in order for an interstellar cloud to collapse gravitationally, it must
A not have any spin.
B have a very large mass.
C be made mostly of hydrogen.
D have a low internal pressure compared to its gravity.
E have a high internal pressure compared to its gravity.
21-cm radiation has yielded important information about
A the density of helium in the universe
B the physical structure of our galaxy
C the prevalence of water in the universe
D the spin-flip propensities of methyl alcohol (ch2oh)
dark clouds are best studied through examination of
A interstellar absorption lines in the spectra of distant stars
B Balmer emission lines
C radio waves emitted by molecules
D ultraviolet radiation emitted by the gas
interstellar molecules are most abundant in
A dark clouds
B emission nebulae
C reflection nebulae
D between spiral arms
interstellar 21-cm radiation is emitted by
A water
B methyl alcohol
C helium
D hydrogen
most interstellar molecules reveal their presence by radiating
A infrared wavelengths
B ultraviolet wavelengths
C x-rays
D radio wavelengths
the 21-centimeter line arises from which of the following?
A transitions between two very large orbitals of hydrogen.
B natural radioactivity of an unstable isotope of helium.
C a "flip" of the hydrogen electron spin from parallel to that of the nucleus to opposite that of the nucleus.
D complex molecules in interstellar dust clouds.
neutral hydrogen (hi) gas can be detected in interstellar space by its
A emission lines at millimeter wavelengths.
B absorption lines at optical wavelengths.
C 21-cm radio emission line.
D absorption at ultraviolet wavelengths.
neutral hydrogen may be detected between the stars because it emits
A a glow
B polarized light
C 21-cm radio signals
D x-rays
the component of the milky way galaxy which prevents us from seeing its center is
A hot hydrogen gas
B very cold hydrogen gas
C the light from nearby stars
D interstellar dust
which of the following cannot be used as observational evidence for the existence of interstellar gas and dust?
A the reddening of starlight
B the grouping of stars in clusters
C the detection of molecular clouds
D emission and reflection of nebulas around stars
we cannot see the nucleus of our galaxy because
A over 32,000 light years, the photons are too diffuse for us to receive a coherent picture
B it has been consumed by a gigantic black hole
C it is obscured by clouds of dust and gas
D it spins too fast
dust clouds, in interstellar space, may be recognized as
A brightly glowing nebulae
B dark regions which obscure light
C regions of very high temperature
D none of these
interstellar dust can be readily detected by its
A emission lines at 21 cm.
B absorption lines at millimeter wavelengths.
C blocking out of starlight.
D absorption at radio wavelengths.
one problem faced by astronomers in trying to figure out the structure of the galaxy is that
A there is no way to measure distances greater than about 3000 light years
B the galaxy looks the same in all directions from Earth
C we can only see a small region of the galaxy with optical telescopes because of interstellar dust
D the galaxy is always changing, so it's hard to pin down a single picture
the observational evidence for the existence of neutral hydrogen in the interstellar medium is
A the red color of the emission nebula.
B Balmer line emission in the spectra of gas clouds.
C x-ray emission from clouds surrounding hot, young stars.
D radio emission at a wavelength of 21-cm.
the interstellar medium is composed primarily of
A hydrogen and oxygen
B hydrogen and helium
C oxygen and helium
D dust particles
our ability to detect distant stars in our galaxy is limited because of
A absorption by dust in the galaxy
B the existence of strong 21-cm radiation in the galaxy
C the existence of many bright nebulae in the galaxy
D none of the above; there is no limit in our ability to detect distant star
in determining the galaxy's spiral arm structure, the main advantage that a radio astronomer has over an optical astronomer is that
A he/she can sleep at night
B radio telescopes are generally larger than optical telescopes
C radio waves penetrate interstellar dust more readily than light
D hydrogen can only be seen with a radio telescope
the interstellar medium is composed of
A stars
B planets and their associated satellites
C gas and dust
D micrometeorites
what effect does interstellar dust have on the magnitudes and colors of a star?
A dims the star only
B makes the star appear redder only
C makes the star dimmer and redder
D no change
how can interstellar dust be detected?
A dark regions of fewer stars in the milky way.
B stars that look redder than their spectral type.
C bluish nebulas around hot stars.
D all of the above.
E none of the above.
the best method of measuring the properties of interstellar gas is through the study of
A interstellar absorption lines
B interstellar magnetization
C interstellar reddening
D all of the above
which of the below is observational evidence that there is gas and dust between the stars?
A bright nebulas.
B dark rifts in the milky way.
C interstellar reddening.
D all of the above.
the sky is blue on a clear day because
A there is more blue light coming from the sun than any other color
B sunlight is absorbed by atoms in our atmosphere, which emit mostly blue light
C short wavelengths are more likely to be scattered by particles in out atmosphere
D air has a blue color when you look through enough of it
the temperature inside a typical interstellar cloud, before star begins, is about
A 3,000 k
B 300 k
C 10 k
D 0 k
a star seen through a cloud of dust
A will appear bluer than it would if no dust were in the way
B will appear redder than it would if no dust were in the way
C will have all its absorption lines shifted to shorter wavelengths
D will have all its absorption lines shifted to longer wavelengths
interstellar gas, through which starlight passes,
A significantly dims starlight
B produces interstellar absorption lines
C reddens the transmitted radiation
D has all the above effects on starlight
which of the following is not evidence of an interstellar medium?
A molecular bands in the spectra of cool stars
B lines of "cool" atoms in the spectra of hot stars
C reddening
D dark clouds
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