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Astronomy 12
Astronomer:
KEY
Final Exam Review
Part I- Multiple choice: Answer each question by shading the most appropriate bubble.
01. Astronomy is the study of
a. the stars and planets and their movements as well as their affects on the lives and behavior of
human beings.
b. the weather and of atmospheric processes.
c. the structure and evolution of the earth's crust.
d. everything in the universe that lies above Earth's atmosphere.
02. Which of the following terms would not be associated with astronomy?
a. horoscope
b. telescope
c. astrolabe
d. celestial sphere
03. A planet is an object which
a. occurs only in our solar system.
b. is too faint to see.
c. orbits a star.
d. does not generate its own energy from nuclear reactions
04. In astronomical terms, one brief description of a star is
a. a small point of light seen only at night.
b. a radiant body at least 3 million times as massive as the Earth.
c. a bright object with a five-pointed shape.
d. a body which shines from its own internal source of energy.
05. A galaxy is
a. a large cloud of gas.
b. an exploding star.
c. the object from which all other objects in the universe were formed.
d. a collection of a large number of stars bound by gravity.
06. A(n) _____ is the totality of all space, time, matter, and energy.
a. universe
b. galaxy
c. planet
d. star
07. Which of the following is arranged from the smallest to the largest in size?
a. planet, star, universe, galaxy
b. star, planet, galaxy, universe
c. planet, star, galaxy, universe
d. universe, galaxy, star, planet
08. What are constellations?
a. galaxies of stars
b. configurations of bright stars patterned by humans
c. areas of the sky, each 15 x 15 degrees
d. physical groupings of stars all at the same distance from Earth
09. The picture below shows Orion’s Belt.
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Orion’s Belt
Orion’s Belt is an example of a(n)
a. constellation.
b. asterism.
c. star cluster.
d. galaxy.
10. Which of the following terms is correct?
a. The Big Dipper is an asterism in the constellation Ursa Major.
b. Ursa Major is an asterism in the constellation of the Big Dipper.
c. Both the Big Dipper and Ursa Major are constellations.
d. Both the Big Dipper and Ursa Major are asterisms.
11. A band of the celestial sphere extending on either side of the ecliptic that represents the path of
the different celestial bodies (i.e. Moon, Sun, planets) and contains constellations like Gemini and
Aquarius is called the
a. North Celestial Pole.
b. South Celestial Pole.
c. Celestial Equator.
d. Zodiac.
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12. An imaginary sphere of infinite extent with Earth at its center on which the stars, planets, and
other heavenly bodies appear to be located is known as the
a. Zodiac.
b. celestial sphere.
c. atmosphere.
d. Valhalla.
13. Which one of the following statements is true about the celestial coordinates known as "right
ascension" and "declination"?
a. They change from one day to the next due to the Earth's rotation.
b. They are measured with respect to the observer's local zenith and horizon.
c. They are fixed in space with respect to Earth's axis and the Sun's direction at the vernal equinox.
d. They were used by the ancient Greeks to determine the size of the Sun.
14. FILL IN THE BLANKS: Declination is analogous to geographical ______________. Right
ascension is analogous to geographical ______________.
a. latitude; longitude
b. longitude; latitude
c. north pole; south pole
d. south pole; north pole
15. The time needed for a star on the celestial sphere to make one complete rotation in the sky is
referred to as a
a. sidereal month.
b. solar year.
c. sidereal day.
d. solar day.
16. The period of time between the instant when the Sun is directly overhead to the next time it is
directly overhead is referred to as a
a. sidereal month.
b. solar year.
c. sidereal day.
d. solar day.
17. Relative to the stars on the celestial sphere, over the course of a year, the ecliptic is the
apparent path of what celestial body?
a. Moon
b. Sun
c. Alpha Centauri
d. Earth
18. The Sun rises in the east and sets in the west because
a. the Earth rotates on its axis.
b. the Earth revolves around the Sun.
c. the Moon revolves around the Earth.
d. the Earth ‘wobbles’ on its axis.
19. The point on the ecliptic where the Sun is at its northernmost point above the celestial equator,
occurring on or near June 21, is known as
a. winter solstice.
b. vernal equinox.
c. summer solstice.
d. autumnal equinox.
20. The point on the ecliptic where the Sun is at its southernmost point below the celestial equator,
occurring on or near December 21, is known as
a. winter solstice.
b. vernal equinox.
c. summer solstice.
d. autumnal equinox.
21. The date on which the Sun crosses the celestial equator moving southward, occurring on or
near September 22 is known as
a. winter solstice.
b. vernal equinox.
c. summer solstice.
d. autumnal equinox.
22. The date on which the Sun crosses the celestial equator moving northward, occurring on or
near March 21.
a. winter solstice.
b. vernal equinox.
c. summer solstice.
d. autumnal equinox.
23. The time required for the constellations to complete once cycle around the sky and return to
their starting points, as seen from a given point on Earth, is referred to as a
a. synodic month.
b. sidereal month.
c. tropical year.
d. sidereal year.
24. The time interval between one vernal equinox and the next is referred to as a
a. synodic month.
b. sidereal month.
c. tropical year.
d. sidereal year.
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25. The slow but relatively uniform motion of the earth's rotational axis that causes changes in the
coordinate systems used for mapping the sky is known as
a. penumbra.
b. parallax.
c. precession.
d. phase.
26. The appearance of the sunlit face of the Moon at different points along its orbit, as seen from
Earth, is referred to as a
a. parallax.
b. phase.
c. lunar eclipse.
d. solar eclipse.
27. A _____ eclipse occurs whenever the Moon passes through some portion of the Earth's
shadow.
a. solar
b. lunar
c. total
d. partial
28. A _____ eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring
Earth's view of the Sun.
a. solar
b. lunar
c. total
d. partial
29. The darkest part of the shadow is called the
a. penumbra.
b. umbra.
c. baseline.
d. dark zone.
30. The part of a shadow where the light source is only partially blocked is called the
a. penumbra.
b. umbra.
c. baseline.
d. light zone.
31. The difference in position of a star as seen from the Earth at different locations around the orbit
of the Sun is known as
a. triangulation.
b. transit.
c. stellar parallax.
d. precession.
32. During its orbital period, as a planet moves closer to the Sun, the orbital velocity of the planet
___.
(a) increases
(b) decreases
(c) remains the same
33. According to Newton’s law of universal gravitation, the force of attraction between any two
masses is directly related to the ___.
(a) distance between the masses
(b) product of the two masses
(c) velocity of the two masses
(d) sum of the two masses
34. According to Kepler, planetary orbits are _________ in shape.
a. elliptical b. circular c. spiral d. wavy
35. What are the four Terrestrial Planets?
(a) Charon, Earth, Uranus, Mars
(b) Mars, Venus, Mercury, Earth
(c) Venus, Pluto, Mercury, Jupiter
(d) Neptune, Uranus, Sol, Jupiter
35. What are the four Jovian Planets?
(a) Saturn, Neptune, Jupiter, Uranus
(b) Mars, Ceres, Mercury, Saturn
(c) Uranus, Mercury, Mars, Neptune
(d) Charon, Neptune, Uranus, Mars
36. What is another name for an interstellar gas cloud?
(a) Nebula
(b) Coma
(c) Corona
(d) Solar wind
37. What solar system object revolves around the Sun, has enough gravity to form a nearly round
shape, and have no other objects of similar size in it’s orbit?
(a) Planet
(b) Comet
(c) Meteoroid
(d) Asteroid
38. Which of the following set of conditions are most likely to result in a magnetic field in a planet?
(a) Liquid and electrically-conducting material in its interior and rapid rotation.
(b) Closeness to Sun.
(c) Iron core and slow rotation.
(d) Solid surface containing iron and slow rotation.
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39. The age of the solar system has been measured by radioactive dating. Which of the following
objects gives the most precise value for this age?
(a) the oldest rocks from the Moon
(b) the oldest rocks on the Earth
(c) the oldest meteorites
(d) the rocks in Mr. Jennings’ head
40. What method has been used in the successful search for planets around stars other than the
Sun?
(a) Hubble Space Telescope photography of faint, nearby companions of stars
(b) detection of the spectral signature of methane gas near the star, since this gas is known to be a
major constituent of the atmospheres of major planets
(c) measurement of the "wobble" of a star, caused by the orbital motion of the planet, detected
either by accurate positional measurement of the star or by spectral Doppler shifts in the stars
spectrum
(d) detection of the bending of light due to strong gravitational fields between Earth and the star
system.
41. What happens when an object gains more matter through its gravitational pull.
(a) Accumulation (b) Accretion (c) Evaporation (d) Outgassing
42. What is the outward flow of charged particles from the sun called?
(a) Out gassing
(b) Nova
(c) Evaporation (d) Solar wind
43. What is a planet that revolves around a star, other than our sun?
(a) protoplanet (b) planetesimal (c) extrasolar planet (d) exotroid
44. Using Bode’s Law for planetary orbital radii, what is the next number in the sequence of
numbers:
0.4, 0.7, 1.0, 1.6, 2.8, ____
(a) 10.0 (b) 5.2 (c) 4.8 (d) 4.4
45. Light has a particle nature, and these particles are called photons. Which region of the
electromagnetic spectrum has the highest energy photons?
(a) gamma ray
(b) ultraviolet
(c) visible
(d) infrared
46. A source of light moves toward you. According to the Doppler effect
(a) the frequency of the light will increase.
(b) the frequency of the light will decrease.
(c) the wavelength of the light will increase.
(d) the velocity of the light will increase.
47. The spectral classification of a star is closely related to the star’s
(a) brightness.
(b) luminosity.
(c) surface temperature.
(d) distance.
48. How does the H-R diagram help astronomers identify stars?
(a) It plots a star’s mass and core temperature, which allows astronomers determine the
colour and region of where star is formed.
(b) It plots a star’s luminosity and spectrum, which allows astronomers determine the size of
the star.
(c) It plots a star’s luminosity and surface temperature, which allows astronomers determine
the type of star, size of star, and the star’s stage of evolution.
(d) It plots a star’s size and surface temperature, which allows astronomers determine its
region of origin.
49. What is the Main Sequence?
(a) The evolutionary path, as seen on the H-R diagram, that a star follows throughout
its life.
(b) The region on the H-R diagram where, once they are formed. new stars rest for most of
their lives.
(c) The sequence of events a star follows from its formation to supernova.
(d) The region on the H-R diagram where protostars first appear.
50. Define hydrogen burning.
(a) The formation of a hydrogen gas cloud, also known as a nebula.
(b) The chemical combustion of hydrogen.
(c) the separation of the hydrogen envelope to form a planetary nebula.
(d) The formation of helium by fusing hydrogen together.
51. When a star’s gravitational force pulling inwards and its internal pressure pushing outward are
balanced, it is considered to be in what?
(a) Hydrostatic equilibrium
(b) Supernova
(c) Structural Balance
(d) Proton-proton fusion
52. What is a helium flash?
(a) The rapid fusion of helium in a red giant’s core.
(b) An explosion that creates a planetary nebula.
(c) A type of solar flares that occurs on the surface of sun-type stars.
(d) A flash of white light that occurs when a star collapses into a white dwarf.
53. What is a planetary nebula?
(a) The destroyed remains of a planetary solar system when a sun-type star expands
to a red giant.
(b) The ejected envelope of a red giant that was formed from a sun-type star.
(c) The disk of material around a protostar that will eventually form planetary system.
(d) The initial massive gas cloud that stars and planets are formed from.
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54. A white dwarf found in a binary system suddenly brightens, settles back down in a few months,
and has the possibility to repeat. What is this called?
(a) Red Giant
(b) Carbon-detonation supernova (Type One)
(c) Planetary nebula
(d) Core collapsing supernova (Type Two)
55. High-mass protostars evolve into main-sequence stars
(a) more quickly than low-mass protostars because their stronger gravity speeds up their collapse.
(b) more quickly than low-mass protostars because their higher core temperature speeds up their
collapse.
(c) more slowly than low-mass protostars because their stronger gravity slows their collapse.
(d)s more slowly than low-mass protostars because their higher core temperature slows their
collapse.
56. In which of the following types of galaxies would you be least likely to find a newly-formed star?
a) Elliptical
b) Spiral
c) Irregular
Use the diagram below to answer the next 3 questions:
57. Region #1 is referred to as the galactic _____.
a) halo
b) disk
c) bulge
d) cluster
58. Region #2 is referred to as the galactic _____.
a) halo
b) disk
c) bulge
d) cluster
59. Region #3 is referred to as the galactic _____.
a) halo
b) disk
c) bulge
d) cluster
60. What does Hubble’s law tell us about how galaxies are moving?
a) All galaxies are moving away from us at the same velocity.
b) Galaxies close to us are receding from us slowly, and galaxies farther from us are receding
more rapidly.
c) Galaxies close to us are receding from us rapidly, and galaxies farther from us are receding
more slowly.
d) Galaxies have random distribution of velocities—there is no pattern.
61. The cosmic microwave background radiation is
a) all of the radiation currently existing in the universe produced by all possible sources.
b) all of the radiation emitted by stars since the first stars were born.
c) leftover radiation from the original Big Bang that has been tremendously redshifted by the
expansion of the universe.
d) radio emission from various radioactive galaxies.
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Part II- Short Answer: Answer each question on the test paper in the space provided.
49. Label the various parts of the celestial sphere below:
A Celestial Equator
B Ecliptic
C North Celestial Pole
D South Celestial Pole
E Earth
50. Explain how right ascension and declination are used to locate objects in the sky.
-start at the vernal equinox
-move eastward through 0 to 24 hours (analogous to moving through different geographical longitude lines)
-move north (+) or south (-) through 0 to 90 degrees to the object’s location (analogous to moving through
different geographical latitude lines)
51. The solar day is 3.9 minutes longer than the sidereal day. Why is this so?
-solar day takes into account the Earth’s revolution around the Sun during its rotation on its axis and is therefore
longer.
52. Why does Earth experience seasons? Be sure to mention Earth’s rotational axis and the Sun’s energy in your answer.
Astronomy 12 Test – Final Exam Review KEY
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As seen in the diagram above, during the winter season, the Northern Hemisphere is tilted away from the Sun and
receives less direct sunlight. This means that the atmospheric temperature does not rise as much as in summer.
During the summer season, the Northern Hemisphere is tilted towards the Sun and receives more direct sunlight.
This means that the atmospheric temperature rises more than in the winter.
53. The sidereal year is about 20 minutes longer than the tropical year.
a. Why is this so?
The sidereal year is the time for the Earth to revolve around the Sun relative to the stars, while the tropical
year is the time for the Earth to revolve around the Sun relative to the vernal equinox. These two years are
slightly different because precession causes the vernal equinox to move relative to the stars.
b. If modern calendars were based on the sidereal year, what would be the effect on timekeeping?
The calendar is based on the tropical year so that the first day of spring occurs approximately on the
same date each year. If the calendar was based on the sidereal year, eventually important dates like
Easter and Christmas would be at different dates throughout the year.
54. Label the phases of the Moon. Indicate phase name below its image.
New Moon
Waxing
Crescent
1st Quarter
Waxing
Gibbous
Full Moon
Waning
Gibbous
3rd Quarter
Waning
Crescent
55. One sidereal month is 27.3 days. One synodic month is 29.5 days. Explain this difference.
The sidereal month is the time that the Moon takes to go around the Earth once relative to the stars. The synodic
month is the time that the Moon takes to go around the Earth relative to the Sun. The synodic month is longer by
about 2.3 days. During the sidereal month the Sun appears to move about 27 o due to the Earth’s orbital motion. It
takes the extra 2.3 days for the Moon to catch up to the Sun.
56. Draw a diagram that would illustrate a lunar eclipse.
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57. Draw a diagram that would illustrate a solar eclipse. Indicate the regions on Earth’s surface where total and partial
eclipses would be seen.
58. Explain how astronomers use triangulation to find stellar distances. You can use the astronomical unit calculation activity
as an example.
This is stellar parallax. Parallax involves measuring the distances to nearby stars, whose display an apparent
shift in position against background stars observed as Earth moves along its orbit.
59. How does the Earth’s axial tilt of 23.5o determine why is it hotter in the summer and colder in the winter in the Northern
Hemisphere?
{see answer to #52}
60. Recall the night-time observation assignment that required you to locate the approximate location of the North Celestial
Pole in the sky. If you were a student in Astronomy 12 in the year 15 000 C.E., how would this task be different?
The task would be different due to precession, which shifts the NCP from Polaris to Vega in 12 000 years (i.e. 2012
C.E. + 12 000 years = 15 000 C.E.).
61. Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the
Earth and the Moon; the Sun also exerts a gravitational attraction on the Earth but to a lesser degree. The gravitational
attraction causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since
the Earth is also being pulled toward the moon (and away from the water on the far side). Since the earth is rotating while
this is happening, two tides occur each day. Spring tides are especially strong tides (they do not have anything to do with
the season Spring). Neap tides are especially weak tides. Given all these points, draw diagrams of that illustrate the
difference between spring and neap tides.
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62. Construct a Venn Diagram comparing and contrasting the geocentric and heliocentric models of the universe.
Geocentric
Universe
-Earth-centered with
Sun, Moon, planets
revolving around Earth
-required deferent for
main orbital path and
epicycle to account for
retrograde motion
-could not explain stellar
parallax
Heliocentric
Universe
-both described
geometry of Solar
System
-both attempted to
explain retrograde
motion
-Sun-centered with
Earth, Moon, planets
revolving around Sun
-no epicycle required
(i.e. retrograde motion
explained by planets
revolving at various
speeds)
-could explain stellar
parallax
63. Draw a label a diagram that illustrates the geocentric model of the solar system. Be sure to include the following parts:
deferent, epicycle, planet, Earth, Sun.
64. Define perihelion and aphelion.
Perihelion is the point on the orbital path of a planet closest to the Sun; aphelion is the point on the orbital path of
a planet farthest from the Sun.
65. State Kepler’s 3 Laws of Planetary Motion.
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1st: the orbit of a planet about the Sun is an ellipse with the Sun at one focus
2nd: a line joining a planet and Sun sweeps out equal areas in equal time intervals (i.e. a planet travels
fastest at the perihelion and slowest at aphelion)
3rd: the period of a planet’s orbit squared (in years) is equal to the orbital radius of the planet cubed (in
AU) (i.e. P2 = a3)
66. State Newton’s Law of Universal Gravitation.
The gravitational attractive force between two objects (i.e. a planet and the Sun) is directly related to the product
of the mass of the two objects and inversely related to the square of the distance between them.
67. State Newton’s three laws of motion.
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First law: The velocity of a body remains constant unless the body is acted upon by an external force.
Second law: The acceleration a of a body is parallel and directly proportional to the net force F and
inversely proportional to the mass m, i.e., F = m x a.
Third law: For every action, there is a reaction force, equal in magnitude (i.e. size) but opposite in
direction
68. The orbital distance from Saturn to the Sun is approximately 10.0 A.U. Using Kepler’s 3 rd Law of Planetary Motion (P2 =
a3), what is the period of Saturn (or the time it takes Saturn to revolve around the Sun)?
P2 = a3  P = √(10.0 AU)2 = 31.6 years
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69. It takes Mars 688 days to revolve around the Sun. What is its orbital distance from the Sun?
Convert 688 days to years….688/365 = 1.88 years
P2 = a3  a = cube root [(1.88 years)2] = 1.52 AU
70. State Newton’s revisions to Kepler’s Laws of Planetary Motion.
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1st law: Newton agreed with Kepler but said that orbits could be elliptical if bound and the planet would
continue to orbit regularly. Orbits could be parabolic or hyperbolic if unbound (i.e. planet passes Sun
once and leaves Solar System)
2nd law: Newton said that the change in velocity or acceleration of a planet around the Sun is due to
gravity
3rd law: Newton agreed that P2/a3 ratio was true for all planets in Solar System but was able to use gravity
to determine the mass of Sun
71. State Bode’s Law. Compare its usefulness and accuracy to Kepler’s 3rd Law of Planetary Motion.
Bode’s law is a pattern of numbers that predict the orbital distances (in AU) from the Sun to all the planets with
reasonable accuracy:
0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 19.6, 38.8
It is useful for approximate distances but only useful for planets and not other Solar System objects. Kepler’s 3 rd
law can be used to find orbital distances of any Solar System object.
72. Use Bode’s Law to predict the orbital radius of the Asteroid Belt.
At 2.8 AU in the Bode’s law pattern, a planet was predicted to exist. After careful searching, astronomers
determined that at this distance, the Asteroid Belt resides and not a planet.
73. Using Newton’s law of gravitation, if the distance between a planet and the Sun increases by a factor of 4, how does the
force of gravity between the planet and Sun change?
The force of gravity would decrease by a factor of 16 (i.e. 42 = 16).
74. List Newton’s laws of motion and an example for each.
{see answer to #67; examples will vary}
75. List the major types of structures in the solar system, from the largest to the smallest mass.
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Sun, planets, moons, asteroids, comets
76. Why is Pluto no longer considered a planet?
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It has a highly eccentric orbit (eccentricity = 0.25).
It is a very rocky object.
Numerous trans-Neptunian objects the size of Pluto have been discovered.
77. Explain how the planets in our solar system were formed.
6 Steps to Form a Solar System
THE NEBULAR HYPOTHESIS
1. Solar Nebula Forms
 A huge cloud of cold gas and dust.
 Many times larger than our present solar system.
 Probably spinning very slowly.
2. Formation of the Protosun
 Under the influence of gravity, the solar nebula
condensed into a dense central region (the protosun)
and a diffuse outer region (the protoplanetary disk).
 Began to spin faster, flattened out, and central region
heated up.
3. Rings and Planetesimals
 Instabilities in the rotating disk caused regions within it
to condense into rings under the influence of gravity.
 Gradually, planetismals formed in these rings.
4. Terrestrial or Rocky Planets
 The planetismals attracted each other by gravity and collided to build planets.
 Closest to the protosun, only rocky material and metals could withstand the heat, and so the planets in
this region are made mainly of these materials.
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5. Jovian or Gas Giants
 In the outer part of the disk, the bodies formed from planetesimals made of rock and ice.
 They became big enough to attract large amounts of gas around them.
 Soon after these gas planets formed the protosun became a full-fledged star.
6. Remaining Debris
 Radiation from the Sun blew away most of the remaining gas and other material in the planetary solar
system.
 Some of the leftover planetismals in the outer part of the disk formed the Kuiper Belt and Oort cloud of
comets.
78. Describe the difference between how terrestrial and jovian planets
were formed. Use diagrams, if needed.
For jovian planets, initially core formed by accretion of solid
materials and then, gas accreted onto solid core to form gas giant
(i.e. core accretion model). Alternatively, gases rapidly accrete
and condense to form Jovian planets without a solid core due to
denser areas in the protoplanetary disk (i.e. disk instability
model).
79. A star is has a parallax of 0.02 arcseconds. How far away is this star? SHOW ALL WORK & CALCULATIONS
Use d = 1/p  d = 1/(0.02’’) = 50 parsecs
80. Describe the methods by which extrasolar planets are detected.
Transit Method
If a planet crosses (or transits) in front of its parent star's disk, then the observed
visual brightness of the star drops a small amount. The amount the star dims
depends on the relative sizes of the star and the planet.
Astrometry
This method consists of precisely measuring a star's position in the sky and observing
how that position changes over time. If the star has a planet, then the gravitational
influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit.
If the star is large enough, a ‘wobble’ will be detected.
Doppler Shift (Radial Velocity)
A star with a planet will move in its own small orbit in response to the planet's gravity. The
goal now is to measure variations in the speed with which the star moves toward or away
from Earth. In other words, the variations are in the radial velocity of the star with respect to
Earth. The radial velocity can be deduced from the displacement in the parent star's spectral
lines (think ROYGBIV) due to the Doppler effect.
Pulsar Timing
A pulsar is a neutron star: the small, ultra-dense remnant of a star that has exploded as a
supernova. Pulsars emit radio waves extremely regularly as they rotate. Because the rotation
of a pulsar is so regular, slight changes in the timing of its observed radio pulses can be used
to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it
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has a planet. Calculations based on pulse-timing observations can then reveal the geometry of that orbit
Gravitational Microlensing
The gravitational field of a star acts like a lens, magnifying the light of a
distant background star. This effect occurs only when the two stars are
almost exactly aligned. If the foreground lensing star has a planet, then that
planet's own gravitational field can make a detectable contribution to the
lensing effect.
Direct Imaging
Planets are extremely faint light sources compared to stars and what little light comes from
them tends to be lost in the glare from their parent star. It is very difficult to detect them
directly. In certain cases, however, current telescopes may be capable of directly imaging
planets.
81. A star has a surface temperature of 10 000 K. What is the peak wavelength (in meters) of light emitted from the surface?
SHOW ALL WORK & CALCULATIONS
Use Wein’s Law max = (0.0029 Km)/T = (0.0029)/(10000 K) = 0.00000029 m = 290 nm (blue light)
82. Describe at least three properties of a star that an astronomer can deduce from its spectrum.
(1) chemical composition, from the presence of the characteristic spectral lines of certain elements;
(2) temperature, from spectral type;
(3) star’s speed toward or away from us, from Doppler shift of the lines;
(4) density, axial rotation, and surface magnetic fields, from line shape and width.
83. If a red star and a blue star have the same radius and brightness, which one is farther from Earth? Explain why.
Because the stars have the same radius, the lower-temperature red star (using Wein’s law) must be nearer (using
Stefan-Boltzmann law) in order to have the same apparent brightness as the higher-temperature blue star.
84. If a red star and a blue star have both appear equally bright and both are the same distance from Earth, which one has the
larger radius? Explain why.
Because the stars are the same brightness and distance from Earth, the lower-temperature star (using Wein’s
law) red star must be larger (using Stefan-Boltzmann law) in order to have the same brightness as the highertemperature blue star.
85. Complete tree diagram below: describe the two types of supernovas.
Supernova
Type I – Carbon
Detonation
-lack H lines in spectra
-can be formed from WD in binary
system or supergiants with H/He
removed
-found everywhere in Galaxy
-produced from old, low-mass stars
-fixed maximum brightness
Type II – Core
Collapsing
-have H lines in spectra
-formed from young, massive stars
-observed in arms of spiral galaxies
-end result: NS or BH
-stay brighter longer, with variable
maximum brightness  brightness
decreases rapidly
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77. Complete table below: For each STAGE, write the letter of its STAGE DESCRIPTION in the corresponding blank. See #7
as an example.
H-R Diagram
Stage
(7 to 14)
Stage Description
7. ___F___
A.
B.
C.
D.
8. ___I___
9. ___C___
10. ___D___
11. ___L___
12. ___B___
E.
F.
G.
H.
I.
13. ___M___
14. ___A___
J.
K.
L.
M.
Black Dwarf
Planetary Nebula
Helium Flash
Carbon core expands
and star returns to a
balance state.
Supernova
New Star
Oxygen fusion
Carbon burning
Forms a helium core
as it leaves the main
sequence
Protostar
Fragmentation
Carbon core contracts
and star climbs Giant
branch again.
White dwarf
78. Explain the general formation of a sun-type star (i.e. Steps 1-6).






Stage 1: Fragmentation of Nebula  with sufficient mass, nebula fragments repeatedly under gravity
Stage 2: Fragmentation Stops  lower-mass fragments form until internal gas pressure greater than gravity
and fragmentation stops; thin fragment with hot center
Stage 3: Formation of a Protostar  protostar and protoplanetary disk form; heat and light from gravitational
energy at the core produce YSO (no fusion)
Stage 4: Can be Seen on H-R diagram  no fusion but gravitational collapse produces sufficient surface
temperature and luminosity to be measured on H-R diagram
Stage 5: Violent Surface Activity  due to increasing core pressure from gravity, core traps heat that is
released from time to time, causing violent surface activity
Stage 6: Helium Core is Formed  core temperature sufficient to produce proton-proton fusion and helium
deposited in core
79. Complete the Venn diagram to the right in order to compare the history of high mass stars with low mass stars (Hint: think
the formation, evolution and death of the different stars).
80. A star has a mass of 8.5 solar masses. Predict what will happen to this star when it leaves the Main Sequence on the HR
Diagram.
When this star leaves Main Sequence, because of its high mass, it will become a blue supergiant, undergoing
heavy element burning. This produces iron in the stellar core. Once all fusion processes cease, the star core
contracts rapidly producing a supernova explosion. The core remnant from this event is a neutron star, a
densely-packed core of neutrons (produced from compacted protons and electrons), with a strong magnetic field.
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(note: if the original star were about 10 solar masses or greater, the supernova remnant would have been a black
hole).
81. Using the Hubble Classification of Galaxies below, classify the four galaxies.
Sb
Irr
E5 (or S0)
SBb
82. Explain why Hubble’s Classification System cannot be used as an evolutionary path of galaxies.
 If Hubble’s classification system could be used as an evolutionary path of galaxies, then elliptical galaxies
would eventually form into spiral galaxies. This means that spiral galaxies should only contain very old stars
 Since spiral galaxies contain both young and old stars, they cannot have formed from elliptical galaxies
83. Describe the dark-matter problem. How is dark matter detected in the Universe?
 The dark matter problem is the mystery that most of the matter in the Universe seems not to emit radiation of
any kind and is detectable by gravity alone.
 Dark matter is indirectly detected by its gravitational effects on ‘regular matter’, including galaxy rotation and
gravitational lensing.
84. How is the formation of spiral and elliptical galaxies related to the initial rate of star formation in the protogalactic nebulae
from which they were formed?
 The initial rate of star formation in elliptical galaxies is thought to be much greater than that of spiral galaxies
 The increased amount of time for initial star formation allowed spiral galaxies to form as they did
85. The Universe is considered to be both homogenous and isotropic. Explain the difference between these terms.
 On large scales, the Universe is homogenous, which means that there are similar properties in every region.
 “Isotropic” means that the Universe is the same in all directions (i.e. there is no preferred location in the
Universe in which to measure the Universe).
86. Using Hubble’s Law (v = H0 x d), find the velocity of a galaxy that is 100 Mpc from the Milky Way Galaxy.
(Note: H0 = 74.3 km/s/Mpc)
v = H0 x d = (74.3 km/s/Mpc)(100 Mpc) = 7430 km/s
therefore, galaxies that are 100 Mpc away in any direction are moving away from the Milky Way at 7430 km/s
87. Describe four pieces of evidence that suggest that the Big Bang is the best model for describing the formation of the
universe.
 Redshift of light from distant galaxies  Hubble law of expansion
 The presence and temperature of cosmic microwave background radiation (CMBR)
 Evolved structures, e.g. galactic clusters, galaxies, stars
 Abundance of lighter elements, e.g. H and He, in the Universe (1st elements to be produced after initial Big
Bang)
88. Contrast three possible fates of the Universe in the future. Relate each fate to the Universe’s critical density. Which fate
do cosmologists feel is most likely to occur?
 Open: Universe expands at an accelerating rate; density is less than critical density (Big Rip)
 Closed: Universe’s expansion slows and halts and collapses under gravity; density is greater than critical
density (Big Crunch)
 Flat: Universe expands at a constant rate of acceleration, without ripping apart or crunching; density is equal
to critical density
 Cosmologists feel that the Universe is flat and will expand forever. They think this due to data collected from
COBE and WMAP missions.
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