ASTRON 3 - Week 3
Which of the following apparent magnitudes corresponds to the brightest object?
-1.24
How many stars (other than the Sun) have a stellar parallax greater than one second of arc?
0
If a star is at a distance of 25 pc, its parallax angle, p will be
0.04 pc
Which of the following stellar masses is not possible?
0.04 solar masses
When four protons collide to form helium, what fraction of the original mass of the protons is converted to energy?
0.7%
Which of the following main sequence stars would have the largest radius?
10 solar masses
If stellar parallax can be measured to a precision of about 0.01 arcsec using telescopes on the Earth to observe stars, to what distance does this correspond in space?
100 pc
Stars like our Sun constitute 7 % of the stars in the galaxy. Assuming that there are 400 billion stars in our galaxy, approximately how many solar type stars are there?
28 billion
How many different types of neutrino are there?
3
The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?
32.6 ly
Which of the following surface temperatures would most closely correspond to an orange star?
4300 K
The percentage (by mass) of the Sun that is hydrogen is about:
74%
Sirius, visually the brightest star in our sky, has an apparent magnitude of about -1.5, whereas the Andromeda galaxy has an apparent magnitude of about +3.5. What is the ratio of their brightness, as seen by Earth bound observers?
Andromeda is 100 times fainter than Sirius.
Which of the following four spectral classifications represents the hottest stellar surface temperature?
B
Which of the following would be the least powerful solar flare?
B7
Why does the observation of spectral emission from a highly ionized atom such as iron, Fe+13, with 13 electrons missing, indicate very high gas temperatures?
Collisions that remove this number of electrons must be very energetic between fast-moving atoms.
Which is the most violent form of activity observed on the Sun?
Coronal Mass Ejections
What is the physical reason for the appearance of periodic splitting and recombining of spectral lines in the spectra of binary stars?
Doppler shift of light from stars orbiting each other, moving toward and away from Earth during this orbital motion
A emission nebula is made of a cool, low density gas.
False
A star with an apparent magnitude of 7.67 is visible with the naked eye.
False
A star's true motion through space is called its tangential velocity.
False
If you were to place a typical interstellar dust grain in your hand you would easily be able to see it.
False
Most of the Sun's energy output originates from active regions on the Sun.
False
Mostly red light is scattered by dust in diffuse clouds.
False
Neutrons and neutrinos are the same thing.
False
Our Sun is an unusual star and not very common in the galaxy.
False
Photoionization is the process by which a molecule is broken apart by a high energy photon.
False
Space is a perfect vacuum.
False
The Sun is not a star because it looks very different to the other stars in the sky.
False
The smallest stars are much larger than the Earth.
False
The speed of a star in km/s measured perpendicular to the line of sight is known as its proper moton.
False
Very high mass stars at the limit of being stable are known as brown dwarfs.
False
The ionization symbol for an iron atom that has lost three electrons is
Fe IV
The star α Centauri C and the star Groombridge 34 B have the same apparent magnitude, but α Centauri C is 1.3 pc away from Earth, whereas Groombridge 34 B is 3.5 pc away. What is the luminosity of Groombridge 34 B compared to that of α Centauri C?
Groombridge 34 B is more luminous than α Centauri C
Which is the most common interstellar molecule?
H2
Which one of the following statements is correct for an isolated star (i.e., a star that is not in a binary star system)?
It is not possible to measure the star's mass accurately.
Where is the chromosphere on the Sun?
It is the layer above the visible surface of the Sun.
Which of the following main sequence stars would have the lowest mass?
K5
After hydrogen and helium, what is the next most abundant element in the Sun?
Oxygen
Two stars have the same apparent brightness. If Star 1 has a surface temperature of 5000 K and Star 2 has a surface temperature of 3000 K. Given this, we know that
Star 1 will be brighter in the B filter than Star 2
What condition is necessary for us to see eclipses of stars in binary star systems?
The line of sight from Earth to the star system must be in or very close to the orbital plane of the stars
When two protons and two neutrons combine to form 4He, it is found that this helium nucleus is less massive than the sum of the four original particles used to construct it. What is the significance of this?
The lost mass is transferred into energy
How does the Sun's overall magnetic field behave?
The northern and southern hemispheres have opposite magnetic polarity, and this polarity reverses every 11 years
How does the Sun's overall magnetic field behave?
The northern and southern hemispheres have opposite magnetic polarity, and this polarity reverses every 11 years.
Measurements of the brightness of a distant star through two filters indicate that the star is brightest in B, and faintest in V. What conclusion can be drawn from this information, assuming no absorption of light between the star and Earth?
The star has a very high surface temperature.
Measurements indicate that a certain star has a very high intrinsic brightness (100,000 times as bright as our Sun) and yet is relatively cool (3500 K). How can this be?
The star must be very large.
Of two stars of spectral class B5, one has broad hydrogen lines and the other has narrow hydrogen lines. How do these stars differ physically?
The star with the narrow lines is a giant or supergiant, and the star with the broad lines is a main-sequence star.
For hydrogen absorption lines to show up strongly in stellar spectra, significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level. What does the appearance of such lines in a stellar spectrum indicate about conditions on the star surface?
The temperature must be high enough to excite the electrons to this level by collisions but not high enough to ionize the atoms.
How does the temperature inside the umbra of a sunspot compare to that of the solar photosphere outside the sunspot?
The umbra is about 1500 K cooler
How does the temperature inside the umbra of a sunspot compare to that of the solar photosphere outside the sunspot?
The umbra is about 1500 K cooler.
How do two stars in a binary system orbit each other?
They both follow elliptical orbits around a common point between the stars.
What happens to the neutrinos produced by the nuclear reactions in the core of the Sun?
They escape from the Sun into space.
Which molecule produces the spectral absorption bands that are prominent in the spectrum of a cool M-type star?
TiO—titanium oxide
If you were to come back to Earth in 100,000 years, the pattern of stars in the Big Dipper would not look the same as it does today.
True
Infrared radiation can escape from a dark nebula.
True
Interstellar diffuse nebulae can cause us to overestimate the distances to stars.
True
Most interstellar dust grains are not spherical.
True
The Sun is the ultimate source of energy for life on the surface of the Earth.
True
The average density of matter in the interstellar medium is much lower than the density of the highest vacuums produced in laboratories on Earth.
True
The radial velocity of a star in measured using the Doppler shift.
True
The speed of a star in km/s measured along the line of sight is known as its radial velocity.
True
f two stars have the same surface temperature, the more luminous star will be larger.
True
Sirius, in Canis Major (the large hunting dog of Orion), is the brightest star in the winter night sky. It has a parallax angle of 0.38 seconds of arc. Orion's other hunting dog, Canis Minor, has as its brightest star Procyon, with a parallax angle of 0.29 seconds of arc. Vega, in Lyra the Lyre (Harp), is the brightest star in the summer night sky. It has a parallax angle of 0.13 seconds of arc. Which of these stars is farthest away?
Vega
What is the Zeeman effect?
When a light source is located in a magnetic field, the spectral lines it emits are split into two or more components.
Which of the following would be the most powerful solar flare?
X8
The appearance of the visible spectrum of the Sun, when its light is separated in its component colors, is
a continuous bright spectrum, crossed by thousands of dark absorption lines.
What is a plasma?
a gas-like mixture of ions and electrons
The solar wind is
a gentle outflow of solar material, mostly protons and electrons, always moving outward from the Sun.
A particular star is at a distance of 20 pc from the Earth. For this star, the apparent magnitude would be
a larger number than the absolute magnitude.
Which of the following is NOT a consequence of a coronal mass ejection event from the Sun, if the mass ejection is aimed toward the Earth?
a major hurricane
What is the name of a large loop of bright gas extending outward from the edge of the Sun?
a prominence
Early neutrino telescopes detected a rate of solar neutrinos arriving at the Earth that is
about 1/3 the predicted rate
How many second-magnitude stars would be required to match the light intensity from a first-magnitude star?
about 2.5
How much longer can the Sun continue to generate energy by nuclear reactions in its core?
about 6 billion years
The star Elnath is classified as B7 III, and the star Al Na'ir is classified as B7 IV. This tells us that compared to Al Na'ir, Elnath is
about the same temperature, but intrinsically much brighter.
When a molecule changes its rotational energy from a low energy to a high energy it
absorbs a radio or microwave photon photon
The gas in the interstellar medium is in the form of
all three of these
Which of the following neutrino telescopes use Cherenkov radiation to detect them?
all three of these do: Super-Kamiokande IceCube Sudbury Neutrino Observatory
Parallax is the
apparent shift in position of a nearby object as we move.
The phrase "'hydrostatic equilibrium"' in the Sun refers to the
balance of gravity inward and gas pressure outward.
A star with a dominant wavelength in the ultraviolet, would appear what color to the eye?
blue
Apparent magnitude is a measure of the
brightness of a star, as seen from the Earth
The technique called photometry in stellar astronomy is the measurement of the
brightness of light from stars through several limited-bandpass filters, from which surface temperature, variability, luminosity, etc. can be determined.
The point around which two stars of unequal mass in a binary system appear to revolve is
closest to the more massive star
What quantities do we need to measure to calculate the tangential velocity of a star?
distance and proper motion
What causes the characteristic red color of an emission nebula?
electrons jumping from the n = 3 energy state to the n = 2 energy state in hydrogen atoms
When a molecule changes its vibrational energy from a high energy to a low energy it
emits an infrared photon
In the course of a sunspot cycle of about 11 years, the regions of sunspot occurrence on the Sun move
equatorward—moving from 30° to 10° latitude.
The rotation of the Sun is
fastest at the equator, slower at mid-latitudes, and slowest near the poles.
Each different type of neutrino has a different
flavor
The total amount of energy radiated per square meter from the surface of a star is defined to be its
flux
The space between stars is now known to contain
gas made up of atoms and molecules, and also dust particles.
The star Hadar has a spectral classification of B1 III. This tells us that Hadar is a
hot giant
Astronomers use the symbol H II to mean
ionized hydrogen.
A typical granule on the surface of the Sun
is about 1000 km across and lasts for a few minutes.
Approximately where is the Sun in terms of its total lifetime?
its about halfway through its life
Spicules on the solar surface are
jets of gas surging out of the photosphere of the Sun into the chromosphere, usually at supergranule boundaries.
Supergranules on the Sun are
large and long-lived convecting gas cells, containing hundreds of ordinary granules.
In order to be able to measure the size of a star directly we need the star to be
large in size and close to the Sun
At visible wavelengths, what type of intensity distribution does one see at the edge or limb of the Sun?
limb darkening
Which of the following best describes a dark nebula?
low temperature, high mass, high density
Simple relationships exist between mass and luminosity for
main-sequence stars and brown dwarfs.
Spectroscopic parallax is the
method of calculating the distance to a star by using the spectral-luminosity class of the star, its apparent brightness, and the inverse-square law.
The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4. From this information, we can say for certain that Alderamin is
more than 10 parsecs away.
Astronomers use the symbol H I to mean
neutral Hydrogen
A star with a radius of half that of the Sun and a spectral type of K2 would be called a
orange dwarf
As you drive along a road, trees in the middle distance seem to shift in position relative to faraway hills. What name is given to this phenomenon?
parallax
The solar wind is ionized gas flowing outward
primarily through coronal holes.
Of the three ways in which energy is transported in nature (radiation, conduction, convection), which two are important in the Sun?
radiation and convection
What is the characteristic color of an emission nebula?
red
In recent times, one method that has been used successfully to investigate the deep interior of the Sun has been to observe
regular oscillations and fluctuations of the surface.
The blue color of a reflection nebula is produced by
selective scattering from very small dust grains.
Compared to a star in the middle of the diagram, a star in the lower left part of the Hertzsprung-Russell diagram is
smaller
In photographs, the Pleiades open star cluster is surrounded by a bluish haze. What causes this blue light?
starlight scattered from interstellar dust in the star cluster
The ratio of the brightness of a star at two different colors, blue and visual—bV/bB—is a direct measure of what property of the star?
surface temperature
What is the corona on the Sun?
the Sun's outer atmosphere
The phrase "hydrostatic equilibrium" in the Sun refers to
the balance of gravity inward and gas pressure outward.
What does apparent magnitude tell us about a star?
the brightness of a star as it appears in our sky
The mechanism at work when energy is transmitted by convection is
the mass motion of hot gases.
A luminosity function is a plot of
the number of stars in a given volume as a function of their luminosity.
Spectral classification determines a nearby star's surface temperature by examining
the pattern of spectral "absorption" lines from various atoms
Spectral classification determines a nearby star's surface temperature by examining
the pattern of spectral "absorption" lines from various atoms.
We see an emission nebula predominantly in
the red light from recombination of electrons with nuclei in ionized hydrogen.
What is the photosphere of the Sun?
the visible "surface" of the Sun
At the present time, the dominant energy source that powers the Sun is
thermonuclear fusion of hydrogen into helium in the core
The effect of interstellar dust on starlight is
to dim and redden distant stars by preferentially scattering their blue light.
An eclipsing binary system is
two stars whose combined light output when measured from Earth appears to vary periodically as the two stars move in front of one another.
Where do we find the most massive stars on the main sequence in a Hertzsprung-Russell diagram?
upper left
The radial-velocity curve of a star in a binary star system is a plot against time of the
variation of Doppler shift of its spectral lines and hence of its speed toward or away from us.
A star with a radius of 50 times that of the Sun and a spectral type of A5 would be called a
white giant
The contraction of a star (or other object) due to its own gravity generates heat. If this process, known as the Kelvin-Helmholtz contraction, were to be the source of heat energy from the Sun, then the Sun's age
would be about 25 million years
The bright stars at the center of an emission nebula are mostly
young O and B stars.
The core of the Sun, in which all the Sun's thermonuclear energy is produced, takes up about
¼ of the Sun's radius.
