ASTR 104 – Winter 2007 Intersession – Test 2 answers
Questions on material that we have not covered are greyed out. Blue questions refer to test 3 material.
(1) How can we find the distance to the nearest stars?
– By looking at their size in a photographic image.
– By measuring the amount of starlight that reaches us.
– By looking at their color.
d. By measuring their parallax.
(2) Approximately how far from us is the nearest star (other than the Sun)?
– 4 million miles.
– 4 astronomical units.
c. 4 light years.
– 4 million light years.
(3) Approximately how fast do stars move around us?
– All stars move at a few miles per hour.
– Most stars move at 50-60 miles per hour.
c. Most stars move at tens of thousands of miles per hour.
– All stars move at the speed of light.
(4) Can we tell how large a star is from its size on a photograph?
– Yes, we just need to magnify the photograph and use a ruler.
– Yes, but we have to take into account how far the star is.
– No, because all stars produce images of the same size.
d. No, almost always a large image only means that the star is very bright.
(5) How can we find out the temperature of a star?
a. From the wavelength at which it emits most of its radiation.
– From the amount by which its spectral lines are redshifted.
– By comparing its apparent brightness and luminosity.
– By measuring the rate at which its light flickers.
(6) If we say that a star is among the "cooler" ones, what is its
surface temperature, approximately?
– 10 K.
b. 3000 K.
– 30,000 K.
– 10 million K.
(7) What is the main sequence?
a. A band across the HR diagram where most stars lie.
– The sequence of stages any star goes through in its lifetime.
– The sequence of stages a mid-size star like the Sun goes through.
– The set of letters O, B, A, F, G, K, M.
(8) Which stars live longer?
– All stars last about the same amount of time.
– More massive stars, because they have more fuel available.
c. Less massive stars, because they burn more slowly.
– Stars live forever, once they are able to reach the main sequence.
(9) Which of the following have we not mentioned as an example of a binary
star?
– Sirius.
– Mizar.
– Algol.
d. Rigel.
(10) Which of the following things do you see when looking at an eclipsing
binary star system?
– A two-star system in which both stars can be seen.
b. A star from which the amount of light we receive changes in time.
– One for which the frequency of the spectral lines changes in time.
– One whose visible spectrum shows both emission and absorption lines.
(11) What are the Pleiades?
– Two stars in a very close, tight binary system.
– The four stars at the center of the Orion nebula.
c. An open cluster of stars in Taurus.
– A globular cluster of stars in Taurus.
(12) Which of these contains more stars?
– The Alpha Centauri system.
– The Solar System.
– An open cluster
d. A globular cluster.
(13) Why would we want to plot all stars of one particular cluster
together in an HR diagram?
– Because it allows us to find out how far the cluster is.
b. Because it allows us to find out the age of the cluster.
– Because it allows us to find out how hot each star in the
cluster is.
– Because it allows us to find out how bright each star in the
cluster is.
(14) Which star clusters are usually older, in our galaxy?
– Open clusters, which have opened up and lost stars over time.
b. Globular clusters, most of which are more than 10 billion
years old.
– They are equally old, but open clusters just happen to be
smaller.
– There is no general pattern, both types can be either young
or old.
(15) Why do we see so many stars in close pairs or in clusters
in the sky?
– Because when viewed from Earth they appear to be close
to each other.
b. Because they form together in large clouds that break
into fragments.
– Because stars are so massive that they attract each other
over large distances.
– Because many stars break up into smaller stars when they
explode.
(16) How large are the clouds that collapse to form stars,
initially?
– Tens of millions of km.
– Several astronomical units.
c. Tens of light years.
– Several millions of parsecs.
(17) Which one of the following best describes a protostar?
– The first star that is formed in a given star cluster.
– A totally ionized star, made only of protons without
electrons.
– An unstable star, that has already left the main sequence.
d. A hot contracting cloud fragment in the process of
becoming a star.
(18) Do stars shine forever?
– Yes.
– Yes, unless other stars hit them and knock them off
the main sequence.
– Yes, unless thick clouds of gas and dust surround
and obscure them.
d. No, over periods of millions or billions of years
they run out of fuel.
(19) What is the first element produced from hydrogen
fusion inside stars?
a. Helium.
– Carbon.
– Iron.
– Plutonium.
(20) Why do stars swell up
to much larger sizes after the main sequence stage
in
their lives?
– Because the core grows in size and pushes the
other layers outwards.
– Because the temperature and rate of energy production
in the core increase.
c. Because the core shrinks, the layer around it
contracts, and it becomes hotter.
– Because what makes them leave the main sequence
is matter from another star.
(21) What would you call an object that is not
quite massive enough to become a star?
– A white dwarf.
b. A brown dwarf.
– A white hole.
– A black hole.
(22) What is a planetary nebula?
– A ring of gas and dust surrounding a newly
formed planet.
– The cloud-like debris of a planet shattered
by a collision.
c. An expanding, round shell of gas ejected
by an old low-mass star.
– A nebula which is too small to form stars,
but may form planets instead.
(23) What is a nova?
– A new star that has just formed out of a
collapsing cloud.
– A star that is being completely blown
away by an explosion.
c. A white dwarf in a binary system whose
surface flares up.
– A galaxy whose core has just become a
supermassive black hole.
(24) How often do we see novas in our galaxy?
a. Several every year.
– Once every century
on average.
– We have only seen one so far.
– We
have only seen them in other galaxies.
(25) What is the difference between type
I and type II supernovas?
– Type I supernovas are 100 times as
bright as type II supernovas.
b. Type I supernovas are binary stars,
type II single massive stars.
– Type I supernovas emit visible light,
type II only radio waves.
– Type I supernovas produce interstellar
gas, type II produce dust.
(26) How often do supernovae normally
occur inside our galaxy?
– We see several every year.
b. We expect to see one every 100 years
or so on average.
– Only one every 30-40 million years.
– Never; supernovas only occur in
young, distant galaxies.
(27) What is a neutron star?
a. The remnant of a massive star after
a supernova explosion.
– A star that is too small to start
burning hydrogen in its core.
– The hottest and brightest kind
of star on the main sequence.
– A star in which the atoms are
not ionized and remain neutral.
(28) What is a pulsar?
a. A rotating neutron star emitting
a beam of radio waves.
– A neutron star that pulsates
by expanding and contracting.
– A neutron star orbiting around
a white dwarf and eclipsing it.
– A Cepheid variable that is collapsing
to form a white dwarf.
(29) Which of the following is
an example of a pulsar?
– The center of the Milky Way
galaxy.
b. The center of the M1 (Crab)
nebula.
– The center of the M87 globular
cluster.
– The center of the Orion Nebula.
(30) According to Einstein's
theory of relativity, what
produces gravitational
forces?
a. What we call gravity is
caused by the curvature of
spacetime.
– What we call gravity is
actually due to the magnetic
field of
a star.
– Gravity is caused by intense
radiation coming from hot objects.
– Gravity is the force between
two massive objects a certain
distance apart.
(31) What is an event horizon?
a. The surface of a black hole,
from inside which not even
light can escape.
– The farthest distance
you would see if you were
standing
on a black
hole.
– The edge of a galaxy,
beyond which there is only
dark matter.
– The farthest distance
you can see without interstellar
matter
blocking the view.
(32) What would happen to
you if you stood on the
surface of a black
hole?
a. The surface is not an
actual place to stand on,
and you
would just fall
inward.
– Because black holes
spin very fast you would
be thrown
outward
at great
speed.
– You would be permanently
stuck on the surface, unable
to see
or to lift
your
feet.
– The strong gravity of
the black hole would flatten
you
down on
its surface.
(33) Which one of the following
is a way for black holes
to form?
– A star is surrounded
by so much dust that
no light
can shine
through.
– A star is formed from
a cloud of dark matter
instead of regular
matter.
c. A star collapses to
such a small size that
its gravity
prevents
light
from
escaping.
– A star cools down past
the white dwarf stage and
in the
end emits
no light at
all.
(34) Are there any
black holes in our galaxy?
– No, we don't have good
evidence for any black
holes anywhere
yet.
– No, they have been
seen only in some of
the most
distant galaxies.
– Only one, a supermassive
black hole in the core
of the galaxy.
d. Yes, there is a massive
one at the core plus
many smaller ones.
(35) What are the two
most common elements
in interstellar
space?
a. Hydrogen and helium.
– Helium and oxygen.
– Hydrogen and carbon.
– Carbon and oxygen.
(36) On average, how
much matter is there
in interstellar
space?
a. 1 atom per cubic
centimeter.
– 10,000
atoms per cubic
centimeter.
– 10 million atoms
per cubic centimeter.
– 100 billion
atoms per cubic
centimeter.
(37) What effect
does gas in interstellar
clouds have on
starlight?
– It dims and
reddens the light.
– It bends and focuses
the light.
– It causes light
to be blueshifted.
d.
It absorbs
light at some
specific wavelengths.
(38) What is the
name of the galaxy
we are
in?
– The Solar
System.
– The
Local Group.
c. The Milky
Way galaxy.
– The
Andromeda galaxy.
(39) How many
stars are in
our galaxy?
– One.
– Several hundreds.
– Hundreds
of thousands.
d.
About 100 billion.
(40) How do
we know the
size
of the halo
of our
galaxy?
– We look
at nearby
galaxies,
and assume
they are
roughly the
same.
– We observe
the 21-cm
wavelength
radio waves
from it.
– We send
out radio
waves and
wait for
them to bounce
back
to us.
d. We map
the positions
of
the globular
clusters
in our galaxy.