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Comins DEU 3e Ch 08 Quiz 1 completed
The correct answers are written in bold, italic and underlined.
The most important questions to study for the exam are highlighted.
1. In what fundamental way do human beings (and many other animals)
utilize parallax for the measurement of distance?
• Our eyes focus back and forth continuously, and the brain interprets this focusing in terms of distance to the
object viewed.
• Our eyes are mounted horizontally about 10 cm apart in our heads, and the brain uses the relative look
angles of these eyes to estimate distance to the object viewed.
• We are always moving our heads slightly from side to side, and the brain compares look angles from each of
these positions to obtain the distance to the object viewed.
2. The distance to a nearby star is measured by observing
• the change in its apparent brightness over the course of a year because of the Earth's orbital motion.
• the apparent change in its position over one night because of the motion of the observer on a rotating Earth.
• the apparent change in its position with respect to more distant stars over a period of 1 year.
3. Why is stellar parallax considered the most accurate way to measure
the distance to a star?
• It relies solely on the brightness of a star and is independent of the measurement of angles or baselines.
• It gives the distance without having to measure either brightnesses or very small angles.
• It relies solely on the measurement of angles and baselines, and is independent of the brightness of a star.
4. The satellite that was put into orbit around the Earth specifically
to measure stellar parallaxes was
• Compton.
• Hipparcos.
• Hubble.
5. Using satellites, to what distance from the Earth have we been able
to measure stellar parallaxes with reasonable accuracy?
• About 100 pc
• About 150 pc
• About 500 pc
6. A star appears to move back and forth with a period of exactly 1 year
with respect to a distant galaxy that appears close to it in our sky.
What is the most likely cause of this observed motion?
• The observed motion is simply the motion of the star around the center of the galaxy.
•
•
The star has an unseen companion star, and the observed motion is due to the star's orbital motion around its
companion star with a period of exactly 1 year.
The star is relatively near the solar system, and the Earth's orbital motion produces an apparent change in
its position against the background (i.e., the galaxy) because of motion of the observer.
7. A star of magnitude +8 is
• brighter than a star of magnitude +5.
• fainter than a star of magnitude +5.
• impossible?the magnitude scale only runs from +1 to +6.
8. A star of magnitude -1 is
• brighter than a star of magnitude +1
• impossible because magnitudes cannot be negative!
• fainter than a star of magnitude +1
9. An astronomer makes a direct measurement of the brightness of a star
in the nighttime sky. What the astronomer has measured is
• the star's absolute magnitude.
• the star's apparent magnitude.
• the star's luminosity.
10. If we restrict our measurements to a specific band of color or
wavelength using an optical filter, what observations are necessary in
order to determine the absolute magnitude of a star at this color?
• Its apparent magnitude and its distance
• Its distance and its temperature
• Its apparent magnitude and its temperature
11. Two stars, P and Q, can be seen in the same region of our sky with
the same apparent magnitude, but star Q is 3 times as far away as star
P. What is the ratio of the intrinsic brightnesses of these stars, (star
P/star Q)?
• 1/9
• 1/3
• 9
12. How is the absolute magnitude of a star defined?
• It is the total energy emitted by the star per second, measured in joules/second or watts.
• It is the apparent magnitude a star would have if it were at an infinite distance.
• It is the apparent magnitude a star would have if it were at a standard distance of 10 pc.
13. According to the inverse-square law, if two stars have the same
absolute magnitude and if one star is 10 times farther away than the
other, then
• the more distant one would appear 100 times fainter.
•
•
the more distant one would appear 10 times fainter.
the more distant one would appear 100 magnitudes fainter.
14. The luminosity of a star is defined as
• the amount of energy received over unit area at the Earth's distance.
• the total amount of energy emitted from its surface every second.
• the amount of energy emitted from a unit area of its surface (e.g., 1 square meter) per second.
15. Astronomers have found that an important indicator of a star's
surface temperature is
• its brightness at different wavelengths.
• its absolute magnitude.
• its luminosity class.
16. The color of an isolated and very nearby star appears to be redder
than that of the Sun. Which of the following conclusions is the most
likely?
• The star is moving very rapidly away from the Sun.
• The star's temperature is lower than that of the Sun.
• Dust and gas between the star and the Earth has absorbed or scattered much of the blue light of the star.
17. A particular star has an apparent magnitude in a red filter of 5.60
and an apparent magnitude in a blue filter of 5.95. This information
tells us that the star is
• a cool star.
• an intrinsically very bright star.
• a hot star.
18. Three techniques that are used in astronomy to measure the
properties of astronomical objects are photometry, interferometry, and
spectroscopy. Which of these techniques allow us to measure a star's
temperature?
• Interferometry and spectroscopy
• Only spectroscopy
• Photometry and spectroscopy
19. Which of the following descriptions most closely describes the
changes that would be observed if a star were to increase its
temperature slowly over some period of time (e.g., a year)?
• The intensity of radiation from the star would rise, the peak of the overall continuum spectrum would shift to
shorter wavelengths, and the pattern of spectral absorption lines would change.
• The star's continuum spectrum would become bluer and more intense, but the pattern of absorption lines would
remain the same.
• The peak of the star's continuum spectrum would move toward the blue, but the overall intensity would not
change. Some absorption lines would become less strong while others would become stronger.
20. In the spectra of stars, absorption lines of hydrogen are produced
when atoms are excited from /n/ = 2 to higher levels. If hydrogen
absorption lines are very strong in the spectrum of a particular star,
what does this tell us about the temperature of the gas at this star's
surface?
• Intermediate temperature, about 10,000 K, exciting electrons from the ground state, /n/ = 1, to the first
excited state, /n/ = 2, but too small to excite them out of the atoms completely
• Very low temperature, 3000 K, because otherwise electrons in hydrogen atoms would have been excited to
much higher energy levels than /n/ = 2 and would not be available to absorb photons in the Balmer series at
visible wavelengths
• Very high surface temperature, about 40,000 K, so high energy photons and atomic collisions can excite the
electrons in essentially all hydrogen atoms out of the /n/ = 1 ground state