Astronomy & Astrophysic

Q: The spectral lines of a star indicate ionized helium is prominent, yet the star appears orange in color. Explain the problem with this and offer an explanation.

Q: Why can radio waves get through the dust clouds, but light is blocked?

Q: Contrast the chemical composition of interstellar gas with that of interstellar dust.

Q: In general, Globular clusters are ________ and ________ than open clusters.

Q: In typical globular clusters, the brightest stars are ________.

Q: The Pleiades (or Seven Sisters) an example of an ________.

Q: Bright blue stars are typical of young ________ star clusters.

Q: A protostar of one-half solar mass would reach the main sequence in ________ time than it took our own Sun.

Q: A star of five solar masses would reach the main sequence much ________ than our Sun.

Q: ________ objects are found at opposite ends of the bi-polar jets expelled in the protostar's T-Tauri phase.

Q: In its ________ stage, the new protostar's solar winds will form bi-polar jets as the star's magnetic field intensifies.

Q: A photosphere appears on a protostar near the end of stage ________.

Q: Herbig-Haro objects at opposite ends of bi-polar jets can span a ________ across.

Q: Compared to a hydrogen atom where the proton and electron both have spin in the same direction, an atom where they spin in opposite directions will have ________ energy.

Q: The interstellar gas in our portion of the Galaxy is about ________ K in temperature.

Q: Generally, the densest parts of the interstellar medium are the ________.

Q: Molecules are found only in the ________ clouds of the interstellar medium.

Q: While many elemental spectral lines are visible, almost all molecular lines lie in the ________ portion of the spectrum, since they are at much lower energy.

Q: Neutral hydrogen can be detected because its electron occasionally ________ its spin and creates the 21-cm emission line for radio observers.

Q: Red sunset, red lunar eclipses, blue skies, and reflection nebulae are all the result of the ________ of visible light off tiny dust particles.

Q: A reflection nebula appears blue because it scatters the ________ light of the stars near it.

Q: Emission nebulae occur only near stars that emit large amounts of ________ electromagnetic radiation.

Q: Almost all of the complex molecules found in space are based on ________ atoms.

Q: A region of ionized gas and dust, with imbedded hot young stars, is an ________.

Q: The gas in an HII region is ________ hydrogen.

Q: Neutral hydrogen clouds appear ________ when viewed visually.

Q: Interstellar reddening and extinction are due to ________ in the interstellar medium.

Q: Of all forms of electromagnetic energy, ________ radiation gives us the least access to our entire Milky Way Galaxy.

Q: Which of these would typically be among the brightest stars in an ancient globular cluster? A) O3 B) B3 C) A4 D) K3 E) M5

Q: Most stars in our part of the Galaxy are formed A) alone. B) in open clusters of a few dozen. C) in associations of thousands of stars across a spiral arm of the Galaxy. D) in globular clusters of millions of stars. E) in a singular event just after the Big Bang.

Q: Why are star clusters ideal "laboratories" for stellar evolution? A) The combined light of all the stars makes them easier to see. B) Like our Sun, they lie in the plane of the Milky Way. C) Their stars are all about the same age, composition, and distance from us. D) Their stars are all about the same mass and temperature. E) Their stars are all the same composition and stage in evolution.

Q: Which of these would typically be the brightest star in a young open cluster? A) G2V B) B1V C) A2Ib D) K3II E) M3Ia

Q: Which is characteristic of globular star clusters? A) old age and hundreds of thousands of stars, only about 30 ly wide B) no remaining main sequence stars, but millions of white dwarfs C) only brown dwarfs in a yellow ball 100 ly across D) bright blue main sequence stars, and thousands of them E) a mix of old and young stars, about 100,000 ly across

Q: What are the characteristics of an open cluster of stars? A) mostly found above and below the galactic plane B) old age and millions of members C) a few hundred, mostly main-sequence stars D) All stars are much more massive than our Sun. E) All stars are about the same age and luminosity.

Q: All globular clusters in our Milky Way are about how old? A) less than a million years B) ten-fifty million years old C) one to three billion years old D) around ten billion years old E) a variety of ages, from newly born to twenty billions years old

Q: Approximately how many brown dwarfs are believed to exist in the Milky Way galaxy? A) 100,000 B) one million C) one billion D) one hundred billion E) ten trillion

Q: A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of 4 million K will become a A) black hole. B) brown dwarf. C) black dwarf D) T-Tauri star. E) stage 1 protostar.

Q: How long does it take an M-type star to reach the main sequence, compared to a solar-type star? A) a tenth as long B) about the same, 30 million years C) about twice as long D) about twenty times longer E) longer than the age of the Galaxy

Q: A cloud fragment too small to collapse into a main sequence star becomes a A) white dwarf. B) pulsar. C) T-Tauri object. D) brown dwarf. E) planet of another star.

Q: The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its A) chemical composition. B) magnetic field. C) spin. D) mass. E) molecular composition.

Q: On an H-R diagram, a protostar would be A) above and to the right of the main sequence. B) below and to the left of the main sequence. C) below and near the right side of the main sequence. D) above and near the upper left of the main sequence. E) on the main sequence at the extreme lower right.

Q: Which statement about the stages of starbirth is false? A) At stage 1, only the cloud exists. B) By stage 3, the star has formed a photosphere. C) nuclear reactions begin in the core by stage 4. D) The T-Tauri wind is prevalent in stage 5. E) By stage 7, the star has reached the main sequence.

Q: At what core temperature does hydrogen begin to fuse to helium? A) 3,000 K B) 5,800 K C) 1 million K D) 10 million K E) 100 million K

Q: During the T-Tauri phase of a protostar, it A) begins a period of reduced activity. B) expands dramatically. C) lies on the main sequence. D) may develop very strong winds. E) changes its spin direction.

Q: A newly formed protostar will radiate primarily at which wavelength? A) visible light B) X-ray C) infrared D) ultraviolet E) radio

Q: When an electron in a hydrogen atom changes its spin from the same to the opposite direction as the proton, it A) emits an X-ray photon. B) absorbs a radio wave photon. C) emits a radio wave photon. D) absorbs a visible light photon. E) neither emits nor absorbs a photon.

Q: Interstellar dust clouds are best observed at what wavelength? A) Radio and infrared B) visible only C) UV and infrared D) Radio and X-ray E) Visible and UV

Q: The average temperature of the typical dark dust cloud is about A) 0 K. B) 2.73 K. C) 100 K. D) 3,000 K. E) 6,000 K.

Q: Neutral hydrogen atoms are best studied from their energy given off as A) red hydrogen alpha emission, at 656.3 nm. B) 121.3 nm as Lyman alpha emission in the UV. C) 21-cm waves in the radio region. D) 0.2 nm as X-rays. E) Neutral hydrogen gives off no detectable radiation, since it is cold, not hot.

Q: What information does 21-cm radiation provide about the gas clouds? A) their motion B) their distribution C) their density D) their temperature E) all of these

Q: Complex molecules in the interstellar medium are found A) uniformly throughout the disk of the Galaxy. B) scattered evenly throughout the universe, a product of the Big Bang itself. C) only around the supergiant stars like Betelgeuse that make their heavy atoms. D) primarily in the dense dust clouds. E) on the surfaces of the coolest class K and M stars only.

Q: Why are dark dust clouds largely misnamed? A) The cloud is an illusion, for the dust is evenly distributed around the Galaxy. B) Dust clouds do radiate energy, but not as much light as the stars do. C) It is ice, not dust, which make them look dark. D) They contain much more gas than dust. E) All of the above are correct.

Q: The most common molecule in a molecular cloud is A) methane, CH4. B) molecular hydrogen, H2. C) carbon monoxide, CO. D) water, H2O. E) ammonia, NH3.

Q: Which of these is not a consequence of dust in the interstellar medium? A) reddening of stars' light that passes through the dust B) blue reflection nebulae around the Pleiades C) red light from the emission nebulae D) the dark nebulae that block 90% of the Milky Way from us visually E) terrestrial planets like our own

Q: A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as A) a dark nebula. B) an emission nebula. C) bright blue. D) a reflection nebula. E) a dark patch against a bright background.

Q: What two things are needed to create an emission nebula? A) interstellar gas and dust B) hydrogen fusion and helium ionization C) cool stars and much interstellar dust D) hot stars and interstellar gas, particularly hydrogen E) hydrogen gas and carbon dust

Q: The gas density in an emission nebula is typically about how many particles per cc? A) dozen B) hundred C) thousand D) hundred thousand E) million

Q: The density of interstellar dust is very low, yet it still blocks starlight because A) it is so cold it absorbs higher energy photons. B) there is 100 times more opaque gas than dust present in the interstellar medium. C) the dust particles are about the same size as the light waves they absorb. D) the dust particles are irregular in shape. E) ice particles reflect all light back toward their stars, not toward us.

Q: What is the primary visible color of an emission nebula? A) black, because of dust B) blue from the scattering of light off the tiny molecules C) blue due to ionized helium atoms D) red due to the HÎ± line of hydrogen E) red because of reddening by dust

Q: Emission nebulae like M42 occur only near stars that emit large amounts of A) visible light. B) microwaves. C) ultraviolet radiation. D) infrared heat. E) X-rays and gamma rays.

Q: The spectra of interstellar gas clouds show that they have the same basic composition as A) interstellar dust. B) Earth's atmosphere. C) stars. D) asteroids. E) the Martian polar caps.

Q: Which statement is true about the interstellar medium? A) Gas contains a lot of carbon atoms. B) Dust blocks the longest electromagnetic wavelengths. C) Gas obscures the light from distant stars. D) We know more about the gas than the dust. E) Dust is spread uniformly through the galaxy.

Q: Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear A) bluer. B) brighter. C) redder. D) larger. E) to have a higher radial velocity.

Q: Some regions along the plane of the Milky Way appear dark because A) there are no stars in these areas. B) stars in that region are hidden by interstellar gas. C) stars in that region are hidden by dark dust particles. D) many brown dwarfs in those areas absorb light, which they turn into heat. E) many black holes absorb all light from those directions.

Q: Which statement about dark dust clouds is true? A) Hydrogen and helium are the chief absorbing and scattering agents. B) They block the vast majority of radio waves from our Galaxy. C) They can be penetrated only with longer wavelengths such as radio and infrared. D) They comprise the majority of the mass of the Galaxy. E) They can be penetrated only with shorter waves, such as UV and X-ray.

Q: What happens to light passing through even thin clouds of dust? A) The light that passes through them is blue shifted due to the cloud's approach. B) It dims and reddens the light of all more distant stars. C) Even a little can completely block all light, such as the Horsehead Nebula. D) Its motion causes the light of stars beyond to twinkle. E) Its motion causes all light to be red shifted as it passes through these clouds.

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