ASTRONOMY 161 Introduction to Solar System Astronomy

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ASTRONOMY 161Introduction to Solar System
Astronomy
Class 27
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A161 Class Review
Friday, December 4
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A161 Final Exam

• Astronomy 161 -- Autumn 2009 (Prof. Stanek)
• Final Exam Monday, December 7, 1130 a.m.
• There will be 100 questions on the Final Exam.
• Final will count for 40 of the final grade.
• Please bring your OSU picture ID.

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Top 10 Things I Want You to Remember Forever

• 10 The acceleration of an object is directly
  proportional to force, and inversely proportional
  to mass (Newtons Second Law of Motion).

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Newtons Second Law of Motion

• The acceleration of an object is directly
  proportional to the force acting on it, and
  inversely proportional to its mass.
• In mathematical form
• Or alternatively

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10 Things I Want You to Remember Forever

• 9 Lunar phases change as we see more or less
  of the Moon's sunlit half.

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The Moon is a sphere illuminated by the Sun.

• Half closest to Sun is light.
• Half furthest from Sun is dark.

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10 Things I Want You to Remember Forever

• 8 Light can be though of as a wave or as a
  particle.

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Speed of light

• Speed of wave, c, equals wavelength times
  frequency (units meter/sec)
• c l x n
• The speed of light in a vacuum is always
• c 300,000 km/s
• (186,000 miles/sec).

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Photons

• The energy of a photon is related to the
  frequency of a wave
• E hn
• E energy of photon
• n frequency of light
• h Plancks constant (A Small Number)

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10 Things I Want You to Remember Forever

• 7 Copernicus proposed a heliocentric model for
  the universe. In the model of Copernicus,
  retrograde motion of planets is easily explained.

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As Earth laps Mars, Mars appears to go backward
as seen by observer on Earth.

• 1 2 3 prograde (forward)
• 4 5 6 retrograde
• 7 8 9 prograde again

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10 Things I Want You to Remember Forever

• 6 Newtons Law of Gravity
• The gravitational force between masses M and m,
  separated by distance r, is
• FG(Mm/r2)

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Newtons Law of Gravity

• The gravitational force between two objects
• F gravitational force
• M mass of one object
• m mass of the second object
• r distance between centers of objects
• G universal constant of gravitation

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10 Things I Want You to Remember Forever

• 5 A lunar eclipse occurs when the Moon passes
  through the Earth's shadow. A solar eclipse
  occurs when the Earth passes through the Moon's
  shadow.

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The shadow of the Earth (or any other object) has
two parts

• Umbra inner part of shadow, Sun completely
  hidden.
• Penumbra outer part of shadow, Sun partially
  hidden.

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A lunar eclipse occurs when the Moon passes
through the Earths shadow.

• Lunar eclipses occur when Earth is between Sun
  and Moon.
• Lunar eclipses occur at FULL MOON.

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• Solar eclipses occur when Moon
  is between Sun and Earth.
• Solar eclipses occur at NEW MOON.

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10 Things I Want You to Remember Forever

• 4 Radioactive age-dating indicates the Solar
  System is 4.56 billion years old.

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Radioactive age-dating

• Radioactive decay Unstable atomic nuclei emit
  elementary particles, forming a lighter, stable
  nucleus.
• Example Potassium-40 (19 protons 21 neutrons
  40)
• 89 of the time, Potassium-40 decays to
  Calcium-40.
• 11 of the time, Potassium-40 decays to Argon-40.

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• Age of oldest Earth rocks 4 billion years
• Age of oldest Moon rocks 4.5 billion years
• Age of oldest meteorites (meteoroids that survive
  the plunge to Earth) 4.56 billion years
• This is the age of the Solar System!
• (agrees well with our understanding of the age of
  the Sun)

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10 Things I Want You to Remember Forever

• 3 Normal matter in the Universe (including
  our Sun) is mostly hydrogen and helium. The
  terrestrial planets are made primarily of rock
  and metal. The Jovian planets are made primarily
  of hydrogen and helium.

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• Abundance of elements
  in the Suns atmosphere
• Hydrogen (H) 75
• Helium (He) 23
• Everything else 2
• As discovered in 1920s, other stars are mostly
  hydrogen and helium, too.

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The terrestrial planets are
made primarily of rock and metal.

• Mercury, Venus, Earth, Mars.
• The terrestrial planets are
  low in mass (lt Earth mass) high
  in density (gt 3900 kg/m3).
• Water 1000 kg/m3
• Air 1 kg/m3
• Rock 3000 kg/m3

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The Jovian planets are
made primarily of hydrogen and helium.

• Jupiter, Saturn, Uranus, Neptune
• The Jovian planets are
• high in mass (gt 14 Earth masses)
• low in density (lt 1700 kg/m3).
• Jovian planets are made mainly of light elements
  like hydrogen and helium.

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10 Things I Want You to Remember Forever

• 2 Many extrasolar planetary systems found so
  far are very different from the Solar System.

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Many planetary systems are very different from
the Solar System.

• MAJOR SURPRISE!
• Often we see high-mass planets very close to the
  central star (closer than Mercury is to the Sun).
• According to the nebular theory, massive
  planets should form far from the star, where it
  is cool enough.

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Top 10 Things I Want You to Remember Forever

• 1 The cause of the seasons is the tilt of the
  Earth's rotation axis relative to its orbit
  around the Sun.

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What causes the Earths seasons?

• The tilt of the Earths rotation axis relative to
  the Earths orbit around the Sun.

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Two reasons why summer is warmer than winter

• 1) Sun is above the horizon longer during the
  summer
• 2) Sun rises higher in sky during the summer.

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Final Exam Sample Questions

• Which of the following has the largest diameter?
  
• A) the largest asteroid
  
• B) the nucleus of Halleys Comet
  
  
• C) the largest satellite of Mars
  
• D) Pluto
  
• E) the largest crater on Jupiter

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Final Exam Sample Questions

• On the first day of winter the sun rises
• A) Due South
• B) South of East
• C) Due East
• D) North of East
• E) Due West

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Final Exam Sample Questions

• In order of distance from Jupiter, the Galilean
  moons are Io, Europa, Ganymede, and Callisto.
  Craters cover all of Callisto, but only 1/3 of
  Ganymede. A probable conclusion is
  
  
• A) Our view of Ganymede is blocked by Jupiters
  rings
  
• B) Ganymede had more tectonic activity because it
  is larger
  
• C) Ganymedes craters were obliterated by heat
  from Jupiter
  
• D) Ganymede suffered a giant impact with Europa
  
  
• E) All of the other answers are correct

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Final Exam Sample Questions

• The masses of planets are measured from
  
• A) their brightness.
  
• B) their size and density.
  
• C) acceleration their gravity produces on nearby
  objects.
  
• D) infrared and radio emission.
  
• E) their resistance to being gravitationally
  accelerated.

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Final Exam Sample Questions

• If you could observe Earth through a telescope
  from Mars, Earth would
• A) always be in gibbous or full phase
• B) always be in crescent phase
• C) go through all phases from crescent to full
• D) have largest apparent diameter when in full
  phase
• E) appear at full phase when seen at opposition

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Final Exam Sample Questions

• Why are fewer craters found on the Earth than on
  the Moon?
  
• A) The Earth is protected by its magnetic field
  
  
• B) Tides on the Moon are stronger than on Earth
  
  
• C) Earths gravity is stronger, so it has fewer
  impacts
  
• D) The Moon has many more volcanoes
• E) Earths craters have been destroyed

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Final Exam Sample Questions

• The complete list of planets known to have rings
  is?
  
• A) Saturn
  
• B) Saturn and Uranus
  
• C) Saturn, Jupiter, Uranus, and Neptune
  
  
• D) Saturn and Jupiter
  
• E) Saturn, Uranus and Neptune

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Final Exam Sample Questions

• Titan has an atmosphere, liquids, ices, and rain
  made of
  
• A) ammonia
  
• B) methane
  
• C) water
  
• D) carbon dioxide
  
• E) hydrogen

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Final Exam Sample Questions

• What does the Earth have that no Jovian planet
  has?
  
• A) A rotation period less than 30 hours
  
• B) Hurricanes
  
• C) A density similar to that of water
  
• D) Impact craters
  
• E) An atmosphere

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Final Exam Sample Questions

• The process which makes the Moon move gradually
  away from the Earth is similar to the one which
• A) generates Jupiters magnetic field
• B) gives rise to 60 of giant impacts
• C) produces sunspots
• D) supplies energy for the volcanoes on Io
• E) Actually, the Moon is not moving away from
  Earth

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Final Exam Sample Questions

• Where is the full moon just after sunset?
• A) Near the Western horizon
• B) Nearly overhead
• C) Close to the North star
• D) Close to the South star
• E) Near the Eastern horizon

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Final Exam Sample Questions

• Name the planet which comes closest to the Earth
  (26 million miles)
  
• A) Saturn
  
• B) Jupiter
  
• C) Venus
  
• D) Uranus
  
• E) Mercury

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Final Exam Sample Questions

• All other things being equal, a planet with
  higher albedo would be _____ compared to a planet
  of lower albedo.
  
• A) hotter
  
• B) cooler
  
• C) at the same temperature
  
• D) less boring

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This is our last lecture!