final exam

Question 1

A star is 230 light-years away. The light we see tonight from that star left it

Answer 1

Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.

Question 2

The point in the sky directly above your head at any given time is called the

Answer 2

zenith

Question 3

The path that the Sun appears to make in the sky over the course of a year is called the celestial equator

Answer 3

FALSE

Question 4

The great astronomer of ancient times who summarized and improved a system of circles upon circles to explain the complicated motions of the planets (and published the system in a book now called The Almagest) was

Answer 4

Ptolemy

Question 5

The scientist who first devised experimental tests to demonstrate the validity of the heliocentric model of the solar system was

Answer 5

Galileo

Question 6

The celestial sphere turns around once each day because

Answer 6

Our position on a rotating Earth causes the stars, planets, and Sun to appear to revolve around us.

Question 7

Which ancient Greek thinker suggested (long before Copernicus) that the Earth is moving around the Sun?

Answer 7

Aristarchus i

Question 8

In this diagram of the celestial sphere, there are five lines that point to different parts of the picture. Use the drag-and-drop environment to label the indicated parts of the figure.

Answer 8

The location of the figure defines which direction the zenith is located: always directly overhead of the observer. This point travels with the observer, in a sense, and the horizon with it since the horizon is 90° from the zenith in all directions.
The North Celestial Pole, on the other hand, is fixed against the background stars based on the direction our planet’s rotational axis points, so its position in one’s local sky may vary as a result of one’s location on the Earth’s surface, and the Celestial Equator with it since the Celestial Equator is 90° from the North Celestial Pole in all directions.

Question 9

At the Earth’s equator, you would see the celestial poles on your horizon.

Answer 9

true

Question 10

How did Eratosthenes measure the size of the Earth?

Answer 10

The memory aid “altitude = latitude” applies to the north celestial pole’s altitude as seen from a particular latitude on Earth, but the idea translates to observing the Sun as well. Although the Sun’s altitude from a particular latitude depends on the time of year, the difference between the observed altitude of the Sun from two latitudes at local solar noon, tells you the difference in latitude between those two locations.
Eratosthenes took advantage of this idea by comparing the altitude of the Sun h1
at noon as seen from his town (measured by observing the shadow cast by a pillar or post in the ground) with the altitude of the Sun h2
at noon as seen from a different town to the south. He recognized that the difference between the two observed altitudes compared to the full 360 degrees in a circle is equal to the distance between the two towns d
compared to the full circumference of the Earth C
:
h1−h2/360∘=dC
From this expression he was able to calculate the circumference of the Earth in the same physical units as the distance between the two towns.

Question 11

In an ellipse, the ratio of the distance between the foci and the length of the major axis is called

Answer 11

eccentricity

Question 12

remember newtons laws

Answer 12

ok

Question 13

Consider an ellipse with a major axis of l = 6 cm and an eccentricity of e = 0.71.

Answer 13

Part (a) What is the length of the semimajor axis a
, in cm?
The semimajor axis a
of an ellipse is half the major axis; the eccentricity plays no role in this calculation.
a=l/2 =6 cm / 2
a=3.000 cm

Question 14

Kepler’s third law relates a planet’s orbital period to the semi-major axis of the orbit.

Answer 14

TRUE

Question 15

The diagram below shows the seasons that our planet Earth undergoes for the Northern Hemisphere. The position of the Earth is labeled for one of the key seasonal dates, the Autumnal (Fall) Equinox. Label the other three positions correctly. Note the blue arrow on the circle of the Earth’s orbit, which shows which way the Earth moves.

Answer 15

just google it

Question 16

Which of the following statements about electromagnetic radiation is FALSE?

Answer 16

Not only are photons (the particles of light) massless, but they are also electrically neutral.

Question 17

Which, from among the following options, has the longest wavelength?

Answer 17

The lowest-energy forms of light have the longest wavelengths. These forms of light include infrared waves, microwaves, and (at the absolute longest) radio waves.

Question 18

A star has a surface temperature of 8800 K. At what wavelength (in nanometers) will it give off maximum light?

Answer 18

This form is useful when we are given a temperature in kelvins (K) or a wavelength in nanometers (nm). Since this is the case, we can solve for the temperature with a little algebra and plugging in the given value of the temperature:
λmax=2.9×10^6 nm⋅K/T
= 2.9×10^6 nm⋅K/ 8800 K
T=329.5 nm

Question 19

Fill-in-the-blank

Answer 19

Understanding Blackbody Radiation: It turns out that stars behave like an idealized object that scientists call a blackbody. Thus, understanding blackbodies and how they give off energy helps us to understand how stars shine. For a blackbody, the higher its temperature, the smaller the wavelength at which it gives off the peak amount of radiation. This is described by wien’s law. Thus, really hot stars will shine most intensely with ultraviolet radiation. Also, the higher a star’s temperature, the greater the flux of radiation coming from it. This last statement is called stefan-Boltzman law.

Question 20

For all electromagnetic waves, the frequency multiplied by the wavelength will be the same constant number.

Answer 20

True

Question 21

fill in the blank

Answer 21

When someone who has never thought much about astronomy looks up at the sky, it’s easy to believe that everything turns around the Earth and that we are in the middle of things; such a view is called the geocentric model. Astronomers call the point in the sky above our heads our Zenith, and where the dome of the sky meets the Earth our Horizon. In the 20th century, astronomers divided the sky into 88 boxes, and each box is now called a Constellation. The belt of the sky through which the Sun, Moon, and planets are seen to move in the course of the day and the course of a year is called the Zodiac.

Question 22

fill in the blank

Answer 22

If you were standing at Earth’s north pole, and you looked up to the zenith (the point directly above your head), you would be looking at the point where the North Celestial pole is located. At the Earth’s North Pole, the celestial equator would be at your Horizon . If, on the other hand, you were at the Earth’s equator, you would see one point of the celestial equator pass through your Zenith If you are looking at the sky from the continental United States, the north celestial pole would have an angular height (an altitude) equal to your Latitude. Right now, the star located very close to our north celestial pole is Polaris.

Question 23

A light-year is

Answer 23

Equal to approximately 9.5 trillion km, or 5.9 trillion miles, the distance that light travels in one Earth year is a commonly-used unit of length or distance in astronomy.

Question 24

A star is 230 light-years away. The light we see tonight from that star left it

Answer 24

Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.

Question 25

The Astronomical Unit (AU) as defined by astronomers is

Answer 25

Astronomers defined this as a distance unit because the actual distance in any physical unit in use at the time was not known.

Question 26

If a star is 900 light-years away, that means the light we see tonight left that star 900 years ago.

Answer 26

TRUE

Question 27

By looking billions of light-years out into space, astronomers are actually seeing billions of years into the past.

Answer 27

TRUE

Question 28

At the Earth’s equator, you would see the celestial poles on your horizon.

Answer 28

true

Question 29

The Sun revolves around (orbits) the Earth in about 365 days (what we call one year.)

Answer 29

FALSE

Question 30

We now know that the orbit of a stable planet around a star like the Sun is always in the shape of

Answer 30

ellipses.

Question 31

When a planet, in its orbit, is closer to the Sun, it

Answer 31

moves faster (perihelion)

Question 32

According to Kepler's third law, there is a relationship between the time a planet takes to revolve around the Sun and the planet's

Answer 32

Kepler's 3rd law is written as an equation: p^2=a^3 In this equation, p corresponds to the orbital period, the time a planet takes to revolve around the Sun. The quantity a corresponds to the average orbital distance from the Sun (the semimajor axis). In words, this means that planets which orbit farther from the Sun on average have longer orbital periods.

Question 33

Newton showed that to change the direction in which an object is moving, one needs to apply

Answer 33

Newton's 2nd law of motion describes the means by which the motion of an object can be changed through the action of an outside force. Such a force, when applied to an object, produces an acceleration in that object that is inversely related to its mass (more-massive objects accelerate less under a given force than less-massive objects). Quantitatively, this takes on the equation form F=ma This acceleration can be a simple change in speed, a change in the direction of motion, or both.

Question 34

Which of the following statements about the force of gravity is FALSE?

Answer 34

The force of gravity between two masses M and m whose centers are separated by some distance d takes on the mathematical form FG=GMm/d^2 By this description, increasing either term in the numerator (M or m ) increases the gravitational force between the two objects. Increasing the denominator, on the other hand, decreases the strength of the force.

Question 35

The figure to the right shows a set of ellipses. The ellipse on the top has a semimajor axis of 1 (in some arbitrary unit). The four choices below it in the grey region have their sizes shown (in the same arbitrary units). Based on the given semi-major axis for the orbit in the white region above, which of the lettered orbits would have the same orbital period?

Answer 35

Kepler's 3rd law is stated most simply that there is a direct relationship between the orbital period p of an object and the orbit's semimajor axis a : p^2=a^3 The semimajor axis is half of the full length of the major axis, which means in this case that the orbit in question has a major axis of 2 units. An orbit that will have the same period, then, will also have a major axis of 2 units. Among the four choices shown, this corresponds to orbit d.

Question 36

The number of degrees of arc that your location is north or south of the Earth's equator is called your

Answer 36

Lines of latitude run east-west in parallel circles around the Earth, measuring an angle north or south from the Earth's equator.

Question 37

The "prime meridian" (where longitude equals zero) passes through

Answer 37

This city is the site of the Royal Observatory, in Greenwich, England.

Question 38

To locate objects on Earth, we call the number of degrees east or west of the Greenwich Meridian its:

Answer 38

longitude

Question 39

A solar day is slightly longer than a sidereal day.

Answer 39

true

Question 40

How fast do electromagnetic waves travel?

Answer 40

Electromagnetic waves are the formal term for what we call "light" - which travels at the speed of light regardless of its energy.

Question 41

The fastest speed in the universe is

Answer 41

Einstein's theory of relativity says it the speed of light

Question 42

Wien's law relates the wavelength at which a star gives off the greatest amount of energy to the star's

Answer 42

Wien's law describes the relationship between the temperature of an object like a star and the wavelength at which it gives off the greatest amount of energy: λmaxT=2.9×10^6 nm K

Question 43

The Stefan-Boltzmann law relates the energy flux coming from a blackbody (such as a star) to its

Answer 43

The Stefan-Boltzmann law describes the relationship between the star's temperature and its energy flux F (power emitted per unit area): F=P/A=σT^4

Question 44

The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is stationary with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths. Suppose instead that the source was actually moving away from you at a high speed. Which of the (smaller) lettered spectra would you expect the observed spectrum to resemble? (In this scenario, the large spectrum at the top is the emitted spectrum.)

Answer 44

The large spectrum that is shown is what is being emitted by the source. It would be the spectrum you would observe if there was no motion occurring. However, the scenario describes motion away from you, and such recessional motion introduces a redshift. The red end of the spectrum is the one where wavelengths are longer, so the spectrum you will observe is the one where the absorption lines have been shifted to the longer wavelength end - in this case, to the right.

Question 45

The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is stationary with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths. Suppose instead that the source was actually moving away from you at a high speed. Which of the (smaller) lettered spectra would you expect the observed spectrum to resemble? (In this scenario, the large spectrum at the top is the emitted spectrum.)

Answer 45

The large spectrum that is shown is what is being emitted by the source. It would be the spectrum you would observe if there was no motion occurring. However, the scenario describes motion toward you, and such approaching motion introduces a blueshift. The blue end of the spectrum is the one where wavelengths are shorter, so the spectrum you will observe is the one where the absorption lines have been shifted to the shorter wavelength end - in this case, to the left.

Question 46

The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is moving with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths. Part (a) Suppose you were told that the source was moving toward you at a high speed. Which of the spectra below would you expect the actual emitted (rest-frame) spectrum to resemble? (In this scenario, the large spectrum at the top is the observed spectrum.)

Answer 46

The large spectrum that is shown is what is being observed from the source, and you know that motion is happening so you know it has been Doppler-shifted one way or the other. The scenario describes motion toward you, and such approaching motion introduces a blueshift. The blue end of the spectrum is the one where wavelengths are shorter, so the spectrum you are observing is one where the absorption lines have been shifted toward the shorter wavelength end - in this case, to the left. This means the original emitted spectrum was toward the right.

Question 47

Not all wavelengths of electromagnetic radiation can penetrate the Earth's atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet's surface?

Answer 47

Although our atmosphere is very effective at absorbing most forms of light, visible light and most radio wave light can penetrate to the surface - which is why radio telescopes do not need to be launched into space.

Question 48

A carrier wave on a campus radio is broadcasting at a frequency f = 87.5 MHz. What is the wavelength λ of the carrier wave of this radio, in meters?

Answer 48

The relationship between a light wave's speed c , its wavelength λ , and its frequency f , is given by λf=c so the wavelength can be found by using some algebra and plugging in the given values λ=c/f. = (3×10^8 m/s)/87.5×10^6 Hz

Question 49

The emitted infrared radiation from a dwarf planet has a wavelength of maximum intensity at λmax = 72000 nm. What is the temperature T , in kelvins, assuming it follows Wien's law?

Answer 49

Wien's law describes the relationship between the temperature T of an emitting body and the peak wavelength λmax of its spectrum λmaxT=2.9×10^6 nm⋅K This form is useful when we are given a temperature in kelvins (K) or a wavelength in nanometers (nm). Since this is the case, we can solve for the temperature with a little algebra and plugging in the given value of the peak wavelength: T=2.9×10^6 nm⋅K/λmax =2.9×10^6 nm⋅K/ 72000 nm T=40.28 K

Question 50

To break up light into the component colors that it contains, astronomers use a device called

Answer 50

This device can use either a prism or a diffraction grating to reveal the spectrum, and goes by many names: spectrometer, spectrograph, or spectroscope.

Question 51

What type of telescope can be used routinely on the surface of the Earth during the DAY? Part (a) Please select the best choice from the available options.

Answer 51

a radio telescope 

Question 52

The most important function of an astronomical telescope is to

Answer 52

Telescopes function by making dim objects brighter and small features more easily resolved. In order to perform both functions, they must collect light and bring it to a focus.

Question 53

Which of the following types of star is the coolest (has the lowest surface temperature)? Part (a) Please select the best choice from the available options.

Answer 53

M

Question 54

A star has a parallax of 0.11 arcsec. Part (a) What is the star's distance in parsecs?

Answer 54

Distance = 1/p Distance = 1/0.11 Distance = 9.091 Tolerance: ± 0.27

Question 55

Two stars have a magnitude difference of 0.75. Part (a) How many times greater is the apparent brightness of the brighter star?

Answer 55

Number of times brighter = 100^(0.2*mag) Number of times brighter = 100^(0.2*0.75) Number of times brighter = 1.995 Tolerance: ± 0.060

Question 56

The amount by which the spectral lines of a star is redshifted tells astronomers how fast the star is moving away from us.

Answer 56

TRUE

Question 57

Star A and Star B are located at different distances but have identical apparent brightnesses. Part (a) If Star A is located 3 times farther away than Star B, how many times more luminous is Star A than Star B?

Answer 57

Factor = d^2 Factor = 3^2 Factor = 9.000 Tolerance: ± 0.27

Question 58

Astronomers use the term interstellar matter to refer to:

Answer 58

gas and dust that lies between stars 

Question 59

Labeling This diagram shows different kinds of light spectra. Please insert the correct labels for each part of the figure.

Answer 59

just look it up

Question 60

Labeling Shown here is the Orion Nebula. The photo shown here illustrates all three types of nebulae associated with regions where stars form.

Answer 60

look it up

Question 61

An HII region is

Answer 61

a zone around a hot star where hydrogen atoms are ionized 

Question 62

The red color we see on a lot of photographs of nebulae comes from which element?

Answer 62

hydrogen 

Question 63

Why do all stars spend most of their lives on the main sequence?

Answer 63

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 

Question 64

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

Answer 64

a globular star cluster 

Question 65

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

Answer 65

because such a star just cannot get hot enough for the fusion of heavier nuclei 

Question 66

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

Answer 66

white dwarf 

Question 67

If you want to find stars that are just being born, where are the best places to search?

Answer 67

in giant molecular clouds 

Question 68

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?

Answer 68

to the left

Question 69

Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?

Answer 69

when nuclear fusion reactions begin inside its core 

Question 70

Labeling On the H-R diagram shown, drag to each position the correct name or term in the early evolution of a 1 MSun star. Part (a) Please use the drag-and-drop environment to label the missing parts of the figure.

Answer 70

look it up

Question 71

Which of the following statements about the main sequence stage in the life of a star is FALSE?

Answer 71

main sequence stars are rare in the Galaxy, so we are lucky to be living around one 

Question 72

How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on

Answer 72

its mass 

Question 73

As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?

Answer 73

from the fusion of hydrogen into helium in a shell around the core 

Question 74

The Life Stages of a Star Note: Some words are missing from the following paragraph.

Answer 74

Like people, stars go through various distinct stages in their lives. For 90% of its life, each star is in the ______main sequence _______________________ stage, when it fuses hydrogen into helium and stays relatively stable. After the hydrogen hot enough for fusion is exhausted, the star's core begins to collapse under its own weight, and fusion begins in a ______shell of hydrogen_______________________ outside the core. All the energy from this fusion pours outward and causes the outer layers of the star to _______expand ______________________. If the star is relatively low mass, the result (as seen from the outside) is a ___red giant__________________________ star. When this happens to the Sun, the new star will swallow the planet ______venus_______________________. Eventually, the collapsing core of the star will get hot enough for the next step in nuclear fusion, which astronomers call the _____triple alpha process________________________.

Question 75

The Lives of Stars After the Red Giant Stage Note: Some words are missing from the following paragraph

Answer 75

After the main sequence stage of a star’s life is over, the star undergoes some periods of instability. The swelling up of a star to become a red giant or red supergiant ends when the next step in fusion begins with the fusion of helium into the element __carbon_____. In low-mass stars, the entire core is ignited quickly in an event called the ___helium flash ________. In some stars, when the temperature is hot enough, another atom of helium can be added, to make the next element that is a product of fusion by helium, the element ____oxygen________. For low mass stars, the core temperature cannot rise further to make additional elements, and the star must soon die. The core (and the star along with it) now shrinks and heats up, and ejects a shell of material which begins to glow (energized by the ultraviolet light of the hot star). These glowing shells were given the misleading name of a ___planetary nebula___________. More massive stars, on the other hand, can continue to get their cores hotter, and to fuse even heavier elements, such as ____silicon__________ (which is common on Earth).

Question 76

Ranking Put the following in order of total Luminosity, from the least luminous to the most luminous:

Answer 76

look at exam 2 solutions

Question 77

Identify The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E. Part (a) Click the letter label that corresponds to the point in a star’s evolution where it is fusing hydrogen to helium in its core.

Answer 77

look at exam 2 solution

Question 78

Identify The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E. Part (a) Click the letter label that corresponds to the point in a star’s evolution where it will spend the most time.

Answer 78

ex 2

Question 79

Identify The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E. Part (a) Click the letter label that corresponds to the point in a star’s evolution where it is fusing hydrogen to helium in a shell around in an inert helium core.

Answer 79

ex 2

Question 80

A star has a parallax of 0.11 arcsec. What is the star's distance in parsecs?

Answer 80

What is the star's distance in parsecs? Distance = 1/p Distance = 1/0.11 Distance = 9.091 Tolerance: ± 0.27

Question 81

A particular star is 11 parsecs away from Earth. What will this star's observed parallax be as seen from Earth? Express your answer in arcseconds.

Answer 81

p = 1/d p = 1/11 p = 0.09091 Tolerance: ± 0.0027

Question 82

A particular star has an apparent magnitude of +10.5 and an absolute magnitude of +2 .

Answer 82

Part (a) Calculate the star's distance, in parsecs. Distance = 10^((N1-N2+5)/5) Distance = 10^((10.5-2+5)/5) Distance = 501.2 Tolerance: ± 15 Part (b) Calculate the parallax such a star would exhibit. Parallax = 1/10^((N1-N2+5)/5) Parallax = 1/10^((10.5-2+5)/5) Parallax = 0.001995 Tolerance: ± 6.0×10−5

Question 83

A type of star that has turned out to be extremely useful for measuring distances is

Answer 83

the Cepheid variables 

Question 84

A light curve for a star measures how its brightness changes with

Answer 84

time

Question 85

The higher the luminosity (intrinsic brightness) a Cepheid variable is,

Answer 85

the longer the period of its variations 

Question 86

One problem with Cepheid variable stars is that their period changes from year to year.

Answer 86

FALSE

Question 87

All known Cepheid variable stars take less than 6 hours to go through one cycle of variations.

Answer 87

FALSE

Question 88

For Cepheid variables, the longer the period, the greater the luminosity.

Answer 88

true

Question 89

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?

Answer 89

its mass 

Question 90

Which of the following stages will the Sun definitely go through as it gets older?

Answer 90

all these 

Question 91

When the mass of a star's core is greater than 1.4 times the mass of the Sun, degenerate electrons can't keep it stable as a white dwarf. Instead, it becomes:

Answer 91

a neutron star 

Question 92

Which of the following stages can only occur in the life of a low-mass star (whose final mass is less than 1.4 times the mass of the Sun)?

Answer 92

white dwarf

Question 93

Ranking The images shown illustrate several steps in the evolutionary cycle of a low-mass star. Arrange them in correct chronological order, from formation to death.

Answer 93

protostar< main sequence < red giant < planetary nebula< white dwarf

Question 94

Ranking The images shown illustrate several steps in the evolutionary cycle of a high-mass star. Arrange them in correct chronological order, from formation to death. Part (a) Please use the drag-and-drop environment to label the missing parts of the figure from formation to death.

Answer 94

protostar< main sequence< red giant < supernova < neutron star

Question 95

The maximum mass that a star can end its life with and still become a white dwarf is about 1.4 times the mass of our Sun.

Answer 95

true

Question 96

A black dwarf is a white dwarf that has cooled down so much it gives off very little visible light anymore.

Answer 96

true

Question 97

An H-R Diagram plots the luminosity of stars against their:

Answer 97

surface temperature

Question 98

n 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)?

Answer 98

along the bottom (the horizontal axis) 

Question 99

Measurements show a certain star has a very high luminosity (100,000 times the Sun's) while its temperature is quite cool (3500 K). How can this be?

Answer 99

it must be quite large in size  

Question 100

question 15 on exam 2

Answer 100

HR diagrams

Question 101

Imagine studying two stars which have identical luminosities but different spectral types. Which statement below will also be true about these two stars?

Answer 101

They have identical absolute magnitudes.

Question 102

Imagine studying two stars which have identical spectral types but different luminosities. Part (a) Which statement below will also be true about these two stars?

Answer 102

They have identical temperatures.

Question 103

Imagine studying two main sequence stars which have different spectral types, but for which nothing else has been determined. Part (a) Which statement below will also be true about these two stars?

Answer 103

They could have some similar spectral lines.

Question 104

The amount of time a star spends on the main sequence depends on its mass, as shown in this table of main sequence lifetimes. Part (a) How many times longer does a 1.1 -solar-mass star stay on the main sequence compared to a 3.3 -solar-mass star?

Answer 104

Factor = (9 * 10^9)/(500 * 10^6) Factor = 18.00 Tolerance: ± 0.54

Question 105

An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?

Answer 105

a radio telescope, tuned to a wavelength of about 21 centimeters 

Question 106

An HII region (emission nebula) is

Answer 106

a zone around a hot star where hydrogen atoms are ionized 

Question 107

17 and 19 on exam 2

Answer 107

look over that

Question 108

Our Milky Way Galaxy is what type of galaxy?

Answer 108

spiral

Question 109

The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:

Answer 109

elliptical

Question 110

Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?

Answer 110

their shape

Question 111

After several decades of observation, astronomers have concluded that quasars are

Answer 111

very powerful and compact sources of energy at the centers of distant galaxies 

Question 112

Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is

Answer 112

matter falling toward a supermassive black hole at the center of a galaxy 

Question 113

Which of the following objects is considered useful to astronomers as a "standard candle" for determining distances?

Answer 113

white dwarf (type Ia) supernovae 

Question 114

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the

Answer 114

the faster it is moving away from us 

Question 115

Suppose we measured the distance to a galaxy and it turned out to be 180 million light-years away. The galaxy's redshift tells us its recessional velocity is 5,000 km/s. If the Hubble constant was determined merely from measurements of this galaxy alone, what would we find it to be in km/s per million light-years?

Answer 115

Constant = 5000/d Constant = 5000/180 Constant = 27.78 Tolerance: ± 0.83

Question 116

A line in the absorption spectrum of hydrogen from a quasar has a wavelength of 543 nm. At rest (in an Earth laboratory, for example) that same line has a wavelength of 486 nm. What is the redshift, z of this quasar?

Answer 116

z = (n-486)/486 z = (543-486)/486 z = 0.1173 Tolerance: ± 0.0035

Question 117

A quasar is moving away from us at v/c=0.8 What will the redshift of this quasar be measured as?

Answer 117

Redshift = sqrt((1+0.8)/(1-0.8))-1 Redshift = 2.000 Tolerance: ± 0.060

Question 118

The reciprocal of the Hubble constant (1/H) is a rough measure of the:

Answer 118

the age of the universe 

Question 119

If the expansion of the universe were accelerating, it would mean that distant Type Ia supernovae would look fainter than we would expect from measuring their redshifts and applying Hubble’s law.

Answer 119

true

Question 120

As the universe expands, the temperature throughout the universe increases regularly.

Answer 120

false

Question 121

The figure here shows an exaggerated version of the modern Hubble diagram revealed by the Hubble Space Telescope. The blue dashed boxes correspond to two regions on this diagram we will compare.

Answer 121

top right

Question 122

All the evidence currently suggests that we live in closed universe.

Answer 122

false

Question 123

The latest conclusion that astronomers have reached about the expansion of the universe is that the rate at which space is expanding is decelerating – that is, the expansion is slowing down due to the pull of gravity.

Answer 123

false

Question 124

Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?

Answer 124

the measurement of galaxy distances using white dwarf (type Ia) supernovae 

Question 125

The cosmic microwave background is

Answer 125

microwave radiation coming from all directions that is the redshifted afterglow of the Big Bang.

Question 126

The cosmic microwave background has a temperature of 2.725 K . Calculate its peak wavelength, in millimeters.

Answer 126

Wavelength = 2898/2.725/1000 Wavelength = 1.063 Tolerance: ± 0.032

Question 127

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?

Answer 127

95 percent