ distances because

    • A. the faster they vary, the more distant they are.

    • B. their luminosity can be determined from their period of variation.

    • C. they obey Hubble’s law.

    • D. they are the most common type of main-sequence star visible in galaxies.

    • E. they all lie in the same spot on the HR diagram.

    Correct Answer
    A. B. their luminosity can be determined from their period of variation.
    Explanation
    Cepheid variable stars are used by astronomers to measure galaxies' distances because their luminosity can be determined from their period of variation. Cepheids are pulsating stars that vary in brightness over a regular period of time. The period of variation is directly related to the star's intrinsic luminosity, allowing astronomers to calculate their distance based on the observed brightness. This relationship between period and luminosity has been well-established and is used as a standard candle for distance measurements in astronomy.

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  • 6. 

     Hubble’s law

    • A. tells us that the universe is expanding.

    • B. permits us to measure the distances to distant galaxies and quasars.

    • C. implies that the universe had a beginning about 15 billion years ago.

    • D. says that more distant galaxies recede more rapidly than nearby ones.

    • E. all of the above.

    Correct Answer
    A. E. all of the above.
    Explanation
    Hubble's law states that the universe is expanding, which is option A. It also allows us to measure the distances to distant galaxies and quasars, which is option B. Additionally, Hubble's law implies that the universe had a beginning about 15 billion years ago, which is option C. Lastly, the law states that more distant galaxies recede more rapidly than nearby ones, which is option D. Therefore, the correct answer is E, all of the above, as all the statements are supported by Hubble's law.

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  • 7. 

     Most of the helium in the Universe is believed to be produced in

    • A. red giants.

    • B. main-sequence stars.

    • C. planetary nebulae.

    • D. the Big Bang.

    • E. supernovae.

    Correct Answer
    A. D. the Big Bang.
    Explanation
    The correct answer is D. the Big Bang. During the Big Bang, the Universe underwent a rapid expansion and cooling. This allowed for the formation of light elements such as helium, which is believed to have been produced in abundance during this early stage of the Universe. As the Universe continued to evolve, helium was then incorporated into the formation of stars and other celestial bodies. Therefore, the majority of helium in the Universe is thought to have originated from the Big Bang.

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  • 8. 

    Edwin Hubble recognized that the Andromeda nebula was a separate ”island universe” rather than a component of our own galaxy because

    • A. he observed that the nebula was rotating.

    • B. he used Cepheid variables to find it was a tremendous distance away.

    • C. he determined that the nebula was moving away from our Galaxy.

    • D. he counted that there were more than one billion stars in the nebula.

    • E. he detected dust and gas in the nebula.

    Correct Answer
    A. B. he used Cepheid variables to find it was a tremendous distance away.
    Explanation
    Edwin Hubble recognized that the Andromeda nebula was a separate "island universe" rather than a component of our own galaxy because he used Cepheid variables to find it was a tremendous distance away. Cepheid variables are stars that pulsate in a regular pattern, and their brightness is directly related to their period of pulsation. By observing the brightness of Cepheid variables in the Andromeda nebula, Hubble was able to determine their true brightness and calculate their distance. He found that the Andromeda nebula was much farther away than any known stars in our galaxy, indicating that it was a separate entity.

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  • 9. 

    Spiral galaxies are known to rotate by measuring

    • A. the Doppler shifts of stars on each side of its center.

    • B. the relative motions of other galaxies inside them.

    • C. the length and curvature of their spiral arms.

    • D. the time it takes individual stars to orbit the center.

    • E. None of the above—galaxies don’t rotate.

    Correct Answer
    A. A. the Doppler shifts of stars on each side of its center.
    Explanation
    Spiral galaxies are known to rotate by measuring the Doppler shifts of stars on each side of its center. The Doppler shift occurs when an object is moving towards or away from an observer, causing a shift in the wavelength of the light it emits. By measuring the Doppler shifts of stars on each side of its center, astronomers can determine the rotational motion of the galaxy. This method allows them to understand the dynamics and structure of spiral galaxies.

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  • 10. 

    An astronomer now living in another galaxy far away from ours would see

    • A. some of the most distant galaxies coming toward her and some going away from her.

    • B. many more nearby quasars than we do.

    • C. our Galaxy approaching her.

    • D. the more-or-less same relation between redshift and distance that we see.

    • E. All of the above.

    Correct Answer
    A. D. the more-or-less same relation between redshift and distance that we see.
    Explanation
    An astronomer living in another galaxy would see the same relation between redshift and distance that we observe. This is because the redshift of light from distant objects is caused by the expansion of the universe, which affects all galaxies regardless of their location. As objects get farther away, their light is stretched to longer wavelengths, resulting in a redshift. This redshift is directly related to the distance of the object, meaning that the farther the object, the greater the redshift. Therefore, an astronomer in another galaxy would observe a similar relationship between redshift and distance as we do.

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  • Current Version
  • Jun 09, 2024
    Quiz Edited by
    ProProfs Editorial Team
  • Apr 29, 2010
    Quiz Created by
    Mllanos87
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