EXAM 3 NJIT Phys 202 Gately

1. 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

a. three times brighter

b. nine times brighter

c. nine times fainter

d. three times fainter

e. just as bright as A

c. nine times fainter

2. Using a good pair of binoculars, you observe a section of the sky where thereare stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is:

a. very far away

b. very low luminosity

c. radiating most of its energy in the infrared region of the spectrum

d. partly obscured by a cloud

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

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

3. Why are astronomers much more interested in the luminosity of a star than its

apparent brightness?

a. because luminosity can be measured exactly, but apparent brightness can only be roughly estimated

b. 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

c. 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

d. because luminosity can tell us how bright it is inside the star's core, while apparent brightness only tells us about its outside layers

e. 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

b. 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

4. A star moving toward the Sun will show:

a. a shift in the spectral lines toward the blue end (as compared to the laboratory

positions of these lines)

b. a significant increase in its apparent brightness (magnitude)

c. more and more helium lines as it approaches us

d. a shift in the spectral lines toward the red end (as compared to the laboratory

positions of these lines)

e. no change that can be measured with our present-day instruments

a. a shift in the spectral lines toward the blue end (as compared to the laboratory

5. Which color star is likely to be the hottest?

a. red

b. green

c. blue-violet

d. yellow

e. orange

c. blue-violet

6. 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?

a. we see them in crowded regions of stars, which give us the impression that the stars there are brighter than they really are

b. all the brightest stars are red, and red color is much easier to see against the black night sky

c. these stars vary in brightness (flashing brighter and dimmer) and are thus easier to notice

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

e. actually, this is just an optical illusion; all stars are really the same brightness

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

7. The most common kinds of stars in the Galaxy have

a. low luminosity compared to the Sun

b. spectra that show they contain mostly carbon

c. enormous masses compared to the Sun

d. diameters thousands of times greater than the Sun's

e. a dozen or more stars in close orbit around them

a. low luminosity compared to the Sun

8. 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)?

a. along the right (vertical axis)

b. along the bottom (the horizontal axis)

c. only in the red giant region

d. only on the main sequence

e. H-R diagrams have nothing to say about spectral types

b. along the bottom (the horizontal axis)

9. Measurements show a certain star has a very high luminosity (100,000 x the

Sun's) while its temperature is quite cool (3500o K). How can this be?

a. it must be a main sequence star

b. it must be quite small in size

c. it must be quite large in size

d. it must be brown dwarf and not a regular star

e. this must be an error in observations; no such star can exist

c. it must be quite large in size

10. Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

a. forming from a reservoir of cosmic material

b. fusing hydrogen into helium in their cores

c. letting go of a huge outer layer

d. dying

e. 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

b. fusing hydrogen into helium in their cores

1. Why did it take astronomers until 1838 to measure the parallax of the stars?

a. because most stars are too faint to see without a good telescope

b. 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

c. because detecting parallax requires measuring a spectrum, which only became possible in the 1830's

d. because cepheid variable stars had not been discovered earlier

e. because no one before then could conceive of the Earth moving around the Sun

b. 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

2. What is the baseline that earth-bound astronomers use to measure the parallax

(the distance) of the nearest stars?

a. the diameter of the Earth

b. the distance between observatories in Greenwich, England and Washington, DC

c. the distance between the Earth and the Moon

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

e. no one can measure parallax for the stars; only for planets in our solar system

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

3. How far away would a star with a parallax of 0.2 arcsec be from us?

a. 2 parsecs

b. 5 parsecs

c. 0.2 parsecs

d. 0.5 parsecs

e. we need more information to answer this question

b. 5 parsecs

4. 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?

a. parallax

b. radar reflections

c. period-luminosity relation for Cepheid variables

d. Kepler's laws

e. there is no way at present to get a distance to an object so far away

c. period-luminosity relation for Cepheid variables

5. 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?

a. its luminosity

b. its radial velocity

c. its temperature

d. its apparent brightness

e. all of these

a. its luminosity

6. 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?

a. there is a star in the system which is not moving at all: it is just sitting there

b. there is a planet orbiting the stars in the system

c. there are huge clouds of dust just behind this star system from our perspective

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

e. there is no explanation of this behavior: it is an unsolved mystery in science

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

7. 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?

a. any gas close to a star will naturally get that hot

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

c. gas gets to be this hot when hydrogen atoms flip their spin and give off 21-cm radiation

d. such gas is heated by the radiation given off by complex molecules in clouds

e. astronomers have no idea how gas gets this hot; this is an unsolved mystery in astronomy

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

8. 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?

a. such molecules are only found in the shadows of the stars

b. such molecules are found only on planets or comets, not in space

c. such molecules are protected by the presence of hot interstellar hydrogen

d. 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

e. such molecules are found only where very cool stars are present, that's why they are so very rare in the Galaxy

d. 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

9. The dust in the dust clouds in interstellar space consists of

a. atomic gas

b. molecular gas

c. tiny solid grains

d. pieces of ice ranging from several meters to a kilometer in diameter

e. none of these

c. tiny solid grains

10. Among interstellar clouds, the hotter the cloud, the

a. the higher the density of particles in it

b. the smaller the diameter of the cloud must be

c. the lower the density of particles in it

d. less likely it is to contain ionized atoms

e. the more likely it is to contain vast quantities of complex molecules

c. the lower the density of particles in it

1. The Orion Nebula is

a. a distant galaxy of stars and raw material

b. a small disk of gas and dust surrounding a single star that was recently formed

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

d. the remnant of a star that exploded several thousand years ago

e. an illusion caused by activity in the Earth's upper atmosphere

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

2. A star whose temperature is increasing but whose luminosity is roughly constant

moves in what direction on the H-R diagram?

a. to the right

b. to the left

c. upwards

d. downwards

e. you can't fool me; stars don't move on the H-R diagram

b. to the left

3. 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?

a. its mass

b. the fraction of its atmosphere that consists of hydrogen

c. whether it is located on the outer regions or the central regions of the molecular cloud that gave it birth

d. the speed and direction of its rotation

e. the size of the disk around it

a. its mass

4. What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?

a. the disks give off x-rays and gamma-rays characteristic of small planets

b. the disks show lanes that are empty of dust within them

c. the disks show evidence of very strong winds coming from the star

d. 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

e. radio telescopes have revealed transmissions from the disks that include rap songs and other evidence of advanced civilizations

b. the disks show lanes that are empty of dust within them

5. What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?

a. block out the light of the star and take a photograph of the fainter planet

b. 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

c. 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

d. search for the presence of metallic and rocky elements in the spectrum of the star

e. look for a small dip in the light of the star when the planet crosses its disk

c. 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

6. The big surprise about the first planet discovered around another regular star was that it

a. was smaller than Mercury or Pluto in our own solar system

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

c. had a mass greater than that of most stars

d. had a spectrum which indicated it was made of elements we never find on Earth

e. was inhabited by intelligent creatures which never had to take astronomy exams

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

7. The telescope that allowed astronomers to discover most of the planets found with the transit method was called

a. the Hubble Space Telescope

b. the Kepler mission

c. the Keck Telescope

d. the Very Large Array of radio telescopes

e. you can't fool me; just about any telescope can show us many, many planet transits

b. the Kepler mission

8. 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)?

a. Such planets always take longer to orbit their stars than the time the mission lasted

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

c. Such planets are only ever detectable using the Doppler shift method

d. Such planets are red in color, and Kepler's cameras could not see red objects

e. Astronomers believe that planets smaller than Mars could not exist

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

9. Planets in the

habitable zone of their stars:

a. are always the planets closest to the star

b. are also called hot Jupiters

c. are so far from their stars that it is very difficult to discover them

d. are at a temperature where water can exist as a liquid

e. cannot exist around stars that are red dwarfs (spectal type M)

d. are at a temperature where water can exist as a liquid

10. 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?

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

b. it would be significantly further away from Proxima Centauri than our is to the Sun

c. it would be in the same position as our habitable zone, but be much wider

d. it would be in the same position as our habitable zone, but be much thinner

e. this question can't be answered until we send a probe to Proxima Centauri

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

1. Which of the following types of stars will spend the longest time (the greatest

number of years) on the main sequence?

a. O

b. A

c. G

d. K

e. every star spends about the same number of years on the main sequence

d. K

2. The event in the life of a star that begins its expansion into a giant is

a. the core reaches a temperature of ten million degrees

b. as much as 90% of the star explodes violently

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

d. the star's internal structure reaches equilibrium for the first time in its life

e. it reaches the stage that astronomers call the zero-age main sequence

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

3. 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?

a. as the star expands, all the layers heat up

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

c. the heat comes from the fusion of carbon in the core, which starts right away

d. the heat comes from the outer layers of the star, which are much hotter than the core

e. this is an unsolved problem in astronomy, but something must be heating that

layer, since we observe red giants out there

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

4. A type of star cluster that contains mostly very old stars is

a. a globular star cluster

b. a stellar association

c. a galaxy

d. an HII region

e. an open cluster

a. a globular star cluster

5. How are globular clusters distributed in our Milky Way Galaxy?

a. completely randomly: you never know where we will find one

b. only in the main spiral disk of the galaxy

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

d. only in the very center of the Galaxy, really crowded together

e. where the giant molecular clouds are found

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

6. 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?

a. the number of M stars on the main sequence

b. the lowest luminosity star that is visible in the cluster

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

d. how high up on the main sequence M type stars are found

e. the coolest surface temperature for a star that they can measure

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

7. Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?

a. because there are no elements heavier than those two; they are the heaviest nuclei in nature

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

c. because all such stars explode before they can make any other elements

d. because all such elements become radioactive and their nuclei break apart rather quickly

e. because the cores of such stars get too hot for further types of fusion to be able to happen

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

8. Really massive stars differ from stars with masses like the Sun in that they

a. go through all the stages of their lives more slowly

b. do not really go through a main sequence stage in their lives

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

d. are no longer forming in the Galaxy; they only formed very early in the Galaxy's history

e. they are significantly less luminous after the main sequence stage is over

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

9. If stars with masses like our Sun's cannot make elements heavier than oxygen,

where are heavier elements like silicon produced in the universe?

a. these heavier elements were made in the Big Bang at the time the universe began, and have been part of the universe ever since

b. heavier elements are made in the proto-planetary disks that accompany many newly forming stars

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

d. heavier elements are made in the cores of planets that are molten and hot when they form

e. this is an unsolved problem in astronomy; no one knows

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

10. 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?

a. the first generation stars never become red giants

b. the first generation stars all live their lives much more slowly than stars today

(so they last a long time)

c. the first generation stars cannot form planets of any kind

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

e. I disagree; I think first generation stars will be like stars forming today in all

ways

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

1. 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?

a. gamma-rays

b. x-rays

c. ultraviolet

d. infrared

e. very long wavelength radio waves

d. infrared

2. When a single star with a mass equal to the Sun dies, it will become a

a. white dwarf

b. neutron star

c. black hole

d. pulsar

e. burster

a. white dwarf

3. A white dwarf, compared to a main sequence star with the same mass, would always be:

a. redder in color

b. smaller in diameter

c. the same size

d. younger in age

e. more massive

b. smaller in diameter

4. 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. how can their presence so soon in the life of the cluster be explained?

a. the lower the mass of a star, the more quickly it goes through each stage of its life

b. white dwarfs are what is left over after a star explodes and throws off 90% of its mass

c. 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

d. 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

e. astronomers can think of no way to explain this problem; it has them completely baffled

c. 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

5. The most stable (tightly bound) atomic nucleus in the universe is:

a. hydrogen

b. carbon

c. uranium

d. technetium

e. iron

e. iron

6. A neutron star is as dense as

a. water

b. the center of the Earth

c. a white dwarf star

d. the nucleus of an atom

e. our astronomy textbook

d. the nucleus of an atom

7. 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?

a. we have been very unlucky; there have been far fewer explosions than average recently

b. 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

c. 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

d. most supernova explosions produce only high-energy gamma-rays and very little light

e. actually, there have been supernova explosions observed, but there is a government conspiracy to keep ordinary citizens from learning about them

c. 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 Galaxyc. 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

8. Elements heavier than iron can be created during:

a. the big bang

b. the main sequence

c. a supernova explosion

d. the red giant stage in a star's life

e. astronomers don't have any idea of where these elements came from; it's an

unsolved mystery

c. a supernova explosion

9. 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?

a. from the width of the pulsar pulses

b. from the color of the nebula's continuous radiation

c. from the spacing of the pulsar pulses

d. from the H-R diagram

e. from the Doppler shift in the line radiation from the nebula

e. from the Doppler shift in the line radiation from the nebula

10. 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?

a. the star that goes nova collides with several stars in a star cluster

b. 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

c. the star that goes nova has a number of massive planets around it which fall in

d. 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

e. a nova explosion happens each time a neutron star rotates to face us, and that happens every century or so

b. 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

HOW DO ASTRONOMERS ESTIMATE THE DISTANCE TO A STAR THAT IS NOT A CEPHEID VARIABLE AND TOO FAR FOR PARALLAX MEASUREMENTS?

•(a) By measuring its temperature and using the Stefan-Boltzmann law

•(b) By determining its luminosity class from its spectrum

•(c) By observing changes in its apparent size over time

•(d) By comparing its motion relative to nearby stars

•(e) By calculating its age based on chemical composition

•(b) By determining its luminosity class from its spectrum

WHAT DO ASTRONOMERS USE TO MEASURE THE DISTANCE TO A CEPHEID VARIABLE STAR?

•(a) Its spectral type and mass

•(b) Its period of variation, apparent brightness, and the period-luminosity relationship

•(c) Its rotational speed and temperature

*(d) Its age and compositor

•(e) Its position in the H-R diagram

•(b) Its period of variation, apparent brightness, and the period-luminosity relationship

WHY IS KNOWING THE DISTANCE TO A STAR IMPORTANT FOR DETERMINING ITS LUMINOSITY?

•(a) Stars of the same type can have different sizes

•(b) Distance affects the temperature of a star

•(c) Brightness decreases with increasing distance, so luminosity cannot be determined without knowing the distance

•(d) Stars farther away are less massive

•(e) A star's apparent brightness does not change with distance

•(c) Brightness decreases with increasing distance, so luminosity cannot be determined without knowing the distance

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

(A. location where they are born

B. time they are born

C. luminosity they are born with

D. mass they are born with

E. color they are born with

D. mass they are born with

WHAT CAUSES DARK REGIONS IN THE GALAXY THAT OBSCURE THE LIGHT FROM STARS

BEHIND THEM?

•(a) Interstellar dust clouds blocking starlight

•(b) Low-mass stars emitting little light

*(c) Large, nearby planets casting shadows

*(d) Black holes absorbing surrounding light

•(e) Gas clouds reflecting starlight

•(a) Interstellar dust clouds blocking starlight