Transcript Unit 1 - UW Madison Astronomy Department

If the Sun were 9 times more heavier than it is, while the
Earth were still 1 A.U. (Astronomical Unit) away from it, the
Earth year would be:
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a. 1/3 year;
b. 9 years;
c. 3 years;
d. none of the above
How is the distance to a star related to its parallax?
A. Distance is proportional to parallax
B. Distance is inversely proportional to parallax
C. Distance is proportional to parallax squared
D. Distance is inversely proportional to parallax squared
Sun spots are dark
• A. only in comparison with the surrounding
material
• B. because they contain heavy elements
• C. because magnetic fields are dark
• D. because magnetic fields absorb light
Sun spots are cooler than surrounding gas
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A. as they emit more efficiently than surrounding gas
B. as magnetic field impede thermal conduction
C. as nuclear reactions are suppressed by in sun spots
D. as magnetic field undergoes reconnection there
What is the difference between brightness and
luminosity?
a. There are different names for the same thing
b. Brightness is how we see a star, luminosity is how much
light it emits
c. Luminosity is the measure of the size of the star, brightness
is the measure the age the star
d. None of the above
The limit on the resolution of a large groundbased
telescope is due to
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a. diffraction
b. refraction
c. the focal length
d. atmospheric seeing
Arrays of radio telescopes can produce much better
resolution than single-dish telescopes because they
work on the principle of
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a. reflection
b. refraction
c. diffraction
d. interference
The biggest problem for infrared observations is
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a. smog
b. carbon dioxide
c. water wapor
d. light polution
Solar activity reflected by the number of sunspots is
believed to influence the climate on Earth as
• A. when Sun has more sunspots it radiates less heat
• B. sunspots inhibit nuclear reactions in the Sun
• C. the number of energetic particles interacting
with Earth atmosphere changes
• D. sunspots affect the Earth orbit
Sun’s magnetism is due to
• A. iron core of the Sun
• B. heating of Corona by energetic particles generated
during Solar Flares
• C. generation of magnetic fields via fluid+magnetic
field motions
• D. neutrino flows coming from the Sun’s core
Standard candle is
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A. Astronomical instrument to measure spectra
B. Source of emission with known luminosity
C. Source of neutrino generation
D. Focus of laser beam used to correct for turbulence
in atmosphere
O stars show weak hydrogen absorption lines as
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A. they do not contain hydrogen
B. their magnetic fields are too strong
C. they are hot
D. they are very cold
Jets are launched from young stars
A. Due to nuclear blasts in the star
B. Due to magnetic forces acting on accreting material
C. Due to radiation forces from the hot nuclear burning star core
D. Due to gravitational pull of the star on the jet material
Our Sun will eventually
A. Become white dwarf
B. Explode as a supernova
C. Become a protostar
D. Become a black hole
The spectral type of a star is most directly related to
its
a. Absolute magnitude
b. Surface temperature
c. Size or radius
d. Luminocity
Which two vital parameters are used to describe the
systematics of a group of stars in the HR diagram?
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a. Mass and weight
b. Luminocity and radius
c. Surface temperature and mass
d. Luminocity and surface temperature
CNO cycle happens
A. In protostars as they are not hot enough
B. In the stars similar to our Sun
C. In high mass stars with very hot core
D. In fully convective low mass stars
Why is it that the majority of stars in the sky are in
the main sequence phase of their lives?
• a. Because this is the only phase that is common to all
stars
• b. because most stars die at the end of main sequence
phase
• c. because most stars in the scy are created at about
the same time
• d. because this is the longest lasting phase in each
star life
When a star leaves the main sequence and expands
towards the red giant region, what is happening
inside the star?
• a. Hydrogen burning is taking place in a spherical
shell just outside the core; the core itself is almost
pure helium.
• b. Helium is being converted into carbon and oxygen
in the core.
• c. Helium burning is taking place in a spherical shell
just outside the core.
• d. hydrogen burning is taking place in a spherical
shell, while the core has not yet started thermonuclear
reactions and still mostly hydrogen.
A Cepheid variable is
• a. a low mas red giant that varies in size and
brightness in an irregular way
• b. a big planet
• c. a high-mass giant or supergiant star that
pulsates regularly in size and brightness
• d. a variable emission nebula near a young star
One of the reasons for pulsars to experience glitches is
A. Nuclear burning in the neutron star
B. Nuclear burning in the white dwarf
C. Cracking of the neutron star crust as it gets more round
D. Cracking of the neutron star crust as it gets more oblate
Exploding white dwarfs (supernovae type Ia) provide
good standard candle as
A. Their light curve (luminosity versus time) is the same
B. Their magnetic fields are well known
C. They produce neutron stars with known properties
D. Burning of hydrogen in white dwarfs has been
well studied theoretically
Pulsars produce observed pulses as
• A. Their surface is subject to pulsation
• B. Their magnetic fields are changing rapidly as
reconnection events take place
• C. The cone of their radiation encompasses the
observer as the neutron star rotates
• D. Accretion of material onto pulsar’s surface is
periodic
Thermal radiation emitted by isolated Black Holes can be
understood in terms of
A. Nuclear burning induced by the black hole
B. Expansion of the Universe locally near the black hole
C. Effect of the gravitational field on virtual
electron-positron pairs arising due to the quantum
mechanical energy uncertainty
D. Stopping of time in the vicinity of the black hole as the black
hole travels through space-time
Reflection nebulae are bluish as
A. Dust emits more blue light rather than red light
B. Dust scatters more blue light compared to red light
C. Hydrogen gets ionized by ambient stars
D. Magnetic fields block most of the red light
21 cm emission is due to
• A. Flipping of spin of an electron in the magnetic
field of a proton
• B. Electrostatic interaction of an electron and a proton
• C. Emission of virtual electron-positron pairs by a
proton
• D. Gravitational interaction of an electron and a
proton
As a star converts most of its hydrogen in its core into
helium, the star gets
a. less luminous and smaller
b. hotter and fainter
c. more luminous and bigger
d. less luminous and red
A hydrogen burning shell is created near the helium core
because
a. helium diffuses into the shell
b. hydrogen diffuses into the core
c. core is hot and dense
d. both a. and b.
If we observe a star cluster which has all the stars
of main sequence present, this cluster is
a. old
b. young
c. was born as a result of supernova explosion
d. both a. and c.
Gravitational lensing of light by clusters of galaxies
A. Indicates the existence of dark matter
B. Proves that the Universe has large positive curvature
C. Proves the expansion of the Universe
D. Indicates the existence of dark energy in the
Universe
Solar Flares happen due to
a. annihilation of oppositely directed magnetic fields
b. nuclear reactions on the Sun surface
c. explosions of chemicals on the Sun surface
d. comets hitting the Sun surface
A solid body (e.g. a brick of metallic iron of size 1 cm) does not emit
a distinct emission line spectrum of its constituent atoms as
a. as there are no laws for emission for solid bodies
b. quantum mechanics is not applicable to any solid body starting from the
size of
0.1 milli meter
c. atoms interact strongly in the body and do not emit independently
d. the line emission is absorbed by the atmosphere between the solid and the
observer
Magnetic pressure of magnetic field in Sun spots is compensated by
a. high gaseous pressure of the surrounding material
b. nuclear reactions in the surrounding material
c. magnetic reconnection in Solar Corona
d. all of the above
What causes the core of a star to contract during the main sequence
phase of the star’s life?
a. Helium has a larger atomic weight than hydrogen and exerts a stronger
gravitational pull on the core.
b. Convection in the outer layers carries energy out of the core more
efficiently as the star ages
c. A black hole gets created at the stellar core
d. The conversion of hydrogen into helium reduces the number of
particles in the core