Astronomy Exam 4
A star is found to have absolute magnitude -1 and apparent magnitude 19. How far away is it?
100,000 parsecs.
Spectroscopic Parallax refers to
a method for finding distances to stars.
A steady X-ray signal with sudden bursts lasting a few seconds each is probably caused by
a neutron star in a binary system.
Which of the following objects is closest in size to a black hole formed from the collapse of a star?
a neutron star.
29 A star whose full spectral type is K2V is
a red main sequence star.
A star whose full spectral type is K2V is
a red main sequence star.
A mirror that is supposed to bring light from a star directly overhead to a focus must be shaped like
a shallow bowl with the open part facing up.
Type II supernovas have the following properties:
a spectrum with hydrogen lines and a variable maximum brightness.
The problem of stars "twinkling" due to atmospheric turbulence
can be corrected by using a guide star.
The property of electron-degenerate matter that is important in the evolution of a star is that this type of matter
cannot be compressed and heated.
The intense magnetic field of the Crab pulsar causes its rate of spin to
decrease.
For stars on the main-sequence, stars with decreasing mass have
decreasing surface temperature and absolute brightness
For stars on the main-sequence, stars with decreasing mass have
decreasing surface temperature and absolute brightness.
A red subgiant star is one that has a
decreasing surface temperature and nearly constant brightness.
Nuclei such as protons do not fuse at low temperatures because their speeds are not enough to overcome their
electrical repulsion.
Which of the following particles has the smallest mass?
electron.
The point at which even an outwardly directed light ray is pulled into a black hole is called the
event horizon.
Supernova explosions tend to
form elements heavier than iron.
The X-rays that reveal the possible presence of a black hole are the result of
matter heating up as it falls toward the hole.
When the temperature of a gas decreases, its molecules
move slower.
When the helium fuel runs out at the center of a low-mass star like our Sun,
moves off of the horizontal branch.
A star with an absolute magnitude of 8.4 and an apparent magnitude of -1.0 would appear in our sky as a star
of dazzling brightness.
One conclusion that was drawn from the gradual slowing of the radio signals from the Crab Nebula was that they were probably
of natural origin.
On a Hertsprung-Russel diagram, stars that are burning Helium at their cores are found
on the Horizontal Branch.
The wavelength of the sound waves that correspond to middle-C is about 4 feet. If you are standing 4 feet away from a piano that is playing that note, then between you and the piano there will usually be
one region of maximum pressure.
For a spectroscopic binary star system, we can determine
only a minimum mass for each star.
Which of the following particles would be repelled by a proton?
positron.
A hydrogen atom with its electron removed (a H⁺ ion in other words) is actually a
proton.
Neutron stars are often observed as
pulsars.
A star that is cooler than most other stars will probably look
red.
To see small but bright objects such as the ice caps on Mars, you would need a telescope with large
resolving power.
38 A star that is 10,000 miles in diameter is probably a
white dwarf star.
45 A star that is approximately the size of the Earth is probably a
white dwarf star.
A star that is 10,000 miles in diameter is probably a
white dwarf star.
A star that is in the lower left corner of an HR diagram is most likely a
white dwarf star.
The lower left of a Hertzsprung-Russell diagram is where one finds
white dwarf stars.
Compared to a magnitude 6 star, a magnitude 1 star would be
100 times as bright.
36 Which of the following spectral types corresponds to a star on the main sequence?
(G2V)
2 Nuclear fusion requires high temperatures because nuclei
(repel each other.)
50 Nuclear fusion requires high temperatures because nuclei
(repel each other.)
46 A black hole that has formed from the collapse of a star is expected to be
(similar in size to a neutron star.)
30 A spectroscopic binary star system is one in which we see
(spectral lines shifting back and forth.)
24 Epsilon Eridani shows a proper motion of 0.97661 arc seconds per year. In 100 years, its position in the sky changes by
(97.661 seconds of arc.)
37 In the Hertzsprung-Russelll Diagram shown, which point represents a star of type F with absolute magnitude -5?
(C)
26 Once a star has evolved onto the Main Sequence in the HR Diagram, it
(stays at the same point until it runs out of fuel.)
13 Of all the things that might go wrong with distances found by using the method that astronmers refer to as the "distance ladder," which of these is the one that an astronomer would say is most likely?
(Distant objects are not behaving the same as nearby objects.)
39 Think of the ëfrontíof a telescope as the end that light enters. A telescope with Newtonian Focus has the eyepiece
(sticking out the side near the front.)
6 Think of the front of a telescope as the end that light enters. A telescope with Newtonian Focus has the eyepiece
(sticking out the side near the front.)
43 Which of these answers describes the fundamental assumption that is behind all of the methods that astronomers refer to as the "distance ladder?"
(Distant objects are similar to nearby objects.)
38 The mass of a carbon atom is 12.00amu while the mass of a helium-4 atom is 4.003amu. If a gamma ray photon splits a carbon atom into three Helium atoms, how much energy is converted into mass?
(0.009amu)
9 The mass of a carbon atom is 12.00amu while the mass of a helium-4 atom is 4.003amu. If three atoms of helium fuse to form carbon, how much mass is converted into energy?
(0.009amu)
11 Which of the following magnitudes corresponds to the brightest star?
(0:)
41 A star is seen to move by 0:4 seconds of arc between March 1, 1999 and September 1, 1999 and then back to its starting point on March 1, 2000. What is the parallax angle for this star?
(0:2 seconds of arc.)
50 A star is seen to move by 0.8 seconds of arc between March 1, 1999 and September 1, 1999 and then back to its starting point on March 1, 2000. What is the parallax angle for this star?
(0:4 seconds of arc.)
23 Barnardís star is a near neighbor of the Sun whose properties we know quite well. It is a type M4V with absolute magnitude 13.22. Suppose that another star of spectral type M4V is observed to have apparent magnitude 8.22. How far away is it?
(1 parsec.)
9 Cruising far from the Sun, we notice that the Sunís apparent brightness has dimmed to 10 watts per square meter. We know that the apparent brightness at a distance of 1au is 1000 watts per square meter. How far from the Sun are we?
(10 au
27 A starship observes that a nearby star has apparent magnitude 4.0. The spectrum of the star indicates that it is a type that normally has absolute magnitude 4.0. From these observations, the starship knows that it is
(10 parsecs from the star.)
4 Cruising far from the Sun, we notice that the Sunís apparent brightness has dimmed to 0:1 watts per square meter. We know that the apparent brightness at a distance of 1au is 1000 watts per square meter. How far from the Sun are we?
(100 au)
14 Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude 4:8. If the starís apparent magnitude is found to be 14:8, how far away is it?
(1000 parsecs.)
35 A star at a distance of 100pc should have an apparent brightness equal to its absolute brightness multiplied by
(10^-2)
25 Suppose that a sound wave has a wavelength of 12 meters and a frequency of 100Hz. What is the speed of sound?
(1200 m/s)
18 Suppose that a áash of lightning from a cloud 2500 meters away is followed by a clap of thunder two seconds later. Assume that the light arrived in a negligible time and calculate the speed of the sound waves.
(1250m/s)
15 Compared to a magnitude 16 star, a magnitude 1 star would be
(1; 000; 000 times as bright.)
43 You hear a 1000Hz tone from a radio that is 20 feet away from you and listen for 5 seconds. How many pressure maxima pass by your ear?
(5000)
19 Suppose that you want to double all of the dimensions of a telescope that uses a large lens to collect light. The amount of glass that you need to form the lens of the new, twice as large, telescope is
(8 times the amount needed for the original telescope.)
1 The star Wemadeit shows a stellar parallax angle of 0.2 seconds of arc while the star Waytoofar shows a stellar parallax angle of 0.3 seconds of arc. From this, you can conclude that
(Waytoofar is closer to our Sun than Wemadeit.)
22 The star Wemadeit shows a stellar parallax angle of 0.3 seconds of arc while the star Waytoofar shows a stellar parallax angle of 0.2 seconds of arc. From this, you can conclude that
(Wemadeit is closer to our Sun than Waytoofar.)
40 The object Gliese 229B glows in the infrared but is much cooler and dimmer than a class M star and shows traces of lithium that a normal star would quickly burn up in the nuclear reaction that occurs in its core. This object is most likely
(a brown dwarf.)
34 The word Parallax in the term Spectroscopic Parallax is used because that term refers to
(a method for Önding distances to stars.)
47 The idea that a supernova is preceded by a huge burst of neutrinos is
(a prediction that has now been observed.)
48 A pulsar is really
(a spinning neutron star.)
16 A type Ia supernova occurs when
(a white-dwarf begins to collapse.)
37 The First red giant stage of a one solar mass star's life usually ends
(an explosion in the helium core.)
47 The first red giant stage of a one solar mass star's life usually ends with
(an explosion in the helium core.)
In a Hertzsprung-Russell diagram, the brightest stars are found
(at the top.)
39 Adaptive optics is used to correct telescopes for
(atmospheric turbulence.)
42 A star that forms an iron core most likely has a mass of
(between 15 and 20 solar masses.)
21 Stellar Parallax
(can only be seen with a telescope.)
4 Ham radio operators sometimes operate receivers for the 2 meter wavelength. The 2 meters refers to the
(distance from one maximum of the radio waves to the next
11 The red subgiant stage of a star is best described by
(dropping temperature and constant brightness.
10 The core of a red supergiant star stops shrinking because its
(electrons touch each other.)
49 The point at which even an outwardly directed light ray is pulled into a black hole is called the
(event horizon.)
44 Stars that are much more massive than our Sun
(form faster and burn out faster.)
45 Stars that are much less massive than our Sun
(form more slowly and burn slower.)
42 The origin of the energy that is released in a supernova explosion is
(gravitational energy from the core collapse.)
A main-sequence star with more mass than our sun will be
(hotter and brighter.)
17 In the Hertzsprung-Russell Diagram, a main sequence star would not be found
(in the upper right or lower left.)
3 Stars with more than 15 times the mass of our Sun usually evolve off the main sequence along a path in the HR diagram that
(is mostly horizontal.)
12 When the temperature of a gas increases, its molecules
(move faster.)
32 Suppose that a star has a spectrum that includes red, blue, and violet lines spaced in the pattern of the lines from hydrogen but the violet lines are at 444nm and 420nm instead of the usual 434nm and 410nm. From this evidence, you can conclude that the star is
(moving away from us.)
10 When a white dwarf star collects matter from a neighboring star, fusion reactions on the surface of the white dwarf cause
(novas
8 When a white dwarf star collects matter from a neighboring star, fusion reactions on the surface of the white dwarf cause
(novas.)
5 A star with an absolute magnitude of 8:4 and an apparent magnitude of 1:0 would appear in our sky as a sta
(of dazzling brightness.)
20 On a Hertsprung-Russel diagram, stars that are burning Helium at their cores are found
(on the Horizontal Branch.)
7 A converging lens will send the light from a distant star through a point
(on the focal plane of the lens.)
41 The formation of a new white dwarf is usually accompanied by a
(planetary nebula.)
33 A hydrogen atom with its electron removed (a H+ ion in other words) is actually a
(proton.)
22 Neutron stars are often observed as
(pulsars
The period of a proto-starís evolution when its size and brightness decrease just before the ignition of nuclear reactions in its core is called
(the Tau Tauri phase.)
44 The First red giant phase of a star is caused by
(the exhaustion of hydrogen at its core.)
28 For an eclipsing spectroscopic binary star system, we can determine
(the masses and diameters of both stars in the system.)
48 Stellar Parallax is caused by
(the motion of the Earth around the Sun.)
5 The position of a protostar on an HR diagram changes because
(the size and temperature of the protostar change.)
46 The diffraction limit of a telescope refers to the effect of
(the wavelength of light.)
40 When the core of a star collapses while inside the star, the result is a
(type II supernova.)
49 A mirror that is shaped like a shallow bowl sitting on the table with its open end facing up will focus light that comes
(vertically down from above.)
8 Which of the following magnitudes corresponds to the brightest star?
-1.5
Which of the following magnitudes corresponds to the brightest star? A -1.2 B -2.6 C -4.1 D -1.0 E -4.2
-4.2
17 Barnardís star is a near neighbor of the Sun whose properties we know quite well. It is a type M4V with absolute magnitude 13.22. Suppose that another star of spectral type M4V is observed to have apparent magnitude 8.22. How far away is it?
. (1 parsec.
21 A star with a distance modulus of zero is at a distance of
. (10 parsecs
19 Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude ñ3. If the starís apparent magnitude is found to be 7, how far away is it?
. (1000 parsecs
20 The star 36-Ophiuchus is six parsecs from our Sun. The light from this star in the ìserpent holderîconstellation has been traveling for approximately
. (20 years
18 The violet lines in the Hydrogen spectrum are normally seen with wavelengths 410 nm and 434 nm. In the light of a star that is moving toward us, we might expect to see those lines at wavelengths of
. (400 nm and 424 nm
16 High protostellar winds of ejected gas occur when the protostar is in the
. (Tau Tauri phase.
6 13 In a particular binary star system, we are only able to determine a minimum mass for each star and cannot determine the angle between our line of sight and the plane of the starsíorbits. This system is most likely
. (a spectroscopic binary system
15 Adaptive optics is used to correct telescopes for
. (atmospheric turbulence
26 Which of the following particles has the smallest mass
. (electron.
25 A star with an apparent magnitude of 8.4 and an absolute magnitude of -1.0 would appear in our sky as a star
. (that is visible only with a telescope
24 The velocity of a wave is defined to be
. (the distance traveled by a crest divided by the time taken.
23 In order to use spectroscopic parallax to find the distance to a star, you need to know
. (the spectral type and luminosity class (B2V for example) and the apparent magnitude
14 The diffraction limit of a telescope refers to the effect of
. (the wavelength of light
The mass of a carbon atom is 12.00amu while the mass of a deuterium atom is 2.014amu. If a gamma ray photon splits a carbon atom into six deuterium atoms, how much energy is converted into mass?
0.084amu
A star is seen to move by 0.8 seconds of arc between March 1, 1999 and September 1, 1999 and then back to its starting point on March 1, 2000. What is the parallax angle for this star?
0.4 seconds of arc.
Barnard's star is a near neighbor of the Sun whose properties we know quite well. It is a type M4V with absolute magnitude 13.22. Suppose that another star of spectral type M4V is observed to have apparent magnitude 8.22. How far away is it?
1 parsec.
The star Tau Ceti has moved across the sky by 1922 seconds of arc during the last thousand years, more than a half of a degree of arc. Its proper motion is closest to
1.9265′′/yr.
Cruising far from the Sun, we notice that the Sun's apparent brightness has dimmed to 10 watts per square meter. We know that the apparent brightness at a distance of 1au is 1000 watts per square meter. How far from the Sun are we?
10 au
Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude --3. If the star's apparent magnitude is found to be 7, how far away is it?
1000 parsecs.
12 A star at a distance of 10,000pc should have an apparent brightness equal to its absolute brightness multiplied by
10^-6
A star at a distance of 1000pc should have an apparent brightness equal to its absolute brightness multiplied by
10⁻⁴.
The star 61-Cygni is 3.3 parsecs from our Sun. The light from this star in the "serpent holder" constellation has been traveling for approximately
11 years.
Suppose that a sound wave has a wavelength of 12 meters and a frequency of 1Hz. What is the speed of sound?
12 m/s
28 A star whose apparent brightness is 10^-4 times that of a sixth magnitude star would have magnitude
16
The star epsilon-Eridani shows a heliocentric stellar parallax near 1/3 seconds of arc. The distance from our Sun to epsilon-Eridani is near
3 parsecs.
Our own Sun has an absolute visual magnitude of 4.8. A starship that travels 10 parsecs from our Sun and looks back at the Sun will see it as having apparent visual magnitude
4.8.
The violet lines in the Hydrogen spectrum are normally seen with wavelengths 410 nm and 434 nm. In the light of a star that is moving toward us, we might expect to see those lines at wavelengths of
400 nm and 424 nm
7 The velocity of sound waves is roughly the same for all wavelengths. Suppose that a sound wave has a wavelength of one meter and a frequency of 1000Hz. The wavelength of a 250Hz sound wave would then be
4m
You hear a 1000Hz tone from a radio that is 20 feet away from you and listen for 5 seconds. How many pressure maxima pass by your ear?
5000
31 Which of the following spectral classes corresponds to the second highest surface temperature (on this list)?
A
Of all the things that might go wrong with distances found by using the method that astronmers refer to as the "distance ladder," which of these is the one that an astronomer would say is most likely?
Distant objects are not behaving the same as nearby objects.
9 In the Hertzsprung-Russell Diagram shown, which point represents a star of type B with absolute magnitude -5?
E
6 Which of the following spectral types corresponds to the star with the highest surface temperature?
F0
Which of the following spectral classes corresponds to the second lowest surface temperature (on this list)? A. A B. B C. F D. G E. K
G
Which of the following spectral types corresponds to the star with the lowest surface temperature? A G0 B G5 C F0 D F5
G5
Which of the following spectral types would you expect to look red in color? A. A B. F C. G D. M
M
High protostellar winds of ejected gas occur when the protostar is in the
Tau Tauri phase.
The star Wemadeit shows a stellar parallax angle of 0.3 seconds of arc while the star Waytoofar shows a stellar parallax angle of 0.4 seconds of arc. From this, you can conclude that
Waytoofar is closer to our Sun than Wemadeit.
36 The object Gliese 229B glows in the infrared but is much cooler and dimmer than a class M star and shows traces of lithium that a normal star would quickly burn up in the nuclear reaction that occurs in its core. This object is most likely
a brown dwarf
The object Gliese 229B glows in the infrared but is much cooler and dimmer than a class M star and shows traces of lithium that a normal star would quickly burn up in the nuclear reaction that occurs in its core. This object is most likely
a brown dwarf.
30 We see what appears to be a single star. However, when the light from the star is put through a spectrometer, we see two distinct spectra, shifting back and forth. The star is actually
a double-line spectroscopic binary system
We see what appears to be a single star. However, when the light from the star is put through a spectrometer, we see two distinct spectra, shifting back and forth. The star is actually
a double-line spectroscopic binary system.
Which of the following stars or star systems could possibly give rise to a nova:
a white dwarf in orbit around a red giant.
A type Ia supernova occurs when
a white-dwarf begins to collapse.
A star that evolves off the main sequence in about 10 million years probably has
about 20 times the mass of our Sun.
When the iron nuclei in the core of an evolved high-mass star start to come apart, they
absorb energy and limit the core temperature.
The luminosity class of a star is
an indication of the broadening of its spectral lines.
The main reason that telescope mirrors can be much larger than lenses is that the mirrors
are lighter because they are thinner.
27 In a Hertzsprung-Russell diagram,white dwarf stars such as Sirius B are
at the lower left
When we use a Hertzsprung-Russelll plot to describe the evolution of a collapsing gas cloud to a protostar and then to a regular star, we find that the object's position on the plot
begins far from the main sequence and moves onto it, where it stops
A star that forms an iron core most likely has a mass of
between 15 and 20 solar masses.
When nuclear fusion reactions stop in a star similar to our own Sun, the star's outer layers
blow off as a planetary nebula.
The explosive ignition of a star's helium core is called a
helium flash.
To measure the heliocentric stellar parallax of a star, you mostly need a telescope with
high resolving power.
35 In the Hertzsprung-Russell Diagram, a main sequence star would not be found
in the upper right or lower left
Stars with more than 15 times the mass of our Sun usually evolve off the main sequence along a path in the HR diagram that
is mostly horizontal.
Suppose that a star has a spectrum that includes red, blue, and violet lines spaced in the pattern of the lines from hydrogen but the red line is has a wavelength of 650 nm instead of the usual 656 nm. From this evidence, you can conclude that the star is
moving toward us.
The gravitational energy that is released when the core of a massive star collapses is usually
much larger than the nuclear energy that the star has generated.
The mass of Barnard's Star is about 1/6 the mass of our own Sun. Our Sun is expected to have a total life span of about 10 billion years. The life span of Barnard's Star is expected to be
much longer.
The first signal received from the 1987 supernova SN1987A came in the form of
neutrinos.
Consider a light source whose absolute magnitude can be deduced from the properties of the light that reaches us from that source. Astronomers often refer to this sort of object as a
standard candle
In the core of a high-mass star, the formation of `degenerate neutron matter' which consists entirely of neutrons that touch one another
starts a supernova explosion.
Think of the `front' of a telescope as the end that light enters. A telescope with Newtonian Focus has the eyepiece
sticking out the side near the front.
31 When the hydrogen fuel runs out at the center of a main sequence star, the star
swells up and becomes a red giant
When the hydrogen fuel runs out at the center of a main sequence star, the star
swells up and its surface temperature decreases.
33 The average energy of motion of an atom or molecule in a gas is called its
temperature
To calculate the velocity of a wave, you need to know
the distance traveled by a wave crest and the time taken.
A converging lens will send light rays that are parallel to the axis through
the focal point of the lens.
For an eclipsing spectroscopic binary star system, we can determine
the masses and diameters of both stars in the system.
For a visual binary star system, we can determine
the masses of both stars in the system.
The first indication that Cygnus X-1 might be a black hole was.
the rapid fluctuations in its X-rays.
A normal Helium nucleus consists of two protons and two neutrons. The protons actually repel each other because they have the same charge. The main force that holds this nucleus together is
the strong force.
32 Because mirrors only use one surface, they have a big advantage over lenses: They can be
thinner and larger in diameter.
In a Hertzsprung-Russell diagram, the surface temperature of stars increases going
to the left.
