ASTR 101 – Practice Test 3
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(1) What causes the collapse of a cloud that leads to star formation?
a. Gravity.
b. Heat.
c. Rotation.
d. Magnetic fields.

(2) Why do we see so many stars in clusters or binary systems?
a. 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.
c. Because they are so massive that they attract distant stars toward them.
d. Because many supernovas break up into several smaller stars when they explode.

(3) What is a protostar?
a. The first star that is formed in a given star cluster.
b. A totally ionized star, made only of protons without electrons.
c. An unstable star, that has already left the main sequence.
d. A hot contracting cloud fragment that has not become a star yet.

(4) When can a collapsed cloud fragment be called a star?
a. When the temperature in the core is more than one million degrees.
b. When nuclear reactions start occurring in its center.
c. When the temperature on its surface is more than 10 million degrees.
d. When we can see it with our telescopes.

(5) How massive are the largest stars?
a. Twice as massive as the Sun.
b. 10 times as massive as the Sun.
c. 100 times as massive as the Sun.
d. 1000 times as massive as the Sun.

(6) What is a brown dwarf?
a. A would-be star that didn't have enough mass to start burning hydrogen.
b. A white dwarf that has cooled down and does not glow so bright.
c. A white dwarf surrounded by a cloud which prevents us from seeing it.
d. A planet that is not attached to a star but moves freely in space.

(7) What is the minimal temperature in a star's core for nuclear reactions to occur?
a. 1000 K.
b. 10,000 K.
c. 10 million degrees K.
d. 10 billion degrees K.

(8) Which of the following is a good way to find newborn stars?
a. Use an infrared telescope and look at thick interstellar clouds.
b. Use an X-ray telescope and look near a supermassive black hole.
c. Use an interferometer and look inside a globular cluster.
d. Use an ultraviolet telescope and look at the brightest quasars.

(9) How do we measure motion of stars along the line of sight (radial motion)?
a. From the brightness of the light we receive from them.
b. From the red- or blue-shift of their spectral lines.
c. From the changes of their position in the sky.
d. From their location in the HR diagram.

(10) How large is the Sun's radius, compared to the Earth?
a. Four times larger.
b. 10 times larger.
c. 100 times larger.
d. 100,000 times larger.

(11) What is the temperature at the Sun's surface, approximately?
a. 300 K.
b. 6000 K.
c. One million K.
d. 15 million K.

(12) Which is the most abundant element in the Sun?
a. Hydrogen.
b. Helium.
c. Oxygen.
d. Nitrogen.

(13) What element is produced from hydrogen fusion in main sequence stars?
a. Helium.
b. Carbon.
c. Iron.
d. Plutonium.

(14) Can a star like the Sun become a supernova?
a. Yes, if we wait another 5 billion years.
b. Yes, if it is hit by a large asteroid.
c. No, it is not massive enough.
d. No, it has already been through that stage.

(15) What keeps white dwarfs from continuously shrinking to smaller sizes?
a. The resistance of electrons in them to being squeezed together.
b. The energy produced by nuclear reactions in their cores.
c. They are so cold that they become solid as opposed to gaseous.
d. The gravitational pull from other nearby stars.

(16) Is it correct to view a nova as a new star?
a. Yes, novas are explosions produced by the first nuclear reactions in a star.
b. Yes, novas are the collisions of dense clouds that produce newborn stars.
c. No, novas are just bursts of nuclear fusion on the surface of white dwarfs.
d. No, novas are flashes produced by stars disappearing down black holes.

(17) What can cause a supernova?
a. The formation of a bright young star out of interstellar matter.
b. The explosion at the end of a very massive star's life.
c. The formation of a new galaxy out of intergalactic matter.
d. The explosion at the end of a galaxy's life.

(18) Why does a star become red when it enters the giant/supergiant phase?
a. Because the stars's surface becomes even hotter than before.
b. Because its surface becomes colder from the expansion.
c. Because the star is surrounded by an obscuring nebula.
d. Because of the presence of heavy elements like iron.

(19) Where did we see a supernova in 1987?
a. In the crab nebula.
b. In the Andromeda galaxy.
c. Near the core of our galaxy.
d. In the Large Magellanic Cloud.

(20) For which stars can we find the distance using parallax?
a. The nearest ones, out to a few hundred light years.
b. The brighter ones, which can distinctly be seen.
c. The ones for which we can obtain a good spectrum.
d. All stars.

(21) Which of these could be the diameter of a neutron star?
a. 2 million light years.
b. 150,000,000 km.
c. 30,000 km.
d. 20 km.

(22) What would you expect to find at the center of an old planetary nebula?
a. A black hole.
b. A brown dwarf.
c. A white dwarf.
d. A giant planet.

(23) What is the event horizon?
a. The surface of a black hole, beyond which not even light can escape.
b. The farthest distance you would see if you were standing on a black hole.
c. The edge of a galaxy, beyond which there is only dark matter.
d. Another name for the first event in the universe, the big bang.

(24) Could you stand on the surface of a black hole?
a. No, there is no surface to stand on and you would just fall inward.
b. No, because black holes spin so fast they would fling you outward.
c. Yes, but you would never be able to leave the black hole's surface.
d. For a moment, but then you would be crushed by its strong gravity.

(25) Can light orbit a black hole?
a. No, light cannot orbit because it always moves in straight lines.
b. No, if light is bent by a black hole it will fall into it.
c. Yes, if it moves on the surface of the photon sphere.
d. Yes, if it stays exactly on the surface of the black hole.

(26) What would happen to you if you were to fall into a black hole?
a. You would be stretched and squeezed by strong tidal forces.
b. You would be crushed in all directions to a very small size.
c. You would feel colder and colder as you approach the hole.
d. You would be smashed by the impact with the black hole surface.

(27) Where are the most massive black holes located?
a. Inside thick dark nebulae.
b. Where the most massive stars in our galaxy used to be.
c. At the centers of our galaxy and other galaxies.
d. At the center of the universe.

(28) Which is the nearest star to us (other than the Sun)?
a. Sirius.
b. Betelgeuse.
c. Alpha Centauri.
d. Polaris.

(29) How far from us is the nearest star (other than the Sun)?
a. 400,000 miles.
b. 4 astronomical units.
c. 4 light years.
d. 40 million light years.

(30) What is the most common element in interstellar space?
a. Hydrogen.
b. Helium.
c. Carbon.
d. Oxygen.

(31) How can we find out the temperature of a star?
a. From the wavelength at which it emits most of its radiation.
b. From the amount by which its spectral lines are redshifted.
c. By comparing its apparent brightness and luminosity.
d. By measuring the rate at which its light flickers.

(32) What is a neutron star?
a. The remnant of a massive star after a supernova explosion.
b. A star that is too small to start burning hydrogen in its core.
c. The hottest, brightest kind of star on the main sequence.
d. A star in which all atoms are neutral instead of being ionized.

(33) Why are binary stars useful in astronomy?
a. Because they move more, so we can easily find their distance.
b. Because we can often find the masses of the stars involved.
c. Because they are brighter than a single star would be.
d. Because we can find the age of the two stars from their motion.

(34) What is a pulsar?
a. A rotating neutron star emitting a beam of radio waves.
b. A neutron star that pulsates by expanding and contracting.
c. A neutron star orbiting around a white dwarf and eclipsing it.
d. A Cepheid variable in the process of collapsing into a quasar.

(35) Why aren't stars eternal?
a. Because they are all moving and eventually are too far to be seen.
b. Because at the end they are all blown away by a violent explosion.
c. Because sooner or later they are all swallowed by a black hole.
d. Because they run out of fuel for the nuclear reactions that produce energy.

(36) What are the Pleiades?
a. Two stars in a very close, tight binary system.
b. The four stars at the center of the Orion nebula.
c. An open cluster of stars in Taurus.
d. A globular cluster of stars in Centaurus.

(37) Are there globular clusters in our galaxy?
a. Yes, there is one near the center of the galaxy.
b. Yes, we know almost 200 scattered in the halo of the galaxy.
c. Yes, there are hundreds of thousands of them in the galactic disk.
d. No, globular clusters are seen only in distant galaxies.

(38) For how long is a star like the Sun a main sequence star?
a. 10 billion years.
b. 150 million years.
c. 40 million years.
d. 4 million light years.

(39) Can we tell the size of a star from a picture taken with a good telescope?
a. No, image size for stars does not reflect actual size and we need more information.
b. Yes, large telescopes magnify images enough for us to see the sizes of most stars.
c. Yes, we can find the size from the brightness of the image on the photograph.
d. Yes, we can find the size from the color of the star's image on the photograph.

(40) The absolute magnitude of a star is a measure of
a. How large the star is, as determined from an actual photograph.
b. How large the star would appear to be, if it was where the Sun is.
c. How bright the star would be in the sky under perfect visibility conditions.
d. How bright the star would be if it was at a distance of 10 pc from us.

(41) After the Sun goes through its red giant phase, what will most of its outer layers and atmosphere become?
a. A planetary nebula.
b. A molecular cloud.
c. A post-stellar nebula.
d. A supernova remnant.

(42) In the Sun's convection zone, what is the main thing convection does?
a. It moves sunspots across the surface of the Sun.
b. It carries solar wind particles outwards into space.
c. It takes hot gas from the interior toward the Sun's surface.
d. It makes hydrogen atoms turn into helium atoms in the core.

(43) Which of the following things do you actually see when looking at an eclipsing binary star system?
a. A star from which the amount of light we receive changes in time.
b. A star for which the frequency of the spectral lines changes in time.
c. One whose visible spectrum shows both emission and absorption lines.
d. A two-star system in which both stars can be seen.

(44) Which of the following is a difference between an open cluster and a globular cluster?
a. Open clusters can contain hundreds of stars, globular clusters at most a few.
b. Open clusters can contain hundreds of stars, globular clusters hundreds of thousands.
c. Globular clusters are made of globules that are not stars yet, open clusters are made of stars.
d. Globular clusters are young and still round, open clusters are old and have started to break up.

(45) What do you need to know about a star to place it in the HR diagram?
a. Velocity and temperature.
b. Temperature and luminosity.
c. Luminosity and distance.
d. Distance and velocity.

(46) Have there been supernova explosions in our galaxy?
a. Yes, we see several of them every year.
b. Yes, but the last one was seen about 400 years ago.
c. Probably, but none has actually been observed by humans.
d. Not yet, so far we have seen them only in other galaxies.

(47) How can we find neutron stars?
a. If they are not surrounded by glowing matter there is no way for us to find them.
b. They can often be seen as pulsars, from which we get pulses of radio waves.
c. We recognize them because they shine more brightly than any other regular star.
d. We look for stars whose brightness changes over a period of a few days.

(48) Which of these is a possible cause for a supernova?
a. The formation of a bright young star out of interstellar matter.
b. The collapse of the core of a very massive star at the end of its life.
c. The formation of a new galaxy out of intergalactic matter.
d. The expansion of a small star to supergiant size at the end of its life.

Answers