Astronomy today Chapter 18 The interstellar medium – Flashcards
Unlock all answers in this set
Unlock answersquestion
What wavelengths can penetrate the dark nebulae?
answer
They can be penetrated only with longer wavelengths such as radio and infrared.
question
Why are dark dust clouds largely misnamed?
answer
They contain much more gas than dust.
question
Neutral hydrogen is most obvious in the electromagnetic spectrum at:
answer
21 cm in the radio region.
question
What are the very cold (about 20-K), dense clouds of gas thought to be the most massive objects in the Galaxy called?
answer
molecular clouds
question
Spectra of stars often show narrow absorption lines from interstellar matter. What type of interstellar matter produces these?
answer
neutral gas
question
The relative density of dust to gas is least in which place?
answer
the atmosphere of Earth
question
Most interstellar clouds are
answer
much bigger than our solar system
question
The overall dimming of starlight by interstellar matter is called
answer
extinction
question
Which statement is true about the interstellar medium?
answer
We know more about the gas than the dust
question
What is the primary visible color of an emission nebula?
answer
red due to ionized hydrogen atoms
question
Interstellar absorption lines are narrow primarily because:
answer
the matter is at a low temperature, atoms are almost still.
question
Charles Messier mapped the night sky and identified many objects now known to be emission nebulae in his search for objects that might be confused with
answer
comets
question
How can interstellar dust block starlight in spite of its extremely low density?
answer
The grain size of the dust is comparable to the wavelength of the light blocked, so scattering of light is possible. Also, clouds are so vast that even at low density they contain a lot of dust.
question
A reflection nebula is caused by
answer
starlight scattered by dust particles.
question
What effect does even thin clouds of dust have on light passing through them?
answer
It dims and reddens the light of all more distant stars.
question
Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear
answer
redder
question
Unlike the ultraviolet photons originally emitted by the embedded stars of an emission nebula, the photons emitted by the recombination of electrons with atoms
answer
escape the nebula
question
Emission nebulae like M42 occur only near stars that emit large amounts of
answer
ultraviolet radiation
question
Which of these is not a consequence of dust in the interstellar medium?
answer
red light from the emission nebulae
question
Some regions along the plane of the Milky Way appear dark because
answer
stars in that region are hidden by dark dust particles.
question
Astronomers use roman numerals to indicate the ionization state of a gas. Ionized hydrogen is indicated by which of the following symbols?
answer
HII
question
Interstellar gas is composed of
answer
90% hydrogen, 9% helium By weight
question
Complex molecules is space are found
answer
Inside dense dust clouds
question
The average temperature of the typical dark dust cloud is about
answer
100 K
question
Ionization of hydrogen in HII region is most visible at
answer
653.3 nm
question
Some regions along the plane of the Milky Way appear dark because
answer
Stars in that region are hidden by dark particles
question
Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear
answer
Redder
question
Neutral hydrogen is most obvious in the electromagnetic spectrum at
answer
21 cm in the radio region
question
The local Bubble was probably created by
answer
A nearby supernova perhaps 300,000 years ago, brighter than the full moon
question
The density of interstellar dust is very low, yet it still blocks starlight because
answer
The dust particles are about the same size as a lightwave they absorb
question
When an electron in H changes it's Spin from the same to the opposite direction as the Proton it
answer
Emits a Radio wave photon
question
Which shape describe the shape of dust partcles, based on polarization of light
answer
Rod like
question
The ___________of light passing through thin dust clouds lets us map the galaxy's magnetic field
answer
Polarization
question
What feature of interstellar dust is inferred by the polarization of starlight?
answer
It's shape
question
A large gas cloud in the interstellar medium that contain several type O and B stars would appear to us as
answer
An emission nebula
question
The spectra of interstellar gas clouds show that they have the same basic composition
answer
Stars
question
A reflection nebula is caused by
answer
Starlight scattered by dust particles
question
In which wavelength have the birth of new stars have been Best mapped recently?
answer
Infrared
question
Emission nebula take up about how much of the Milky Way galaxy?
answer
1%
question
What two things Are needed to create an emission nebulae
answer
Hot stars and interstellar gas, particularly hydrogen
question
In the Milky Way galaxy, gas and dust are found
answer
Everywhere
question
Unlike the ultraviolet photons originally emitted by the embedded it starts of an emission nebula, if photons emitted by the recombination of electrons with Atoms
answer
Escape the nebula
question
Why are dark dust clouds largely misnamed?
answer
They contain much more gas than dust
question
Why is 21 cm radiation so important to the study of interstellar matter and the galaxy?
answer
Emitted by hydrogen, it passes through interstellar dust and lets us map ten entire galaxy
question
The local Bubble is
answer
About 100 pc. across and transparent to extreme ultraviolet radiation
question
Emission nebula like M42 Occur only near stars that Emit large amounts of
answer
Ultraviolet radiation
