AST104 Mastering Astronomy: Spectra
Exam Questions and Answers
Which of the following conditions lead you to see an absorption line spectrum
from a cloud of gas in interstellar space?
•The cloud is visible primarily because it reflects light from nearby stars.
•The cloud is extremely hot.
•The cloud is cool and lies between you and a hot star.
•The cloud is cool and very dense, so that you cannot see any objects that lie
behind it. - ✅✅The cloud is cool and lies between you and a hot star.
Suppose you see two stars: a blue star and a red star. Which of the following can
you conclude about the two stars? Assume that no Doppler shifts are involved.
(Hint: Think about the laws of thermal radiation.)
•The blue star is farther away than the red star.
•The red star is more massive than the blue star.
•The blue star has a hotter surface temperature than the red star.
•The red star has a hotter surface temperature than the blue star.
•The blue star is more massive than the red star. - ✅✅The blue star has a
hotter surface temperature than the red star.
Suppose you want to know the chemical composition of a distant star. Which
piece of information is most useful to you?
, •the Doppler shift of the star's spectrum
•the peak energy of the star's thermal radiation
•the wavelengths of spectral lines in the star's spectrum
•whether the star's spectrum has more emission lines or more absorption lines -
✅✅the wavelengths of spectral lines in the star's spectrum
The set of spectral lines that we see in a star's spectrum depends on the star's:
•interior temperature.
•chemical composition.
•rotation rate. - ✅✅chemical composition
The higher the energy of a photon, the ________ its wavelength.
•shorter
•longer
•stronger - ✅✅shorter
Study the graph of the intensity of light versus wavelength for continuous spectra,
observing how it changes with the temperature of the light bulb. Recall that one
of the laws of thermal radiation states that a higher-temperature object emits
photons with higher average energy (Wien's law). This law is illustrated by the
fact that for a higher temperature object, the graph peaks at __________.
•a longer wavelength
•a higher intensity
Exam Questions and Answers
Which of the following conditions lead you to see an absorption line spectrum
from a cloud of gas in interstellar space?
•The cloud is visible primarily because it reflects light from nearby stars.
•The cloud is extremely hot.
•The cloud is cool and lies between you and a hot star.
•The cloud is cool and very dense, so that you cannot see any objects that lie
behind it. - ✅✅The cloud is cool and lies between you and a hot star.
Suppose you see two stars: a blue star and a red star. Which of the following can
you conclude about the two stars? Assume that no Doppler shifts are involved.
(Hint: Think about the laws of thermal radiation.)
•The blue star is farther away than the red star.
•The red star is more massive than the blue star.
•The blue star has a hotter surface temperature than the red star.
•The red star has a hotter surface temperature than the blue star.
•The blue star is more massive than the red star. - ✅✅The blue star has a
hotter surface temperature than the red star.
Suppose you want to know the chemical composition of a distant star. Which
piece of information is most useful to you?
, •the Doppler shift of the star's spectrum
•the peak energy of the star's thermal radiation
•the wavelengths of spectral lines in the star's spectrum
•whether the star's spectrum has more emission lines or more absorption lines -
✅✅the wavelengths of spectral lines in the star's spectrum
The set of spectral lines that we see in a star's spectrum depends on the star's:
•interior temperature.
•chemical composition.
•rotation rate. - ✅✅chemical composition
The higher the energy of a photon, the ________ its wavelength.
•shorter
•longer
•stronger - ✅✅shorter
Study the graph of the intensity of light versus wavelength for continuous spectra,
observing how it changes with the temperature of the light bulb. Recall that one
of the laws of thermal radiation states that a higher-temperature object emits
photons with higher average energy (Wien's law). This law is illustrated by the
fact that for a higher temperature object, the graph peaks at __________.
•a longer wavelength
•a higher intensity
