ASTR 104 – Winter 2007 Intersession – Final Exam

Questions on material that we have not covered are greyed out. Blue questions refer to test 3 material.

(1) What do the stars that belong to a given constellation have in common?
-- They all belong to the same galaxy; stars in other constellations are in other galaxies.
-- They were all formed together; they have the same age and belong to the same star cluster.
-- They all have the same brightness and their spectra show the same absorption lines.
d. They just happen to be approximately in the same direction in space, as seen from Earth.

(2) In what do the Zodiac constellations differ from the others?
-- They are the ones that represent animals.
-- They are located along the celestial equator.
c. They are located along the Sun's path in the sky.
-- They are the ones in which the planets are located.

(3) Why is Sagittarius one of the most interesting constellations for astronomers?
-- Because it is one of the Zodiac constellations.
b. Because it is in the direction of the center of our galaxy.
-- Because it lies on the Celestial equator.
-- Because it contains the brightest stars in the sky.

(4) How does the Sun compare to the other stars in the sky?
-- The Sun is much brighter and bigger in size.
-- The Sun is the only yellow star, the others are all blue or red.
-- The Sun is the only one that has planets around it.
d. The Sun is a medium-small, normal-type star.

(5) Which is the brightest star in the night sky?
-- Betelgeuse.
-- Polaris.
c. Sirius.
-- Aldebaran.

(6) Which one of the currently recognized planets were known before telescopes were invented?
-- Only Venus and Mars.
-- Venus, Mars, Jupiter and Saturn.
c. Mercury, Venus, Mars, Jupiter and Saturn.
-- All eight of them.

(7) Can we see any galaxy (other than the Milky Way) with the naked eye?
-- No, the Milky Way is the only galaxy we have actually ever seen.
-- No, all other galaxies are way too distant and one needs a telescope.
c. Yes, M31 and the Magellanic Clouds can be seen as fuzzy objects.
-- Yes, a few thousands of galaxies can be seen in good viewing conditions.

(8) What is the celestial sphere?
a. An imaginary surface around the Earth used for locating stars and planets.
-- A sphere surrounding the Sun, on which the Earth and planets move.
-- The blue globe of the Earth, as it appears when viewed from space.
-- A sphere that separates the stars in our galaxy from other ones.

(9) Does any object rise in the West and set in the East at night?
-- Yes, some stars, called retrograde stars, do.
-- Yes, planets do when they are in retrograde motion.
-- No, celestial objects other than the Sun and Moon do not rise and set.
d. No, celestial objects always rise in the East and set in the West.

(10) Does the stars' position on the celestial sphere ever change over time?
-- No, stars can never move from their locations, only planets do.
b. Yes, because of the stars' motion in space, but only over many years.
-- Yes, because of the celestial sphere's rotation around its axis.
-- Yes, because of the Earth's rotation around its axis.

(11) When is a planet's motion called retrograde?
-- When it rotates backward around its axis.
b. When it drifts Westward on the celestial sphere.
-- When it is moving away from the Earth.
-- When it rises in the West and sets in the East.

(12) Which of the following is a reason why ancient astronomers believed in a geocentric model?
a. At that time, it was not possible to observe the stars' parallax.
-- The stars show a very obvious parallax displacement.
-- The retrograde motion of planets is best explained by geocentric models.
-- The geocentric model agreed with Copernicus' ideas.

(13) How did ancient geocentric models explain Mars' apparent retrograde motion?
a. Using the concept of epicyles.
-- Using the gravitational attraction of other planets.
-- They assumed it had been hit by an asteroid.
-- They assumed that its rotation axis was tilted.

(14) What is the main contribution to astronomy made by Copernicus?
-- He made excellent observations of the planets' positions.
b. He proposed a modern heliocentric model of the solar system.
-- He explained the orbits of planets in terms of gravity.
-- He was the first person to use a telescope in astronomy.

(15) Who is recognized as the first person to realize that the orbits of planets are ellipses rather than circles?
-- Ptolemy.
-- Copernicus.
-- Tycho Brahe.
d. Kepler.

(16) How are ellipses related to the orbits of planets?
-- The planet is at one focus, the Sun at the other one.
b. The Sun is at one focus, the planet moves along the ellipse.
-- The Sun is at the center, the planet moves along the ellipse.
-- The planet and the Sun are at opposite points of the ellipse.

(17) How do heliocentric models explain the apparent retrograde motion of Mars?
-- Using the concept of epicycles.
-- Using the gravitational attraction of other planets.
c. From the fact that the Earth and Mars orbit the Sun at different speeds.
-- From the fact that the measurements it was based on were wrong.

(18) As a planet revolves around the Sun, does the Sun also feel a pull and move?
-- No, because in this case the Sun is the center of attraction.
b. Yes, the Sun feels the same pull but it is so massive that it hardly moves.
-- Yes, the Sun feels the same pull and moves as much as the planet does.
-- Maybe, but there is no way for us to find out because the Earth itself is moving.

(19) What is parallax used for in astronomy today?
-- To align the axis of a telescope with the Earth's rotation.
-- To locate the point representing a star on an HR diagram.
c. To find the distance to a star from its apparent displacement.
-- To determine whether and how fast they Earth is moving.

(20) If star A appears larger than star B in a photograph, you conclude that
-- Star A is larger in size than star B.
-- Star A is closer to us than star B.
c. Star A appears brighter than star B, as seen from Earth.
-- Star A is younger than star B.

(21) Which is hotter, a supergiant star or a main sequence star?
-- The supergiant star.
-- The main sequence star.
-- They have the same temperature.
d. We would need to know their spectral type to answer.

(22) What kind of star is Rigel?
-- A main sequence star.
-- A red supergiant.
c. A blue supergiant.
-- A white dwarf.

(23) Is it common for two stars to orbit around each other?
-- No, stars do not orbit around each other, only planets orbit around stars.
-- No, only about 2% of stars are sufficiently close to each other.
c. Yes, possibly about half of all stars are that close to each other.
-- Yes, all stars revolve around one or more other stars.

(24) What is an open cluster?
-- A group of similar stars that is spread over more than one constellation.
b. A small group of stars, usually young, blue and bright, in our galaxy's disk.
-- A large group of many thousands of stars, usually old, in our galaxy's halo.
-- A globular cluster which has been torn apart by a collision with another one.

(25) Are there globular clusters in our galaxy?
-- Yes, there is one near the center of the galaxy.
b. Yes, we know about 180 scattered in the halo of the galaxy.
-- Yes, there are hundreds of thousands of them in the galactic disk.
-- No, globular clusters are seen only in distant galaxies.

(26) What causes the collapse of an interstellar cloud that leads to star formation?
a. Gravity.
-- Heat.
-- Rotation.
-- Magnetic fields.

(27) Why are there no stars with less than 8% of the sun's mass?
-- Because they have evolved past the stage where we can see them.
b. Because such would-be stars are not hot enough to fuse hydrogen.
-- Because they have not had time to reach the main sequence yet.
-- We don't know; such stars may exist, but we have not seen any.

(28) For how long is a star like the Sun a main sequence star?
a. 10 billion years.
-- 150 million years.
-- 40 million years.
-- 4 million light years.

(29) What does convection have to do with how a stars works?
-- It makes dark spots move across the surface of the star.
-- It pushes the stellar wind from the surface out into space.
c. It takes energy from deep inside the star to the surface.
-- It makes hydrogen atoms turn into helium atoms in the core.

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

(31) Which of the following objects do we expect the Sun to become at some point in the future?
-- Neutron star.
-- Supernova.
-- Black hole.
d. White dwarf.

(32) When did the last supernova explosion happen inside our galaxy?
-- We don't know of any supernova explosions in our own galaxy.
-- 5 billion years ago, right before the Solar System formed.
c. About 400 years ago.
-- Last year .

(33) What is the biggest mass a neutron star can have?
-- 1.4 solar masses.
b. 3 solar masses.
-- 100 solar masses.
-- There is no maximum neutron star mass.

(34) What is the biggest mass a black hole can have?
-- 1.4 solar masses.
-- 3 solar masses.
-- 100 solar masses.
d. There is no maximum black hole mass.

(35) What is the best thing to look for, when trying to find a black hole?
-- A region of space which is totally black, with no background stars shining through.
-- A place where all gas and dust has been sucked away by its gravitational force.
c. A disk of hot matter, whose radiation indicates a massive small object at the center.
-- There is no way to ever see them, black holes remain purely theoretical objects.

(36) Have gravitational waves been detected?
-- Yes, this is the reason Einstein received the Nobel prize.
-- Yes, the announcement was made by NASA last month.
c. No, but detectors are operational and are expected to find them.
-- No, they cannot be detected directly because they are ficticious waves.

(37) What effect does dust in interstellar clouds have on starlight?
a. It dims and reddens the light.
-- It bends and focuses the light.
-- It causes light to be blueshifted.
-- It absorbs light at some specific wavelengths.

(38) If an interstellar nebula looks blue, what can you conclude about it?
-- The light it emits has been blueshifted.
-- The hydrogen atoms in it emit mostly blue light.
-- The red light they emit has been scattered away.
d. The nebula reflects mostly blue light from nearby stars.

(39) What are Messier objects, the ones whose name is "M" followed by a number?
-- Very large dust grains in interstellar space; the number indicates their size.
-- Bright comets; the number indicates the length of their tails.
c. Fuzzy objects such as star clusters, nebulae, and galaxies (but not comets).
-- Objects that have not yet been identified and given an actual name.

(40) Where does 21-cm radiation come from?
a. Electrons inside hydrogen atoms, whose spin direction changes.
-- Oxygen molecules in interstellar space.
-- Nuclear reactions inside the cores of stars.
-- The surface of very hot, blue supergiant stars.

(41) What kind of galaxy are we located in?
-- We are not inside a galaxy.
b. Spiral.
-- Elliptical.
-- Irregular.

(42) What are the Magellanic Clouds?
-- Large clouds of gas and dust near the center of the Milky Way.
-- Smaller clouds of dust near the Trapezium inside the Orion nebula.
c. Two small irregular galaxies orbiting around the Milky Way.
-- The two largest galaxies in the Local Group.

(43) How can we find the distance to a nearby galaxy, like Andromeda?
-- We use the parallax method.
-- We find its temperature and use the HR diagram.
c. We look for variable stars such as Cepheids in it.
-- We find its velocity and use Hubble's law.

(44) What is a normal value for the distance between neighboring galaxies?
-- A few thousand light years.
-- Hundreds of thousands of astronomical units.
b. A few millions of light years.
-- A few billions of light years.

(45) What is the Virgo Cluster?
a. The nearest large cluster of galaxies to us.
-- A globular cluster of stars in the Andromeda galaxy.
-- A open cluster of stars inside the Milky Way.
-- The small cluster of galaxies that we belong to.

(46) How do we know that most galaxies are moving away from us?
a. The light we receive from them is redshifted.
-- The light we receive from them is very faint.
-- Over many years, we see them becoming smaller.
-- From the fact that many of them bump into each other.

(47) What is cosmology?
-- The study of the solar system.
-- The study of how stars form and evolve.
-- The study of the galaxy.
d. The study of the evolution of the whole universe.

(48) Why do we believe that the universe is expanding?
a. Because all distant galaxies appear to be moving away from us.
-- Because of the spiral shape of many galaxies.
-- Because the sizes of many galaxies seem to be increasing.
-- Because we were closer to the Andromeda galaxy in the past.

(49) Where is the center of the universe?
-- At the center of the Milky Way.
-- Near the middle of the Virgo cluster of galaxies.
-- We don't know exactly, but somewhere near the Great Attractor.
d. There is no center, if our current ideas are correct.

(50) According to our current understanding, how old is the universe?
-- About 2 million years.
-- About 250 million years.
c. About 13.7 billion years.
-- It has always existed.

(51) What is Olbers' paradox?
a. The fact that the night sky is dark rather than bright.
-- The fact that the universe is still expanding after so long.
-- The fact that there is so much dark matter in the universe.
-- The fact that such a large universe could have come from a point.

(52) If the universe is infinite in size, how come beyond a certain distance we stop seeing galaxies?
-- Beyond that distance all galaxies become too faint.
-- Beyond that distance there is just empty space with no more galaxies.
-- There are too many clouds of gas and dust in between.
d. We are looking back in time to when galaxies first started forming.

(53) If we watch galaxies for a long time, do we see them change?
-- Yes, but we must watch them for a few years at least.
-- Yes, but only the nearby ones like the Andromeda galaxy.
c. No, changes take hundreds of millions of years, way too long.
-- No, galaxies never change, only stars inside them move and evolve.

(54) Do galaxies collide?
-- No, they are way too far apart to collide with each other.
-- We have not seen any collisions yet, but it could possibly happen.
c. Yes, we have seen many examples of distant galaxies colliding.
-- Yes, in fact we are now colliding with the Andromeda galaxy.

(55) Can we see young galaxies?
-- Yes, newborn galaxies are being formed right now in our own neighborhood.
b. Yes, we see the most distant galaxies the way they were billions of years ago.
-- No, all galaxies formed billions of years ago and we can no longer see young ones.
-- We don't know, we can't tell a galaxy's age because they don't appear to change.

(56) How do active galaxies differ from normal ones?
-- Their brightness may change over a period of a few hours.
b. They are brighter and emit a lot more radio waves and infrared.
-- Their shape is irregular, as opposed to elliptical or spiral.
-- They move faster across the sky if we watch them for a few years.

(57) What is ultimately responsible for the fact that a galaxy is more active than others?
-- Nuclear reactions, burning hydrogen into helium in the core.
b. Matter falling into a supermassive black hole at the center.
-- Dark matter heating up the gas and dust in the disk.
-- Supernova explosions throughout the galaxy.

(58) What are quasars?
-- Clouds of matter that are about to collapse and form stars.
-- Very old galaxies that are about to explode at the end of their lives.
-- Stars that managed to escape from a galaxy and float freely in space.
d. Young, very active galaxies that are so far away they look like red stars.

(59) What is dark matter?
-- The matter out of which black holes are made.
-- Matter whose gravity repels rather than attracting.
-- Clouds of dust responsible for the fact that the sky is dark at night.
d. Matter that we detect only by its gravitational pull on other objects.

(60) What can we find out by measuring how fast different stars move around the galactic center?
-- How old the Milky Way is.
b. How much mass there is in the galaxy.
-- How fast the universe is expanding.
-- Whether those stars will fall onto the central black hole.

(61) Which of the following is the correct order of formation of matter in the universe, starting from the earliest?
a. Particles, nuclei, atoms, molecules.
-- Nuclei, particles, molecules, atoms.
-- Atoms, particles, nuclei, molecules.
-- Molecules, atoms, particles, nuclei.

(62) What is the evidence for dark matter in galaxy clusters?
-- The X-rays we get from the space between galaxies.
-- The speed at which galaxies move around the center.
-- The lensing of distant images produced by the cluster.
d. All of the above.

(63) What are WIMPS?
a. Subatomic particles that are thought to be part of the dark matter.
-- Dwarf, slow-moving stars that are thought to be part of the dark matter.
-- Small, slow-moving clouds of dust that obscure part of the Milky Way.
-- Astronomers who are opposed to funding for new, larger telescopes.

(64) What is the difference between dark matter and dark energy?
a. Dark matter tends to slow down the expansion of the universe, dark energy speeds it up.
-- Dark matter is matter that fell into a black hole, dark energy travels at the speed of light.
-- Dark matter absorbs all types of light, dark energy only specific wavelengths.
-- Nothing, they are two expressions for the same concept.

(65) According to current ideas, what is the universe composed of?
-- 95% regular matter, 5% dark matter.
-- 10% regular matter, 90% dark energy.
-- 5% regular matter, 5% dark energy, 90% dark matter.
d. 5% regular matter, 25% dark matter, 70% dark energy.

(66) How long after the Big Bang did neutral atoms form?
-- One second.
-- Three minutes.
c. 300,000 years.
-- One billion years.

(67) What evidence do we have that the universe started with a hot big bang?
a. The cosmic microwave background.
-- The presence of dark matter.
-- The age of globular clusters in our galaxy.
-- The fact that the cores of many galaxies are still burning.

(68) What kind of radiation fills the universe and is considered to be evidence for the Big Bang?
-- Dark energy.
b. The cosmic microwave background.
-- 21-cm radio waves.
-- The universal X-ray background.

(69) When were all the nuclei of atoms in the universe that are not just hydrogen produced?
-- They all originated in the first few minutes after the big bang.
-- They were all produced later in nuclear reactions inside stars.
-- Inside the supermassive black holes in the cores of galaxies.
d. Many of them in the early universe, the rest later inside stars.

(70) Where did the cosmic microwave radiation come from?
-- The explosion of the first generation of massive star supernovas.
b. All the radiation produced by particles before atoms formed in the hot early universe.
-- Charged particles moving in the intense magnetic fields of some black holes.
-- All the nebulas in all the galaxies we see today in the universe combined.