Astronomy Exam 4 Gowdy
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.
Spectroscopic Parallax refers to
a method for finding distances to stars.
The idea that a supernova is preceded by a huge burst of neutrinos is
a prediction that has now been observed.
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.
When a red giant star begins to burn helium, its diameter
decreases but not to its main sequence size.
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.
Ham radio operators sometimes operate receivers for the 2 meter wavelength band. The 2 meters refers to the
distance from one maximum of the radio waves to the next.
The core of a red supergiant star stops shrinking because its
electrons touch each other.
The temperature of a gas measures the
energy of motion of its atoms or molecules.
The point at which even an outwardly directed light ray is pulled into a black hole is called the
event horizon.
Stars that are much more massive than our Sun
form faster and burn out faster.
In an evolved high-mass star, when the electrons combine with protons to form a pure neutron core, the reaction
generates a neutrino burst.
To see a large but faint object such as a nebula, you would need a telescope with large
light gathering power.
On a HR diagram, a visible white dwarf star is in the
lower left and upper right corner
When a white dwarf star collects matter from a neighboring star, fusion reactions on the surface of the white dwarf cause
novas.
A star with an absolute magnitude of 5.7 and an apparent magnitude of -1.2 would appear in our sky as a star
of dazzling brightness.
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.
A hydrogen atom with its electron removed (a H⁺ ion in other words) is actually a
proton.
Which of the following particles would be repelled by a positron?
proton.
A star that is cooler than most other stars will probably look
red.
Our Sun is a type G2V star on the main sequence. As it ages and uses up its fuel we expect it to
remain a G2V star until it leaves the main sequence.
Nuclear fusion requires high temperatures because nuclei
repel each other.
To see small but bright objects such as the ice caps on Mars, you would need a telescope with large
resolving power.
The "Little Green Men Standard Time" hypothesis for the repeating radio signals seen in 1968 was rejected partly because the repetition rate was
slowing down.
A star with an apparent magnitude of 5.7 and an absolute magnitude of -1.2 would appear in our sky as a star
that is barely visible to the naked eye.
The size of a typical white dwarf star is comparable to the size of
the Earth.
Which of the following magnitudes corresponds to the brightest star?
0.
Compared to a magnitude 6 star, a magnitude 1 star would be
100 times as bright.
Which of the following magnitudes corresponds to the dimmest star?
+4
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
The mass of a carbon atom is 12.00amu while the mass of a deuterium atom is 2.014amu. If six deuterium atoms fuse to form a carbon atom, how much mass is converted into energy?
0.084amu
A star is seen to move by 0.2 seconds of arc between February 1, 1999 and August 1, 1999 and then back to its starting point on February 1, 2000. What is the parallax angle for this star?
0.1 seconds of arc.
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 March1, 2000. What is the parallax angle for this star?
0.4 seconds of arc.
The apparent brightness of our Sun is roughly 1000 watts per square meter. At a distance of 30 times the Earth-Sun distance, the apparent brightness of our Sun would be
1.1 watts per square meter.
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 500Hz. The wavelength of a 1000Hz sound wave would then be
1/2 m.
A star with a distance modulus of zero is at a distance of
10 parsecs.
Our Sun is expected to last for about 10 billion years. Which of these is a likely lifespan for a star with 20 times the mass of our Sun?
10-15 million years.
Cruising far from the Sun, we notice that the Sun's 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
Our Sun is a G2V star with absolute magnitude 4.8. Suppose that a star of spectral type G2V is observed to have apparent magnitude 9.8. How far away is it?
100 parsecs.
A star is observed to have an apparent brightness which is 10⁻⁴ times its absolute brightness. How far away is it?
1000 parsecs.
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 23.22. How far away is it?
1000 parsecs.
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.
Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude 4.8. If the star's apparent magnitude is found to be 14.8, how far away is it?
1000 parsecs.
A star at a distance of 10,000pc should have an apparent brightness equal to its absolute brightness multiplied by
10⁻⁶.
A star whose apparent brightness is 1/100 times that of a sixth magnitude star would have magnitude
11.
Suppose that a flash 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
Suppose that a flash of lightning from a cloud 5000 meters away is followed by a clap of thunder four seconds later. Assume that the light arrived in a negligible time and calculate the speed of the sound waves.
1250m/s
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 500Hz sound wave would then be
2 m.
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
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.
The star delta-Eridani shows a heliocentric stellar parallax of almost exactly 1/9 seconds of arc. The distance from our Sun to delta-Eridani is
9 parsecs.
In the Hertzsprung-Russelll Diagram shown, which point represents a star of type K with absolute magnitude +10?
A
Which of the following pictures is the most like the main sequence on a Hertzsprung-Russell Diagram?
A
You see a reflecting telescope with a short, stubby tube and the eyepiece at the back. This telescope uses the
Cassegrain Focus.
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.
In the Hertzsprung-Russell diagram shown, point number 2 could be a
F0 star of absolute magnitude -5.
Which of the following spectral types corresponds to the star with the lowest surface temperature?
G5
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.
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.
A spectral type G star could be a main sequence star like our own Sun or it could be one of several different types of red giant stars. Can we tell which it is just by looking at its spectrum?
Yes. The widths of the spectral lines tell us which it is.[correctchoice]<LaTeX>\correctchoice{}</LaTeX>
When an interstellar cloud fragment does not have enough mass to form a star powered by nuclear fusion, but gets hot enough to glow for a while, it is called
a brown dwarf.
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.
In a particular binary star system, we are able to determine the masses of both stars in the system as well as the angle between our line of sight and the plane of the stars' orbits but cannot determine the diameters or atmospheric compositions of the two stars. This system is most likely
a visual binary system.
A nova occurs when
a white dwarf steals fuel from a neighbor.
A type Ia supernova occurs when
a white-dwarf begins to collapse.
The first red giant stage of a one solar mass star's life usually ends with
an explosion in the helium core.
The luminosity class of a star is
an indication of the broadening of its spectral lines.
The average energy of motion of an atom or molecule in a gas is called its
temperature.
Because of the electrical repulsion between atomic nuclei, nuclear fusion happens only
at high temperatures.
A star that forms an iron core most likely has a mass of
between 15 and 20 solar masses.
High protostellar winds of ejected gas occur
between the initial contraction and the ignition of nuclear burning.
To measure the heliocentric stellar parallax of a star, you mostly need a telescope with
high resolving power.
In the Hertzsprung-Russell Diagram, a main sequence star might be found
in the lower right or upper left.
For stars on the main-sequence, stars with increasing mass have
increasing surface temperature and absolute brightness.
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 660 nm instead of the usual 656 nm. From this evidence, you can conclude that the star is
moving away from us.
The mass of Betelgeuse is about 20 times 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 Betelgeuse is expected to be
much shorter.
The Earth's motion around the Sun causes
nearby stars to shift back and forth once a year
A spectroscopic binary star system is one in which we see
spectral lines shifting back and forth.
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.
When the hydrogen fuel runs out at the center of a main sequence star, the star
swells up and becomes a red giant.
During the Tau Tauri phase of a protostar's evolution,
the brightness decreases.
The 'helium flash' refers to
the explosive ignition of a star's helium core.
A converging lens will send light rays that are parallel to the axis through
the focal point of the lens.
We can see the star Sirius and its companion, the Pup, moving around each other. Careful measurement of this motion can provide
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.
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.
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.
In a Hertzsprung-Russell diagram, the absolute brightness of stars increases going
upward.
A mirror that is shaped like a shallow bowl sitting on a glass table with its open end facing up will focus light that comes
vertically down from above.
