Astronomy Chapter 18 Answers – Flashcards
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What is the average temperature of interstellar gas and dust
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100 K
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Spectra of stars often show narrow absorption lines from interstellar matter. What type of interstellar matter produces these?
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neutral gas
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What effect does dust have on visible light passing through it?
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It dims and reddens it
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Interstellar gas is composed mainly of
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hydrogen
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The "Local Bubble" is
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About 100 pc. across and transparent to extreme ultraviolet radiation
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The most famous emission nebula of the winter sky is
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M-42, the Orion Nebula.
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Emission nebulae like M-42 occurs only near stars that emit large amounts of
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ultraviolet radiation
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Which two ingredients are needed to make an emission nebula or H II region
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hot O-B stars and interstellar gas
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Interstellar absorption lines are narrow primarily because:
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the matter is at a low temperature, atoms are almost still.
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What do "forbidden" lines reveal about interstellar space?
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The density or pressure of this gas is much lower than can be produced in a laboratory.
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The density of interstellar dust is extremely low, but it can block starlight because:
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interstellar dust particles are equal in size to wavelengths of visible light.
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Which of the following describes the shape of dust particles, based on polarization of light?
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rodlike
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Why are dark dust clouds largely misnamed?
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They contain much more gas than dust.
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Some regions of the Milky Way's disk appear dark because:
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stars in that direction are obscured by interstellar dust
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In which wavelengths have the births of new stars been best mapped recently?
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infrared
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The __________ of light passing through thin dust clouds lets us map the Galaxy's magnetic field.
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polarization
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Neutral hydrogen is most obvious in the E-M spectrum at:
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21 cm in the radio region.
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What color is a H I region?
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colorless; it emits in the radio region
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What information does 21-centimeter radiation provide about the gas cloud that emitted it?
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radial velocity, density, and temperature
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The most common molecule in a molecular cloud is:
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molecular hydrogen, H2.
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Complex molecules in space are found:
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inside dense dust clouds.
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Unlike atoms, molecules can:
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a. rotate b. vibrate (both A and B)
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radio radiation emitted when an electron in the ground state of a hydrogen atom flips its spin to become anti-parallel to the spin of the proton in the nucleus
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21 cm radiation
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a large cloud, often many parsecs across, which contains gas and dust in a ratio of about 1012 gas atoms for every dust particle
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dark dust cloud
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collection of molecular clouds that spans as much as 50 parsecs and may contain enough material to make millions of Sun-size stars
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Molecular cloud complex
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a lane of dark, obscuring interstellar dust in an emission nebula or galaxy
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dust lane
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a cold, dense interstellar cloud which contains a high fraction of molecules
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molecular clouds
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an interstellar dust particle, roughly in size, comparable to the wavelength of visible light
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dust grain
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dimming of starlight by interstellar matter, which tends to scatter higher-frequency
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reddening
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the alignment of the electric fields of emitted photons, which are generally emitted with random orientations
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polarization
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general term used for any "fuzzy" patch on the sky, either light or dark
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nebula
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the matter between stars, composed of two components, gas and dust, intermixed throughout all of space
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interstellar medium
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the dimming of starlight as it passes through the interstellar medium
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extinction
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a glowing cloud of hot interstellar gas. The gas glows as a result of one or more nearby young stars which ionize the gas
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emission nebula
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essay
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Cats eye nebula. It is located in the northern part in the constellation of Draco. It was formed 1,000 years ago. It is 3,300 light years away from earth, but only .2 light years across in size. The ra is 17h 58 mins and 33 seconds
