astronomy exam 4 (ch 13 - 16)
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
Barnard's Star shows a heliocentric stellar parallax near 1/2 seconds of arc. The distance from our Sun to Barnard's Star is
2 parsecs
Which of the following objects is closest in size to a black hole formed from the collapse of a star?
a neutron star
A steady X-ray signal with sudden bursts lasting a few seconds each is probably caused by
a neutron star in a 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 that its spectrum is shifting back and forth. The star is most likely
a single-line spectroscopic binary system.
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 stars' orbits. This system is most likely
a spectroscopic binary system.
Type II supernovas have the following properties:
a spectrum with hydrogen lines and a variable maximum brightness.
The intense magnetic field of the Crab pulsar causes its rate of spin to
decrease
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.
An atom of ordinary hydrogen consists of a proton and
electron
Which of the following particles would be electrically attracted by a positron?
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
A star leaves the horizontal branch in the HR diagram when
it runs out of helium at its core.
When a star first moves off the main sequence,
its surface temperature drops and its brightness first stays about the same and then increases.
To see a large but faint object such as a nebula, you would need a telescope with large
light gathering power.
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 increases, its molecules
move faster
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
A converging lens will send the light from a distant star through a point
on the focal plane of the lens
Which of the following particles would be attracted to a neutron through the strong force?
proton
Neutron stars are often observed as
pulsars
The upper right of a Hertzsprung-Russell diagram is where one finds
red giant stars
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.
When a red giant star begins to burn helium, it
returns part way to the main sequence in an HR diagram
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.
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
A star is seen to move by 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?
1 seconds of arc.
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 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.
The apparent brightness of our Sun is roughly 1000 watts per square meter. Saturn is at roughly 10 astronomical units from our Sun (slightly less actually). Viewed from Saturn, the apparent brightness of our Sun would be
10 watts per square meter.
The diameter of a white dwarf star might be
10,000 miles.
A star is found to have absolute magnitude 9 and apparent magnitude 24. How far away is it?
10,000 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 100pc should have an apparent brightness equal to its absolute brightness multiplied by
10⁻²
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
You hear a 1000Hz tone from a radio that is 10 feet away from you and listen for 4 seconds. How many pressure maxima pass by your ear?
4000
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 away from us, we might expect to see those lines at wavelengths of
415 nm and 439 nm
A star whose apparent brightness is 1/100 that of a first magnitude star would have magnitude
6
The star Vega is 25 parsecs from our Sun. The light from Vega has been traveling for about
80 years.
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.
A type Ia supernova occurs when
A white dwarf star begins to collapse
What full spectral type corresponds to a star on the main sequence?
B4V
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.
Which of the following star-like objects would most likely be considered to be a brown dwarf?
Gliese 229B, luminosity and temperature both below type M9V.
Name the spectral classes from highest to lowest surface temperature
O B A F G K M (oh be a fine girl kiss me)
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.
For a star to give rise to a Nova, the star must be
a member of a multiple star 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 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.
In a particular binary star system, we are able to determine the masses and diameters of both stars This system is most likely
an eclipsing spectroscopic binary system
The onset of Helium burning at the core of a star normally begins with
an explosion in the helium core.
Because of the electrical repulsion between atomic nuclei, nuclear fusion happens only
at high temperatures
Think of the `front' of a telescope as the end that light enters. A telescope with Cassegrain Focus has the eyepiece
at the back of the telescope.
Adaptive optics is used to correct telescopes for
atmospheric turbulence.
When nuclear fusion reactions stop in a star similar to our own Sun, the star
becomes a white dwarf.
A star that forms an iron core most likely has a mass of
between 15 and 20 solar masses.
A star that is hotter than most other stars will probably look
blue
The light from a new-born white dwarf star will most likely be
blue
A converging mirror of the sort that is used to collect light in astronomical telescopes
has a focal point on the same side of the mirror as the light source.
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.
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.
A star leaves the main sequence when
it runs out of Hydrogen at its core
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 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 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 first signal received from the 1987 supernova SN1987A came in the form of
neutrinos
Which of the following particles has almost the same mass as a proton?
neutron
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.
The period of a proto-star's evolution when its size and brightness decrease just before the ignition of nuclear reactions in its core is called
the Tau Tauri phase.
Electron degenerate matter is matter in which
the electrons are touching each other so that they cannot be compressed.
Stellar Parallax is caused by
the motion of the Earth around the Sun.
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 absolute brightness of stars increases going
upward
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
