Astronomy Exam 3

How far away would a star with a parallax of 0.2 arcsec be from us? 2 parsecs 0.2 parsecs we need more information to answer this question 5 parsecs 0.5 parsecs

5 parsecs

When a single star with a mass equal to the Sun dies, it will become a pulsar burster neutron star black hole white dwarf

white dwarf

Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence? O G every star spends about the same number of years on the main sequence A K

K

Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)? Such planets are red in color, and Kepler's cameras could not see red objects Such planets make dips in the light of the star that are too small for Kepler to detect Such planets always take longer to orbit their stars than the time the mission lasted Such planets are only ever detectable using the Doppler shift method Astronomers believe that planets smaller than Mars could not exist

Such planets make dips in the light of the star that are too small for Kepler to detect

A type of star cluster that contains mostly very old stars is a galaxy a stellar association a globular star cluster an HII region an open cluster

a globular star cluster

The Orion Nebula is a large cloud of gas and dust illuminated by the light of newly formed stars within it the remnant of a star that exploded several thousand years ago a distant galaxy of stars and raw material an illusion caused by activity in the Earth's upper atmosphere a small disk of gas and dust surrounding a single star that was recently formed

a large cloud of gas and dust illuminated by the light of newly formed stars within it

A star moving toward the Sun will show: a significant increase in its apparent brightness (magnitude) no change that can be measured with our present-day instruments a shift in the spectral lines toward the red end (as compared to the laboratory positions of these lines) more and more helium lines as it approaches us a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

Elements heavier than iron can be created during: the main sequence the red giant phase a supernova explosion the planetary nebula phase the big bang

a supernova explosion

The event in the life of a star that begins its expansion into a giant is it reaches the stage that astronomers call the zero-age main sequence almost all the hydrogen in its core that was hot enough for fusion has been turned into helium the star's internal structure reaches equilibrium for the first time in its life the core reaches a temperature of ten million degrees as much as 90% of the star explodes violently

almost all the hydrogen in its core that was hot enough for fusion has been turned into helium

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)? along the bottom (the horizontal axis) only in the red giant region H-R diagrams have nothing to say about spectral types only on the main sequence along the right (vertical axis)

along the bottom (the horizontal axis)

Planets in the habitable zone of their stars: are always the planets closest to the star are so far from their stars that it is very difficult to discover them cannot exist around stars that are red dwarfs (spectal type M) are at a temperature where water can exist as a liquid are also called hot Jupiters

are at a temperature where water can exist as a liquid

Why are astronomers much more interested in the luminosity of a star than its apparent brightness? because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a star's chemical make-up because the luminosity tells us how much energy the star emits, while apparent brightness only tells us how bright it happens to look from Earth you can't fool me, there is no difference between luminosity and apparent brightness; they are merely different terms for the same property of a star because luminosity can be measured exactly, but apparent brightness can only be roughly estimated because luminosity can tell us how bright it is inside the star's core, while apparent brightness only tells us about its outside layers

because the luminosity tells us how much energy the star emits, while apparent brightness only tells us how bright it happens to look from Earth

Why did it take astronomers until 1838 to measure the parallax of the stars? because most stars are too faint to see without a good telescope because detecting parallax requires measuring a spectrum, which only became possible in the 1830's because no one before then could conceive of the Earth moving around the Sun because cepheid variable stars had not been discovered earlier because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope

because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope

Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen? because all such elements become radioactive and their nuclei break apart rather quickly because all such stars explode before they can make any other elements because the cores of such stars get too hot for further types of fusion to be able to happen because there are no elements heavier than those two; they are the heaviest nuclei in nature because they just cannot get hot enough for the fusion of heavier nuclei

because they just cannot get hot enough for the fusion of heavier nuclei

Which color star is likely to be the hottest? red green orange blue-violet yellow

blue-violet

Really massive stars differ from stars with masses like the Sun in that they they are significantly less luminous after the main sequence stage is over can fuse elements beyond carbon and oxygen in their hot central regions are no longer forming in the Galaxy; they only formed very early in the Galaxy's history do not really go through a main sequence stage in their lives go through all the stages of their lives more slowly

can fuse elements beyond carbon and oxygen in their hot central regions

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life? you can't fool me; so many stars are on the main sequence that there is no special stage in a star's life that can be identified with it dying fusing hydrogen into helium in their cores forming from a reservoir of cosmic material letting go of a huge outer layer

fusing hydrogen into helium in their cores

Astronomers have noticed that the visible filaments in the Crab Nebula are moving toward us at great speed. How can they know about motions like this? from the HR diagram from the color of the nebula's continuous radiation from the spacing of the pulsar pulses from the Doppler shift in the line radiation from the nebula from the width of the pulsar pulses

from the Doppler shift in the line radiation from the nebula

If stars 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 heavier elements are made in the cores of planets that are molten and hot when they form heavier elements are made in the proto-planetary disks that accompany many newly forming stars these heavier elements were made in the Big Bang at the time the universe began, and have been part of the universe ever since this is an unsolved problem in astronomy; no one knows

heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle

A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use to observe it? ultraviolet x-rays gamma-rays very long wavelength radio waves infrared

infrared

The most stable (tightly bound) atomic nucleus in the universe is: carbon technetium uranium iron hydrogen

iron

Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is: radiating most of its energy in the infrared region of the spectrum it could be any of these; there is no way to tell which answer is right by just looking at the star very far away very low luminosity partly obscured by a cloud

it could be any of these; there is no way to tell which answer is right by just looking at the star

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500oK). How can this be? it must be brown dwarf and not a regular star it must be quite large in size it must be a main sequence star it must be quite small in size this must be an error in observations; no such star can exist

it must be quite large in size

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 in the same position as our habitable zone, but be much thinner this question can't be answered until we send a probe to Proxima Centauri it would be in the same position as our habitable zone, but be much wider it would be significantly closer to Proxima Centauri than ours is to the Sun it would be significantly further away from Proxima Centauri than our is to the Sun

it would be significantly closer to Proxima Centauri than ours is to the Sun

Astronomers must often know the distance to a star before they can fully understand its characteristics. Which of the following properties of a star typically requires a knowledge of distance before it can be determined? its temperature its luminosity all of these its radial velocity its apparent brightness

its luminosity

When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall? the size of the disk around it whether it is located on the outer regions or the central regions of the molecular cloud that gave it birth the speed and direction of its rotation its mass the fraction of its atmosphere that consists of hydrogen

its mass

The most common kinds of stars in the Galaxy have low luminosity compared to the Sun diameters thousands of times greater than the Sun's enormous masses compared to the Sun spectra that show they contain mostly carbon a dozen or more stars in close orbit around them

low luminosity compared to the Sun

What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun? search for the presence of metallic and rocky elements in the spectrum of the star measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star look for a small dip in the light of the star when the planet crosses its disk block out the light of the star and take a photograph of the fainter planet measure the position of the star on the sky very carefully over many years and search for small wiggles in its position due to the gravitational pull of a planet

measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star

How are globular clusters distributed in our Milky Way Galaxy? completely randomly: you never know where we will find one only in the main spiral disk of the galaxy mostly in a large spherical halo (or cloud) surrounding the flat disk of the Galaxy only in the very center of the Galaxy, really crowded together where the giant molecular clouds are found

mostly in a large spherical halo (or cloud) surrounding the flat disk of the Galaxy

Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look three times fainter nine times fainter nine times brighter just as bright as A three times brighter

nine times fainter

The big surprise about the first planet discovered around another regular star was that it had a spectrum which indicated it was made of elements we never find on Earth had a mass greater than that of most stars was inhabited by intelligent creatures orbited so close to its star it took only 4 days to go around was smaller than Mercury or Pluto in our own solar system

orbited so close to its star it took only 4 days to go around

An astronomer is interested in a galaxy called M31, the nearest galaxy that resembles our Milky Way. It is about 2 million light-years away. Which technique would be able to give us a distance to this galaxy? radar reflections parallax period-luminosity relation for Cepheid variables there is no way at present to get a distance to an object so far away Kepler's laws

period-luminosity relation for Cepheid variables

A white dwarf, compared to a main sequence star with the same mass, would always be: younger in age smaller in diameter the same size more massive redder in color

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 can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained? stars less massive than 1.4 times the mass of the Sun go through the white dwarf stage in their lives before they become main sequence stars stars lose a lot of mass on their way to becoming white dwarfs; and so the white dwarfs could have started out as quite massive stars the lower the mass of a star, the more quickly it goes through each stage of its life clusters often contain stars of very different ages astronomers can think of no way to explain this problem; it has them completely baffled

stars lose a lot of mass on their way to becoming white dwarfs; and so the white dwarfs could have started out as quite massive stars

How do fragile structures like acetaldehyde (CH3CHO) molecules survive in the harsh environment of interstellar space? Why are they not destroyed by high-energy radiation from stars? such molecules are protected by the presence of hot interstellar hydrogen such molecules are found only where very cool stars are present, that's why they are so very rare in the Galaxy such molecules are only found in the shadows of the stars such molecules are found only in dense clouds that have a lot of dust; the dust keeps the radiation from hot stars from reaching the molecules such molecules are found only on planets or comets, not in space

such molecules are found only in dense clouds that have a lot of dust; the dust keeps the radiation from hot stars from reaching the molecules

The telescope that allowed astronomers to discover most of the planets found with the transit method was called the Keck Telescope just about any telescope can show us many, many planet transits the Kepler mission the Very Large Array of radio telescopes the Hubble Space Telescope

the Kepler mission

When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough? the heat comes from the outer layers of the star, which are much hotter than the core as the star expands, all the layers heat up the core is collapsing under its own weight and heating up from the compression; this heats the next layer up the heat comes from the fusion of carbon in the core, which starts right away this is an unsolved problem in astronomy, but something must be heating that layer, since we observe red giants out there

the core is collapsing under its own weight and heating up from the compression; this heats the next layer up

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 all the explosions happened in that part of the sky which is only visible from the Earth's southern hemisphere, and we do not have any large telescopes down there most supernova explosions produce only high-energy gamma-rays and very little light actually, there have been supernova explosions observed, but there is a government conspiracy to keep ordinary citizens from learning about them we have been very unlucky; there have been far fewer explosions than average recently

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

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 the disks show evidence of very strong winds coming from the star the disks give off x-rays and gamma-rays characteristic of small planets the disks are making the stars "wiggle" -- move back and forth across the sky -- in a way that can be observed even with small telescopes radio telescopes have revealed transmissions from the disks that include evidence of advanced civilizations

the disks show lanes that are empty of dust within them

If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today? the first generation stars all live their lives much more slowly than stars today (so they last a long time) the first generation stars contain little or no elements heavier than helium the first generation stars exploded as soon as they formed the first generation stars never become red giants I disagree; I think first generation stars will be like stars forming today in all ways

the first generation stars contain little or no elements heavier than helium

You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler Effect. A few lines, however, do not shift at all, but remain at the same wavelength. How can we explain the behavior of the non-shifting lines? there is a star in the system which is not moving at all: it is just sitting there the lines come from interstellar matter between us and the star, not from the stars themselves there are huge clouds of dust just behind this star system from our perspective there is a planet orbiting the stars in the system there is no explanation of this behavior: it is an unsolved mystery in science

the lines come from interstellar matter between us and the star, not from the stars themselves

Among interstellar clouds, the hotter the cloud, the the lower the density of particles in it the smaller the diameter of the cloud must be the more likely it is to contain vast quantities of complex molecules less likely it is to contain ionized atoms the higher the density of particles in it

the lower the density of particles in it

A neutron star is as dense as the nucleus of an atom a white dwarf star water styrofoam the center of the Earth

the nucleus of an atom

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 number of M stars on the main sequence the lowest luminosity star that is visible in the cluster the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region the coolest surface temperature for a star that they can measure how high up on the main sequence M type stars are found

the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region

When a star undergoes a nova explosion, it may return to its "quiet state" and later become a nova again. What would allow a nova explosion to happen to a star more than once? the star that goes nova collides with several stars in a star cluster the star that goes nova has a number of massive planets around it which fall in a nova explosion happens each time a neutron star rotates to face us, and that happens every century or so the star that goes nova has a companion star near it, which dumps material onto the first star and continues to do so even after the first nova explosion the star that goes nova has an iron catastrophe in its core and then another step in the fusion of heavy elements producer another explosion

the star that goes nova has a companion star near it, which dumps material onto the first star and continues to do so even after the first nova explosion

Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us? actually, this is just an optical illusion; all stars are really the same brightness these stars vary in brightness (flashing brighter and dimmer) and are thus easier to notice all the brightest stars are red, and red color is much easier to see against the black night sky these stars are intrinsically so luminous that they can easily be seen even across great distances we see them in crowded regions of stars, which give us the impression that the stars there are brighter than they really are

these stars are intrinsically so luminous that they can easily be seen even across great distances

The dust in the dust clouds in interstellar space consists of atomic gas tiny solid grains molecular gas pieces of ice ranging from several meters to a kilometer in diameter none of these

tiny solid grains

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram? downwards to the left upwards stars don't move on the H-R diagram to the right

to the left

Some of the interstellar gas in our Galaxy has been heated to millions of degrees, a temperature that surprised astronomers when it was first discovered. How do we now think that gas between stars gets that hot? gas gets to be this hot when hydrogen atoms flip their spin and give off 21-cm radiation very powerful shock waves from exploding stars heat the gas they come into contact with such gas is heated by the radiation given off by complex molecules in clouds astronomers have no idea how gas gets this hot; this is an unsolved mystery in astronomy any gas close to a star will naturally get that hot

very powerful shock waves from exploding stars heat the gas they come into contact with

What is the baseline that earth-bound astronomers use to measure the parallax (the distance) of the nearest stars? the diameter of the Earth the distance between observatories in Greenwich, England and Washington, DC no one can measure parallax for the stars; only for planets in our solar system ½ the diameter of the Earth's orbit around the Sun the distance between the Earth and the Moon

½ the diameter of the Earth's orbit around the Sun