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general 🌙🪐 final
| Question | Answer |
|---|---|
| When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about: | how much energy the star gives off each second |
| When an astronomer measures a color index for a star, what is she measuring? | the difference between how bright a star looks at two different wavelength regions. |
| Which of the following types of star is the coolest (has the lowest surface temperature)? | m |
| If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars? | in the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum |
| Some objects in space just don't have what it takes to be a star (just like many hopefuls in Hollywood don't.) Which of the following is a "failed star", an object with too little mass to qualify as a star? | a brown dwarf |
| One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that: | brown dwarfs are able to do deuterium fusion in their cores, while planets can't |
| Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is | hydrogen |
| A star moving toward the Sun will show: | a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines) |
| Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its | proper motion |
| Which of the following can astronomers NOT learn from studying the spectrum of a star? | its surface temperature, whether it is a star the size of the Sun or a giant star, its motion toward or away from us, whether it is rotating slow or fast; all of these can be learned from studying the spectrum |
| Most of the stars we can see with the unaided eye from Earth are | more luminous (intrinsically brighter) than the Sun |
| Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly? | its mass |
| Two stars that are physically associated (move together through space) are called | binary stars |
| I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe | that the lines in its spectrum show a blue-shift |
| Stars on the main sequence obey a mass-luminosity relation. According to this relation, | luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass) |
| An H-R Diagram plots the luminosity of stars against their: | surface temperature |
| Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call: | the main sequence |
| Where on the H-R Diagram would we find stars that look red when seen through a telescope? | only on the right side of the diagram and never on the left |
| Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life? | fusing hydrogen into helium in their cores |
| A star that is quite hot and has a very small radius compared to most stars is called | a white dwarf |
| The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are farther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to | the same luminosity |
| Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by | bouncing radar beams off them |
| As astronomers use the term, the parallax of a star is | one half the angle that a star shifts when seen from opposite sides of the Earth's orbit |
| Which of the following will show the smallest parallax shift? | the star 51 Pegasi, about 50 lightyears away |
| A light curve for a star measures how its brightness changes with | time |
| How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter? | they can measure a regularly varying Doppler shift in the spectral lines |
| The higher the luminosity (intrinsic brightness) a Cepheid variable is, | the longer the period of its variations |
| If an astronomer wants to find the distance to a star that is not variable and is located too far away for parallax measurements, she can: | |
| Which type of star has the least amount of pressure in its atmosphere? | find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram |
| Which type of star has the least amount of pressure in its atmosphere? | supergiants |
| The luminosity class of a star tells an astronomer | whether the star is a supergiant, a giant, or a main-sequence star |
| Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud? | when massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form |
| Why is it so difficult for astronomers to see new stars in the process of birth? | birth happens very quickly, so it is hard to "catch" stars "in the act" |
| Astronomers call a ball of matter that is contracting to become a star | a protostar |
| Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star? | when nuclear fusion reactions begin inside its core |
| Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence? | a star ten times the mass of our Sun |
| Which of the following is NOT one of the reasons planets around other stars are so difficult to detect? | planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life |
| What observations about disks of dusty material around young stars suggest that planets may be forming in such disks? | the disks show lanes that are empty of dust within them |
| Planets in the habitable zone of their stars: | are at a temperature where water can exist as a liquid |
| Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters" | must have formed close to their stars, but only billions of years after the star formed |
| The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun? | it would be significantly closer to Proxima Centauri than ours is to the Sun |
| Why do all stars spend most of their lives on the main sequence? | because the fuel for energy production in this stage of the star's life is hydrogen; and that is an element every star has lots and lots of |
| How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on | its mass |
| Biologists tell us that life on Earth took billions of years to evolve into astronomy students and other examples of intelligent life. If we want to search for planets with intelligent life-forms that evolved over the same period of time that we did, what | O and B type stars |
| When the outer layers of a star like the Sun expand, and it becomes a giant, which way does it move on the H-R diagram? | toward the lower right |
| A type of star cluster that contains mostly very old stars is | a globular star cluster |
| On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age? | the point on the main sequence where stars begin to "turn off" - to move toward the red giant region |
| The oldest structures in our Galaxy turn out to be | globular clusters |
| Really massive stars differ from stars with masses like the Sun in that they | can fuse elements beyond carbon and oxygen in their hot central regions |
| If most stars are low-mass stars, and low-mass stars typically eject a planetary nebula, why then do astronomers see relatively few planetary nebulae in the sky? | planetary nebulae expand rapidly and soon become too faint to be visible |
| If star with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe? | heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle |
| Which of the following is a characteristic of degenerate matter in a white dwarf star? | the electrons get as close to each other as possible and resist further compression |
| A white dwarf, compared to a main sequence star with the same mass, would always be: | smaller in diameter |
| Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we ca | some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars |
| The most stable (tightly bound) atomic nucleus in the universe is | iron |
| In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into a neutron and a | neutrino |
| If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604? | the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy |
| Elements heavier than iron can be created during | a supernova explosion |
| Astronomer have concluded that pulsars are | rotating neutron stars |
| In the model that astronomers have developed for pulsars, why do they suggest that there must be two beams of energy coming from the pulsar? | because neutron star beams come out of the north and south poles of a magnetic field |
| Astronomers now have a good idea for explaining how the short-duration gamma-ray bursts might come about. Which of the following is part of their explanation? | these bursts come from the clouds of comets that surrounds our solar system |
| Our Milky Way Galaxy is what type of galaxy? | spiral |
| Which type of galaxy is observed to contain mostly older stars? | elliptical |
| Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies? | their shape |
| Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers? | they are (for galaxies) very close to us, so they are easy to study |
| Which of the following statements about the different types (shapes) of galaxies is correct? | collisions and mergers between galaxies can sometimes change a galaxy's type (shape) |
| A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make? | obtain the speed at which stars or gas near the outer regions of the galaxy are moving around |
| Compared to the mass of our own Milky Way Galaxy, the total mass we estimate for the Andromeda Galaxy is | somewhat bigger |
| What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)? | finding the redshift and using Hubble's Law |
| Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances? | type la supernovae |
| The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that: | this particular nearby galaxy is moving toward us |
| The standard bulbs (standard candles) that made it possible for astronomers to discover the acceleration in the expansion of the universe were | Type la supernovae |
| Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is | O about 13.8 billion years |
| In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a red-shift? | as space stretches, the waves of radiation in space also stretch and their wavelength increases |
| Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these: | carbon |
| Which of the following is pretty good evidence that the universe began with a Big Bang? | the 3-degree cosmic microwave background radiation |
| Where in space did the expansion of the universe begin? | everywhere at once |
| Which of the following statements about dark matter is FALSE: | astronomers have a pretty good idea what the dark matter is made of |
| According to our textbook, roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy? | 95 percent |
| The model of the universe that involves an enormous increase of scale during a very short time in the early universe is called: | the inflationary universe model |
| Scientists looking at an overview of physics today understand that there are four forces that govern all action in the universe. These four forces are the strong nuclear force, the weak nuclear force, electro-magnetism and | gravity |
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