Astronomy 161:
Introduction to Solar System Astronomy
Autumn 2003

Syllabus & Reading Assignments

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Textbook:

W. J. Kaufmann III,		Universe
R. A. Freedman		(7th Edition)

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Discovering Earth and Sky

Week 1 (September 22-24) :

• Lecture 1 (September 22): What is Science? What is Astronomy?
  • Assigned Reading:
    • Chapter 1: Sections 1, 2, 6, 8.
  • Summary:
    • Science must describe natural phenomena in the universe based on rational, mathematical reasoning. Quantitative explanations are subject to test by experiment and observation.
    • Astronomy is about every object or event we observe on the sky.
  • Key Questions:
    • What are the conditions for any body of knowledge to be science?
    • What part of science is astronomy?
    • Why does science oppose authority?

• Lecture 2 (September 23): The Celestial Sphere: Stars, Angles on the Sky, Daily Motion.
  • Assigned Reading:
    • Sections 1.5, 2.1, 2.2, 2.3.
  • Summary:
    • The celestial sphere is the map of angular positions of all stars on an imaginary sphere around the Earth. It tells us the direction to each star, but it does not tell the distance.
    • Separations between stars or sizes of objects on the sky are measured in angles.
    • The North Celestial Pole is the projection of the North Pole onto the celestial sphere. The celestial Equator is the projection of the Earth's equator onto the celestial sphere.
    • The rotation of the Earth causes the apparent daily motion of the stars.
  • Key Questions:
    • How do stars move on the sky relative to the horizon of an observer on Earth?
    • Why do they move that way?
    • How is the separation between two stars on the celestial sphere measured?
    • What is the zenith?
    • What is the North Celestial Pole?

• Lecture 3 (September 24): Apparent Motion of the Sun. The Seasons. Sidereal day.
  • Assigned Reading:
    • Section 2.5, Box 2.2
  • Summary:
    • The seasons are caused by the tilt of the axis of the Earth. Winter: days are shorter and the Sun is lower over the horizon.
    • The Sun is seen to move over the sky in one year relative to the stars. This is why we see different stars at night at different seasons.
    • The Earth spins 366.25 times in a year relative to the distant stars. The sidereal day is one spin relative to the distant stars. The solar day is the time between two successive passes of the Sun across the Meridian, and is slightly longer than the sidereal day.
  • Key Questions:
    • What is the reason for the seasons?
    • Why do we see different stars at night in the different seasons?
    • What time of the year does the Sun reach its maximum height over the horizon in South Africa?
    • How many times does the Earth spin around its own axis during a year?

Week 2 (September 27 - October 1) :

• Lecture 4 (September 27): Measuring the Earth: the Eratosthenes Method.
  • Assigned Reading:
    • Section 1.5, Box 1.1, Section 3.6.
  • Summary:
    • Eratosthenes measured the latitude difference between two cities by noticing the maximum height the Sun reached in each city. With the small-angle formula he derived the size of the Earth.
    • We use the small-angle formula to derive the size of an object once we know its angular size and its distance.
    • The latitude determines the angular height above the horizon at which we see the North Celestial Pole.
  • Key Questions:
    • If the North Pole star is on the zenith, where are you on the Earth?
    • If the Sun reaches the zenith exactly on the Summer solstice, what is your latitude?
    • How did Eratosthenes calculate the size of the Earth?
    • If we know the angular size of an object seen on the sky, what else do we need to know its real size?

• Lecture 5 (September 28): The Celestial Sphere and Celestial Coordinates. Precession.
  • Assigned Reading:
    • Sections 2.4 and 2.6, Box 2.1.
  • Summary:
    • Star positions are specified by two coordinates, declination and right ascension.
    • Declination is the angle from the celestial equator to the star.
    • Right ascension is the angle that a great circle fixed on the poles needs to rotate to go from the Vernal equinox to the star.
    • The Earth axis precesses once every 26000 years, due to the tides from the Moon and the Sun. This causes the precession of the equinoxes.
  • Key Questions:
    • What coordinates do we use to specify the position of a star?
    • What is the declination of a star on the celestial equator?
    • What is the declination of a star that is halfway between the celestial equator and the South pole?
    • Has the star Polaris always been close to the North pole?
    • What causes precession of the equinoxes?

• Lecture 6 (September 29): Phases of the Moon.
  • Assigned Reading:
    • Sections 3.1, 3.2, Box 3.1
  • Summary:
    • The phases of the Moon are caused by its orbit around the Earth and the illumination by the Sun.
    • Last quarter Moon is seen during the second half of the night and in the morning.
    • We always see the same face of the Moon because it rotates once per orbit, being locked up to the Earth.
    • The Moon takes 27.32 days to orbit the Earth. The period of phases, or synodic period, is a little longer.
  • Key Questions:
    • What time of the day and night can we see the First Quarter Moon?
    • How long does it take for the Moon to move around the sky once relative to the stars? Is this the same as the time between two Full Moons?
    • Why do we always see the same face of the Moon?
    • When the Moon is Full, what time does it rise and set, and what time is it near the Meridian?

• Lecture 7 (September 30): Eclipses of the Sun and the Moon.
  • Assigned Reading:
    • Sections 3.3, 3.4, 3.5.
  • Summary:
    • Lunar eclipses occur when the Moon is Full and is shadowed by the Earth. They can be total, partial, or penumbral.
    • Solar eclipses occur when the New Moon covers the Sun. They can be partial, total, or annular, and they are different from different locations on Earth.
    • Eclipses occur only when the Sun-Earth line is close to the line of nodes of the Moon's orbit.
  • Key Questions:
    • Why isn't there a lunar eclipse at every Full Moon and a solar eclipse at every New Moon?
    • Does a lunar eclipse look the same from everywhere on Earth? How about a solar eclipse?
    • Why can there be total and annular solar eclipses?
    • What is a penumbral lunar eclipse?

• Lecture 8 (October 1): Measuring the Size and Distance of the Sun and the Moon.
  • Assigned Reading:
    • Sections 1.5, 1.6, 3.6, Box 1.2
  • Summary:
    • The diurnal parallax is the change in the direction to an object on the sky from two different locations on Earth.
    • The Moon's distance can be measured by the effect of the diurnal parallax. It was measured also by Aristarchus from the size of the Earth umbra in a lunar eclipse and the known size of the Earth.
    • The Sun is 400 times further than the Moon and its radius is 100 times that of the Earth.
  • Key Questions:
    • What is the effect of diurnal parallax?
    • What can we measure from the diurnal parallax of the Moon?
    • What does the fact that the time of the First Quarter Moon is almost exactly between New Moon and Full Moon imply?
    • What do total lunar eclipses imply about the relative size of the Earth and the Moon?

Gravity and the Rise of Modern Astronomy

Week 3 (October 4-8) :

• Lecture 9 (October 4): Motions of Planets on the Sky.
  • Homework 1 handed out.
  • Assigned Reading:
    • Sections 4.1, 4.2.
  • Summary:
    • Interior planets are always seen close to the Sun, they reach a maximum eastern and western elongation from the Sun.
    • Interior planets are at superior conjunction when they are behind the Sun, and inferior conjunction when they are in front of the Sun.
    • Exterior planets are at conjunction when they are behind the Sun, and at opposition when they are opposed to the Sun. They show retrograde motion when they are in opposition.
  • Key Questions:
    • If you see Venus in the evening, will its next conjunction be inferior or superior?
    • Can you ever see Mercury next to the Full Moon?
    • During what part of the day and night can you see Jupiter when it is in opposition?
    • When does Mars look faintest?
    • Does Saturn show retrograde motion?

• Lecture 10 (October 5): The Geocentric and the Heliocentric Model.
  • Homework 1 due.
  • Assigned Reading:
    • Sections 4.1, 4.2, 4.3.
  • Summary:
    • The geocentric model accounted for planet motions based on many epicycles. It did not explain why interior planets follow the Sun and retrograde motions aoccurs at opposition.
    • Copernicus showed that heliocentric model gave a natural explanation of planet motions. He computed orbit sizes and sidereal periods for all the planets.
    • Galileo used the phases of Venus to disproof Ptolemy's model.
  • Key Questions:
    • What were the tools used by the geocentric model to explain planet motion?
    • How does the geocentric model explain that retrograde motion always takes place at opposition? How does the heliocentric model explain that?
    • What is the phase of Venus at superior conjunction? How does that contradict the geocentric model?
    • Did Copernicus have to use epicycles?

• Lecture 11 (October 6): Kepler's Laws of Planetary Motion.
  • Assigned Reading:
    • Section 4.4, 4.5
  • Summary:
    • Kepler found his three laws by trial and error, trying to adjust Tycho's observations of planet positions.
    • Planets move around the Sun on elliptical orbits, and the Sun is at one focus.
    • A line joining the planet with the Sun sweeps out equal areas in equal intervals of time.
    • The square of the sidereal period is proportional to the cube of the semimajor axis.
  • Key Questions:
    • How did Kepler figure out his three laws of planetary motion?
    • At what point does a planet move slower? Is this point on the major or the minor axis?
    • If a planet moving around the Sun has an orbit of 10 Astronomical Units, what is its period in years?
    • If a planet moving around the Sun has a period of 2 years, what is the semimajor axis of its orbit?

• Lecture 12 (October 7): Galileo's Discoveries
  • Assigned Reading:
    • Sections 4.3, Box 1.3
  • Summary:
    • Galileo's discoveries with the telescope: mountains on the Moon, phases of Venus, sunspots, Jupiter's satellites, Milky Way made of many stars.
    • Galileo also worked on the laws of motion. He understood that in the absence of forces, objects will continue moving with a constant velocity along a straight line. He figured out that gravity on the Earth's surface makes all objects fall with the same acceleration, and that the trajectory of falling objects is a parabola.
    • Galileo followed the scientific method and defended the heliocentric model. But he was also still prejudiced and obstinate on certain things: he believed planets must move on circular orbits.
  • Key Questions:
    • What did Galileo find out about the Moon, Venus, Jupiter, and the Sun?
    • Why was Galileo the first to know about all this?
    • How did this influence his views on the heliocentric model?
    • Did Galileo relate his principle of inertia to the motions of the planets?

• Lecture 13 (October 8): Newton's Laws
  • Assigned Reading:
    • Section 4.6, Box 4.3.
  • Summary:
    • Newton formulated three laws that govern all motion. Learn the three laws!
    • First Newton's law: A body remains at rest, or moves in a straight line at constant speed, unless acted upon by a net outside force.
    • Second Newton's law: The net outside force that must act on a body that accelerates is equal to its mass times its acceleration.
    • Third Newton's law: Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body, which we call the reaction to the first force.
  • Key Questions:
    • If you are at rest and not accelerating, does this imply that no force may be applied on you?
    • If we could turn off the force of gravity at some instant of time, what would all the planets do?
    • If a big boulder and a leaf fall down in a room where we have made a vacuum, which one is subject to the greatest acceleration? Which one is subject to the greatest force?
    • The Sun exerts a force on the Earth that keeps it on its orbit. Which is the reaction to that force?

Week 4 (October 11-15) :

• Lecture 14 (October 11): Newton's Law of Gravity and the Motion of the Moon.
  • Assigned Reading:
    • Section 4.7
  • Summary:
    • The law of universal gravitation: any two objects, whatever their nature or composition, attract each other with a force proportional to the product of the masses and inversely proportional to the distance squared.
    • Earth's force of gravity is responsible for the fall of objects on Earth's surface and for the orbit of the Moon.
  • Key Questions:
    • What is the force that makes the Moon go around the Earth?
    • If you stand next to a big truck, why don't you feel the gravitational attraction towards it?
    • If you move out to space to a distance from the center of the Earth equal to twice its radius, how much smaller will the gravitational acceleration be compared to the value at the surface?
    • What will happen if you put two rocks in space at rest close to each other? Will they remain at rest?

• Lecture 15 (October 12): Newton's Explanation of Planetary Motion.
  • Assigned Reading:
    • Section 4-7.
  • Summary:
    • Newton proved that his three laws of motion and the law of universal gravitation imply that a body moving under the gravitational force of another body must move over a trajectory that is a circle, an ellipse, a parabola or a hyperbola, obeying all of Kepler's laws.
  • Key Questions:
    • What are the possible trajectories that an object moving under the gravity of another object can follow?
    • Why do we feel the gravity of the Earth but not the gravity of the Sun?
    • Do comets obey Kepler's laws?
    • If a spacecraft is sent to Mars and it passes by it without using its jet engines, subject only to the force of gravity, what is the shape of its trajectory around Mars?

• Lecture 16 (October 13): How we Know the Mass of the Sun, the Earth, and the Planets.
  • Assigned Reading:
    • Section 4.7, Box 4.4, review boxes 1.2 and 1.3.
  • Summary:
    • Newton's generalization of the third Kepler's law allows one to measure the mass of any object with a satellite moving around it.
    • The planets also attract each other, causing perturbations on their orbits. The perturbations from Kepler's laws were observed to be precisely as predicted.
    • Binary stars were also found to orbit around each other following Kepler's laws.
  • Key Questions:
    • How do we know the mass of the Sun?
    • How do we know the mass of Jupiter?
    • Do planets in the Solar System obey Kepler's laws exactly, or only approximately?
    • Venus has no satellites. How do we know its mass?

• Lecture 17 (October 14): More Triumphs of Newton's Laws: Tides and Neptune's Discovery.
  • Assigned Reading:
    • Sections 4.8, 16.1. Box 9-1.
  • Summary:
    • Newton's theory of gravity makes many successful, quantitative predictions. Planetary perturbations were so accurately tested that the presence of a new planet was required and its position predicted, leading to the discovery of Neptune in 1846.
    • Other successful predictions: the tides due to the Moon and the Sun, the oblateness of the Earth, the period of precession of the equinoxes.
  • Key Questions:
    • How were Uranus and Neptune discovered?
    • What causes ocean tides?
    • If the Earth rotated slower, how would its shape change?
    • What causes precession of the Earth's axis?

Light the Messenger: the Rise of Astrophysics.

• Lecture 18 (October 15): What is light?
  • Assigned Reading:
    • Sections 5.1, 5.2.
  • Summary :
    • Light carries energy and brings us information from astronomical objects.
    • Light has a fixed speed c=300000 km/s.
    • Light has a wavelength with a broad spectrum, and is also called electromagnetic waves or radiation.
    • Frequency is the speed divided by the wavelength.
    • Objects in the universe emit radiation at all kinds of frequencies.
  • Key Questions:
    • What does the finite speed of light imply about what we observe in the universe?
    • How does the wavelength of X-rays compare to that of visual light?
    • Which has the longest wavelength, red light or blue light? Roughly by what factor is it larger or smaller?
    • Since radio waves at 100 MHz have a frequency 5 million times smaller than waves of visual light, how are the wavelengths of these two waves related?

Week 5 (0ctober 18-22) :

• Lecture 19 (October 18): Blackbody Radiation.
  • Homework 2 handed out.
  • Assigned Reading:
    • Section 5-3, Box 5-1.
  • Summary :
    • All objects emit radiation, the more the hotter they are.
    • Objects that absorb all radiation incident upon them are called blackbodies and must emit the full blackbody spectrum, which depends only on their temperature.
    • Opaque objects are often well approximated by blackbodies even though in practice no material is a perfect blackbody (they all reflect some light).
  • Key Questions:
    • A hot rock is inside a cold box in space, the rock does not touch the box and there is no air around the rock. Will the box get hot because of the rock it contains?
    • What is the spectrum of the light emitted by an object?
    • If we turn off all the lights in a room, what kind of radiation will still be present? What objects will look brightest?

• Lecture 20 (October 19): The Stefan-Boltzmann and Wien Laws.
  • Homework 2 due.
  • Assigned Reading:
    • Section 5-4, Box 5-2.
  • Summary :
    • Wien's law: the wavelength at which the intensity of blackbody radiation is maximum is inversely proportional to temperature.
    • Stefan-Boltzmann law: the power per unit area is proportional to the temperature to the fourth.
    • For a sphere of radius R: total power or luminosity = 4*pi*R^2*sigma*T^4.
  • Key Questions:
    • When an object is at a temperature of 0 F, is it emitting radiation?
    • If a blackbody is at temperature 290 K, is all the radiation emitted at the wavelength lmax = 0.0029/T = 10 micrometers?
    • If a blackbody gets twice as hot, how much will the wavelength of the maximum power change?
    • If a blackbody gets twice as hot, how much will the total power emitted change?

• Lecture 21 (October 20): Atoms and Ions and their Spectral Signatures.
  • Assigned Reading:
    • Sections 5-5, 5-7. Boxes 5-3, 5-5.
  • Summary :
    • Atoms are made of a nucleus and electrons. The nucleus contains most of the mass but is very small compared to the electron orbits.
    • Electrons can occupy certain states with a discrete set of energies, and can jump from one state to the other.
    • Light is made of photons with energy E=h*nu
    • An atom can only emit or absorb photons with the energy needed to jump from one state to another.
  • Key Questions:
    • If an atom has atomic number 7, what does that tell us about the particles it contains?
    • What is the difference between an atom and an ion?
    • Which photon has the most energy, a yellow photon or a green photon? A red photon or an ultraviolet photon? An infrared photon or a radio photon?
    • How does light interact with a single atom or molecule?

• Lecture 22 (October 21): Atomic Spectral Lines and Kirchhoff's Laws.
  • Assigned Reading:
    • Sections 5-6, 5-8.
  • Summary :
    • Every atom and molecule has a special signature in its spectrum, which allows its identification in astronomical objects, such as stars, gas clouds, and planet atmospheres.
    • First Kirchhoff law: A hot, opaque object emits a continuous spectrum.
    • Second Kirchhoff law: A hot, transparent gas produces an emission line spectrum.
    • Third Kirchhoff law: A cool, transparent gas in front of a source of continuous radiation produces an absorption line spectrum.
  • Key Questions:
    • When we look at a hot solid object, what kind of a spectrum do we see?
    • If air is heated to very high temperature, what kind of a spectrum will it emit?
    • How could Kirchhoff prove that other stars are made of the same atomic elements that we know about?

• Lecture 23 (October 22): Telescopes.
  • Assigned Reading:
    • Chapter 6, all sections.
  • Special website:
    • Check out The Large Binocular Telescope , being built in Mount Graham in Arizona, to which the Ohio State University is a partner.
  • Summary:
    • Refracting telescopes work with lenses, and reflecting ones with mirrors with a shape that focuses the light rays.
    • Large telescopes collect more light and increase the image resolution. Atmospheric turbulence puts a limit to the resolution of large optical telescopes.
    • The development of sensitive electronic cameras and spectrographs has allowed taking images and spectra of much fainter objects than it was possible with photographic plates in the past.
    • Telescopes in space can take images with much better resolution, in the absence of the blurring from the atmosphere. They can also detect radiation at wavelengths at which it is blocked by the atmosphere.
    • Radio telescopes can be used on the ground and they are big reflecting dishes with radio receivers at the focus.
  • Key Questions:
    • Why is the size of a telescope related to its observing power?
    • Why are today's visual telescopes reflecting? Why are they built in high mountains?
    • Why is it useful to have telescopes in space?
    • How is the light behind the telescope detected in present observatories?

Week 6 (October 25-29) :

• October 25: Review day

• October 26: MIDTERM I EXAM , Lectures 1 to 22.

• Lecture 24 (October 27): How Far is the Sun?
  • Assigned Reading:
    • Review Section 3-6.
  • Optional Reading:
    • Professor Pogge wrote an excellent account of the adventures of many explorers who travelled far in 1761 and 1769 to measure the time of the Venus transits. Read Prof. Pogge's lecture notes
  • Summary:
    • Aristarchus first found the Sun is very far and must be much bigger than the Earth.
    • Copernicus measured the relative sizes of planet orbits but did not know the absolute distance from the Earth to the Sun.
    • Diurnal parallax was used to measure the Astronomical Unit, and Venus transits in 1761-1769 and 1874-1882 allowed the greatest accuracy of this measurement.
    • Today we know distances very accurately from radar.
  • Key Questions:
    • How did Copernicus measure the relative distance of the Earth and Venus to the Sun? How did he measure the absolute distance from the Earth to the Sun?
    • What is the method that astronomers used in the 18th century to measure the distance to the Sun? Why were Venus transits particularly relevant for that?
    • To what accuracy do we know the distance to the Sun today? How have we measured it?

• Lecture 25 (October 28): Overview of the Solar System.
  • Assigned Reading:
    • Sections 7-1, 7-2, 7-3, 7-4.
  • Summary:
    • The planets in the Solar System are divided into four terrestrial, four Jovian, and Pluto.
    • Terrestrial ones have soid surfaces, are closest to the Sun, made of heavyelements, with small atmospheres of heavy molecules.
    • Jovian planets are very large, with a lot of hydrogen and helium.
    • Pluto is very distant, small, made of ice and rock.
  • Key Questions:
    • How do we measure the mean density of a planet?
    • How could we distinguish a satellite made of ice from one made of rock, if no spacecraft has ever gone there?
    • What will happen to a spacecraft that goes to Saturn and tries to land on it?
    • What are the differences between the atmospheres of the terrestrial planets and those of the Jovian planets?
    • How many objects in the Solar System have atmospheres?

• Lecture 26 (October 29): Our Living Earth.
  • Assigned Reading:
    • Section 9-1, 9-2, 9-3, 9-5.
  • Summary:
    • The Earth is special by the presence of liquid water and life. Water implies oceans, clouds, ice, rain, erosion.
    • The Earth interior is hot from its radioactivity, which causes convection movements in the mantle. These movements make new ocean crust and subduct old one, while continents float and drift on the mantle.
    • The plate motions cause the formation of new mountains.
  • Key Questions:
    • Why is the mean density of the Earth higher than the density of the crust?
    • How do we know the size of the solid, inner core?
    • Why is the Earth's interior so hot?
    • What are the place where we usually have earthquakes and volcanos on Earth?

Week 7 (November 1 - 5) :

The Greenhouse Effect and Global Warming.

• Lecture 27 (November 1): The Earth's Greenhouse Effect.
  • Assigned Reading:
    • Section 9-1, 9-6.
    • Check out the Intergovernmental Panel for Climate Change , the most complete source of information on global warming.
  • Summary:
    • The Earth temperature remains constant if a balance is maintained between incoming solar light and outgoing infrared radiation. When this balance is broken we have a radiative forcing that changes the temperature.
    • The increase in greenhouse gases due to human emissions results in a radiative forcing that today is at 2.4 W/m^2.
  • Key Questions:
    • What is the Earth's albedo?
    • Why does temperature decrease with altitude in the troposphere, and increase with altitude in the stratosphere?
    • What is radiative forcing?
    • If greenhouse gases are increased and the solar flux stays constant, how will the infrared luminosity of the Earth change? How will the Earth surface temperature change?

• Lecture 28 (November 2): The Earth Carbon Cycle and the Ice Ages.
  • Assigned Reading:
    • Section 9.5
  • Optional Reading:
    • Check out the description of the carbon cycle in the Hadley Center for Climate Prediction and Research .
    • Check out the Byrd Polar Research Center , an institution at The Ohio State University dedicated to glaciology research where many studies of present and past climate using glaciers are being done.
  • Summary :
    • The greenhouse effect in the Earth has increased due to anthropogenic emissions of carbon dioxide, methane and other gases.
    • Most carbon dioxide is in the ocean, and its atmospheric concentration was in equilibrium with the ocean until human emissions started. The ocean has absorbed carbon dioxide from the atmosphere since then, but too slowly to prevent it from increasing.
    • The ice ages are thought to be related to variations of the Earth orbit that alter the average solar energy received by Earth, but the temperature variation must be highly magnified by feedback effects (among them, lower greenhouse gases in ice ages) that are poorly understood.
  • Key Questions :
    • How long ago did the last ice age end? How long before that was the last interglacial period?
    • What does the Milankovich theory say?
    • Where is most of the carbon dioxide on Earth?
    • Why was carbon dioxide lower during the ice age than at present?
    • We are now emitting 6 Gigatons of carbon every year. Why is the atmospheric carbon increasing by only 3 Gigatons every year?

• Lecture 29 (November 3): Global Warming and Future Climate Change.
  • Homework 3 handed out.
  • Assigned Reading:
    • Section 9.6
  • Summary:
    • The mean temperature of the Earth has increased by 1 F over the last 100 yars. The increase in temperature is consistent with the modeled response to the radiative forcing of greenhouse gases, plus smaller effects of solar variation, volcanoes, ozone losses, and aerosols.
    • The same climate models predict a much larger temperature increase of 3 to 11 F in the 21st century, which can be partly mitigated if we reduce greenhouse emissions.
  • Key Questions:
    • How much carbon dioxide does each human being release to the atmosphere, on average?
    • Why does sea level rise when temperature increases?
    • Why do aerosols affect global warming?
    • What are the consequences of greenhouse gases that we can be certain of? What consequences are more uncertain?

The Solar System.

• Lecture 30 (November 4): Our Barren Moon.
  • Homework 3 due.
  • Assigned Reading:
    • Sections 10-1, 10-2, 10-3, 10-4, 10-5.
  • Summary:
    • The Moon has no atmosphere because its gravity is too weak to keep gases.
    • The Moon's maria were made of lava flows occurring after large impacts that cracked the crust. The highlands are older, more heavily cratered surfaces.
    • The Moon's interior is more solidified than the Earth's. Moonquakes are weak and caused by the Earth's tides.
    • Crater density denotes the age of a surface. There was an initial epoch of heavy bombardment.
    • The Moon is thought to have formed after the collision of two planets during Earth's formation.
  • Key Questions:
    • Why does it get so much colder at night in the Moon than in the Earth?
    • Why are all the craters round?
    • Why are moonquakes much weaker than Earthquakes?
    • How can the Earth tides produce moonquakes if the Moon is already tidally locked with the Earth?
    • Why does the Moon have less iron than the Earth?

• Lecture 31 (November 5): Cloud-Covered Venus.
  • Homework 4 handed out.
  • Assigned Reading:
    • Sections 12-1, 12-2, 12-3, 12-5.
  • Summary :
    • Venus is permanently covered by clouds of sulfuric acid.
    • The origin of its retrograde rotation] remains a mistery.
    • The greenhouse effect from its thick atmosphere of carbon dioxide causes the temperature to be as high as 460 C.
    • Venus used to have an ocean which evaporated due to runaway freenhouse effect. The carbon dioxide then accumulated in the atmosphere, while hydrogen from water vapor was lost to space.
  • Key Questions :
    • Why is the surface of Venus so hot?
    • Why are there clouds of sulfuric acid in Venus?
    • Why is there so much more carbon dioxide in Venus compared to the Earth?
    • Why is there no water in Venus?
    • Why does the Sun rise on the West in Venus (if you could see it through the clouds)?

Week 8 (November 8-12) :

• Lecture 32 (November 8): Sun-Scorched Mercury.
  • Assigned Reading:
    • Sections 11-1, 11-2, 11-3.
  • Summary:
    • Mercury's surface is heavily cratered and with no atmosphere. Mercury shows also lava plans and scarps. Only Mariner-10 visited Mercury in 1974 so we still do not have a complete map of Mercury.
    • Mercury's rotation period is locked up to 2/3 of its orbital period. This is possible because of the high orbital eccentricity.
    • Mercury has a large iron core. The reason is still unclear, a large collision at the end of Mercury's formation might explain it.
  • Key Questions:
    • Mercury's density is lower than Earth. Why does it then contain a greater proportion of iron than Earth?
    • What is different between the cratered landcapes of Mercury and the Moon?
    • Do you expect taht a future lander on Mercury will find Mercury-quakes?
    • How was Mercury's rotation rate measured?

• Lecture 33 (November 9): Red Planet Mars.
  • Assigned Reading:
    • Sections 13-1 to 13-6.
  • Optional Reading:
    • Construct your own maps of the surface of Mars and other planets from the data that has been sent back by the NASA spacecraft in missions to explore the Solar System, in this website of the U.S. Geological Survey
    • You can access all the images sent to Earth by Mars rovers Spirit and Opportunity in the NASA webpage of the Jet Propulsion Laboratory
  • Summary:
    • Mars' surface is heavily cratered in the South and resurfaced in the North, has large volcanoes, a huge canyon, two polar ice caps of carbon dioxide and water ice that vary seasonally, and a lot of features indicating past water flows.
    • The Martian atmosphere is very thin and made mostly of carbon dioxide. Liquid water probably existed in the past and is in the form of permafrost today. Most of the carbon dioxide was trapped in carbonate rocks by weathering through rain, which was not returned to the atmosphere after volcanic activity ceased. Mars has also lost some atmospheric gases to space.
  • Key Questions:
    • Why did Mars come closer to Earth in the 2003 opposition than at most other times?
    • Why does Mars have volcanoes much higher than any found on Earth?
    • What are clouds in Mars made of?
    • Where is all the water in Mars today?
    • Why is the Martian atmosphere so thin?

• Lecture 34 (November 10): Massive Jupiter.
  • Assigned Reading:
    • Sections 14-1 to 14-6.
  • Summary:
    • Jupiter's atmosphere shows bands and zones resulting from convecitve motions, which generate storms like the Great Red Spot and other ovals. Clouds of ammonia, ammonium hydrosulfide, and water vapor appear at three levels of different temperature.
    • Jupiter emits twice as much radiation as it receives from the Sun, because of its internal heat, which also drives Jupiter's weather.
    • The interior of Jupiter is liquid metallic hydrogen. It probably has a small rocky core in the center.
  • Key Questions:
    • Why is Jupiter a much less spherical planet than Earth?
    • What is the most abundant element in Jupiter? Why?
    • Is the energy of infrared radiation emitted by Jupiter the same as the energy of sunlight that it receives?
    • What do the colors of Jupiter's clouds correspond to? What causes these colors?

• November 11: Veteran's day

• Lecture 35 (November 12): The Galilean Satellites of Jupiter.
  • Assigned Reading:
    • Sections 15-1, 15-2, 15-3, 15-4, 15-6, 15-7.
  • Check the Planetary Society's page to learn more about moons of Jupiter and other cool stuff!
  • Summary:
    • The four Galilean satellites were formed as a miniature Solar System, with rocks close to Jupiter and ice farther away.
    • Their rotations are tidally locked up to Jupiter, and the orbital periods of the first three are trapped in resonances.
    • The slight orbital eccentricities induced by satellite perturbations cause huge tide variations from Jupiter.
    • Io has constant volcanic eruptions and sulfur geysers. Europa has a cracked icy surface and an underlying liquid ocean. Ganymede and Callisto have cratered surfaces, grooved terrain, and more dusty ice.
  • Key Questions:
    • What is peculiar about the orbital periods of the Galilean satellites?
    • Why does Io have so much volcanic activity?
    • What is similar in the way the mean densities of planets in the Solar System and the Galilean satellites vary with the size of their orbits?
    • How can a liquid ocean exist in Europa?

Week 9 (November 15-19) :

• Lecture 36 (November 15): Saturn and its Rings.
  • Assigned Reading:
    • Sections 14-11, 14-12, 14-13, 14-14, 15-8, 15-10.
  • Optional Reading:
    • For the latest news on the Cassini mission and its Huyghens Probe to Titan, check the webpage of the Jet Propulsion Laboratory
  • Summary:
    • Ringed Saturn is the least dense and the most oblate planet.
    • The rings are made of ice particles orbiting in hundreds of ringlets, shaped by gravitational perturbations of Saturn's satellites.
    • The atmosphere and interior of Saturn are similar to Jupiter, but Saturn has a larger rocky core.
    • Titan is the only satellite with an atmosphere, made of nitrogen. Its surface is likely covered with hydrocarbon lakes. In about a year we may find out more about this world with the Huyghens probe.
  • Key Questions:
    • Why could Saturn's rings not be made of a solid piece of matter?
    • Why is the albedo of the rings so high?
    • Why is Saturn's density lower than Jupiter's?
    • Why does Titan have a nitrogen atmosphere but the Moon doesn't?

• Lecture 37 (November 16): Uranus and Neptune.
  • Homework 4 due.
  • Assigned Reading:
    • Sections 16-2, 16-3, 16-4, 16-6,, 16-7, 16-8.
  • Summary:
    • Uranus's equator is inclined close to 90 degrees relative to the plane of its orbit.
    • Neptune has more clouds than Uranus owing to convection, due to its internal heat. The clouds are made of methane droplets.
    • Uranus and Neptune have small, dark rings made of ice particles with a coating of dark carbon.
    • Uranus and Neptune have a larger proportion of their mass as a rocky core than Jupiter and Saturn, and contain also more methane, ammonia and water.
    • Triton is a large satellite of Neptune in retrograde orbit, probably a captured asteroid that has suffered large tides and internal heating.
  • Key Questions:
    • If you lived in Uranus at a latitute of 40 degrees, how long would the night be in Winter? How long would it be in Summer?
    • Why are Uranus and Neptune blue?
    • What is different in the composition of Uranus and Neptune compared to Jupiter and Saturn?
    • How were rings around Uranus and Neptune detected?
    • Why are the moons and rings of Uranus so dark?

• Lecture 38 (November 17): Pluto and the Kuiper Belt.
  • Homework 5 handed out.
  • Assigned Reading:
    • Sections 16-9.
  • Summary:
    • Pluto was discovered in 1930 by Tombaugh. It is the smallest planet with a diameter of 2300 km, and a highly inclined and eccentric orbit. The only details from its surface are very blurry, from Hubble Space Telescope images.
    • Pluto has the moon Charon, very large in relation to its planet (1200 km diameter), and is tidally locked up to Pluto.
    • Pluto and Charon form part of the Kuiper Belt, a large number of icy, small objects orbiting beyond Neptune.
  • Key Questions:
    • Are there craters in Pluto?
    • How has Pluto been affected by Neptune?
    • What does the average density of Pluto of 2 grams per cubic centimetre suggest?
    • What class of objects does Pluto belong to?

• Lecture 39 (November 18): Asteroids, Meteorites, and Meteors.
  • Homework 5 due.
  • Assigned Reading:
    • Sections 17-1 to 17-6.
    • Check out the Near-Shoemaker website, on the spaceship that orbited asteroid EROS and landed on it in 2001.
  • Summary:
    • Asteroids were discovered starting in 1801, today there are more than 10000 known, most of them orbit between Mars and Jupiter.
    • Jupiter's gravitational tugs cause gaps in the distribution of asteriod periods, called Kirkwood gaps.
    • Several spacecraft have taken images of asteroids. They are irregularly shaped, some of them are made of various pieces and may have moons.
    • Asteroid sometimes collide with Earth, one collision 65 million years ago caused a major extinction and left a layer of iridium all over the planet. Asteroids are also the origin of meteorites.
  • Key Questions:
    • How were asteroids discovered?
    • What is different in the composition of asteroids and Kuiper Belt objects?
    • What is special about Trojan asteroids?
    • How are meteorites and asteroids related?
    • Why are many asteroids not spherical?

• Lecture 40 (November 19): Comets.
  • PAPER DUE.
  • Assigned Reading:
    • Sections 17-7, 17-8, 17-9.
  • Summary:
    • Comets are small objects made of ice and dirt. They are in very eccentric orbits. When they reach perihelion and are close to the Sun, the ices sublimate and generate bright and extended tails.
    • Comets come from the outskirts of the Solar System, in the Oort cloud or the Kuiper Belt. They have spent billions of years in that region, and they become visible when some gravitational perturbation reduces their perihelion, making them pass close to the Sun. As their ices evaporate, they generally do not last for many orbital periods before they break into pieces.
  • Key Questions:
    • What is a comet nucleus made of?
    • Why is a comet nucleus so dark?
    • How are comets and meteor showers related?
    • In which direction does the ion tail of a comet point?
    • Why are comet orbits very highly eccentric?

Week 10 (November 22-24) :

• November 22: Review day

• November 23: MIDTERM II EXAM , Lectures 23 to 41.

• November 24: Free Topic Lecture Day.

• November 25, 26: Happy Thanksgiving.

• Lecture 41 (November 29): The Formation of the Solar System.
  • Assigned Reading:
    • Sections 8-1, 8-2, 8-3, 8-4, 8-5; Section 9-5.
  • Summary:
    • The primordial solar nebula collapsed gravitationally from intestellar space, and had the abundance of elements determined by the synthesis of nuclei in stellar interiors.
    • As it collapsed, it formed a disk of gas and dust around the main lump of mass in the center that was to become the Sun.
    • Dust grains aggregated into planetessimals, which came together and grew to become the planets.
  • Key Questions:
    • If you take an oxygen atom today, where was its nucleus first made?
    • If that oxygen atom was in the atmosphere in the primitive Earth, what molecule would it most likely be part of? If at present it is part of an oxygen molecule, how was that molecule likely made?
    • Why is there so little water in the terrestrial planets and so much in the satellites of the giant planets?

• Lecture 42 (November 30): Exoplanets I.
  • Assigned Reading:
    • Section 8-6.
    • Check out this webpage on Exoplanets , plus the Extrasolar Planets Encyclopaedia , and the NASA webpage on current plans for a Terrestrial Planet Finder .
  • Summary:
    • 127 exoplanets have been discovered. For most of them, we have only measured the velocity of their parent star through the Doppler effect, and the way the velocity changes owing to the gravitational tug of the planet moving around it. For a few cases, we have observed a slight dimming of the star caused by the transit of the planet over the star. Some of these are in systems of two or three planets.
    • Most of the detected planets are very massive (similar to Jupiter), because our measurements are not accurate enough to detect less massive planets. As technology for very precise Doppler measurements of velocity has progressed, we have recently been able to find planets of the mass of Neptune, but only when they are very close to their star.
    • Most planetary systems seem very different from the Solar System: some giant planets are very close to their star, most others are in highly eccentric orbits. But a few are in orbits similar to Jupiter in the Solar System.
    • In the future, we expect to find Earth-like planets using more sensitive methods. How many there will be, and how many will have orbits adequate to sustain life, is a big unknown.
  • Key Questions:
    • How many planets outside the Solar System have been discovered so far?
    • What methods have been used to discover these planets?
    • How are these planets different from the ones in the Solar System?
    • Why are all known exoplanets about as massive as Jupiter, and none are like the Earth?

• Lecture 43 (December 1): Exoplanets II.
  • Make-up Homework handed out.
  • Assigned Reading: same as previous lecture.

• December 2: Student Presentations.
  • Make-up Homework due.

• December 3: Review