ASTR110G 

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Learning Objectives for Lectures

  1. The Contents of the Universe
    1. Review and absorb the course requirements and syllabus.
    2. Become comfortable estimating the sizes of astronomically relevant objects across a large range of sizes, from the very small (sub-atomic particles) to the very large (super-clusters of galaxies like the Milky Way).
    3. Realize that on every size scale, the Universe is primarily empty space.
    4. Understand that on every size scale, the Universe contains a large number of objects with similar properties.
    5. Become familiar with the appearance of a range of common astronomical objects, such as asteroids, comets, satellites, planets, stars, and galaxies.

  2. Scientific Notation
    1. Review the mathematics necessary for successful completion of this course.
    2. Become comfortable with multiplying and dividing numbers expressed in scientific notation.
    3. Understand square roots, cubic roots, fourth roots, and powers of ten.
    4. Master unit conversions, such as changing a speed in units of miles per hour to units of feet per second.

  3. Timescales in the Universe
    1. Visualize the position of solar system and galactic objects in scale models of the Milky Way galaxy.
    2. Become comfortable estimating the lengths of astronomically relevant events over a large range of times, from the very short (atomic transitions, passage of light from the Moon to Earth) to the very long (time for light from distant quasars to reach Earth).
    3. Realize that astronomical events can take place on timescales far longer than a human lifetime, and thus typically we cannot track the evolution of individual objects.
    4. Understand that due to the finite speed of light, a telescope functions in essence like a time machine when viewing distant objects, seeing them not as they are today but as they were billions of years ago.

  4. The Phases of the Moon
    1. Understand how the phase of the Moon is controlled by the relative positions of the Sun and Moon in the sky.
    2. Comprehend that the Sun always illuminates a full half of the Moon, but that we can see a fraction (something between all and none) of the illuminated portion from Earth at any given time.
    3. Realize that at any time the Moon can be seen from only half of the Earth's surface.
    4. Diagram how the Moon's monthly cycle of movement around the Earth causes it to pass through its eight apparent phases from Earth.
    5. Visualize the phase of the Moon for each position around the Earth, relative to the Sun.
    6. Predict when the Moon will rise, lie almost overhead, and set, during each lunar phase.
    7. Visualize the east-west positions around the Earth as forming a 24 hour solar clock.

  5. The Seasons on Earth
    1. Understand how the seasons vary over the surface of the Earth
    2. Comprehend the role that the tilt of the Earth and the distance between the Earth and the Sun play in driving the seasons.
    3. Predict how the seasons would vary for a planet, based on its orbital eccentricity (deviance from a perfect circle) and its axial tilt.
    4. Utilize the scientific method to explore and to solve problems.

  6. The Origin of the Moon
    1. Visualize the formation of the solar system.
    2. Understand the four hypotheses which attempt to explain the origin of the Moon.
      1. A sister planet to Earth
      2. A captured asteroid
      3. A spun-of fragment of the Earth
      4. A relic of a proto-planetary collision
    3. Evaluate the evidence in support of and against each hypothesis.
      1. How does the distribution of different isotopes of oxygen compare on the Earth and the Moon?
      2. Does the Moon have a large iron core?
      3. Was the Moon composed of heated, melted materials?
    4. Argue convincingly that the Moon was most probably created in a near-catastrophic collision.
    5. Understand how gravitational attraction scales with mass and distance.
    6. Differentiate between force and acceleration (weight and surface gravity).

  7. The Celestial Sphere
    1. Visualize the effect that the following factors have on the stars as observed from Earth
      1. The 24-hour rotational cycle of the Earth on its own axis
      2. The 23 degree tilt of the Earth's rotational axis toward, and away from, the Sun
      3. The yearly rotation of the Earth around the Sun
    2. Predict the appearance of the sky as viewed from the poles, the equator, or an intermediate position on Earth, over a night, a month, or a year.
    3. Understand why the Sun seems to change color between sunrise, noon, and sunset.

  8. Planetary Orbits
    1. Understand Kepler's Three Laws of Planetary Motion.
      1. Relate the three laws to the underlying force of gravity.
      2. Visualize the effect of the three laws on the orbits of planets, asteroids, and comets.
      3. Calculate an orbital radius from an orbital period, or an orbital period from an orbital radius.
    2. Understand how the shadows cast by the Earth and Moon on each other produce lunar and solar eclipses.
    3. Become comfortable with such terms as opposition and conjunction when describing the locations of the planets in the sky.

  9. The Scientific Method
    1. Visualize the way in which the Earth's motion around the Sun produces retrograde motion in other planets.
    2. Predict the phases of neighboring planets based on their relative positions and the location of the Sun.
    3. Understand the role that key individuals play in advancing scientific knowledge.
    4. Comprehend the point of the scientific method in testing and refining hypotheses to explain the world around us.
    5. Review statistics and plotting techniques for laboratory exercises.

  10. Geocentric and Heliocentric Models
    1. Understand the geocentric (Earth-centered) and the heliocentric (Sun-centered) models of the solar system.
      1. Define the key difference between the two models.
      2. Visualize how the deferents and epicycles of the geocentric model could vary the observed size and brightness of a planet over time.
      3. Critique Aristotle's arguments against the heliocentric system.
      4. Visualize how retrograde motion could be achieved within each model.
      5. Comprehend whether or not parallax would occur under each model.
      6. Sketch the observed phases of Venus within each model.
    2. Comprehend the parallax effect, and its scaling with orbital radius and with the distance to a nearby star.
    3. Grasp how key observations made by Galileo with the newly invented telescope contradicted the geocentric cosmological model of his day.

  11. The Formation of the Planets
    1. Visualize how gravity condenses a cooling solar nebula of gas and dust into a dense star, surrounded by a rotating disk of proto-planetary material.
    2. Connect the uniformity of the planets' orbits and axial tilts to a common origin.
    3. Motivate the rocky composition of the Terrestrial planets with their central positions, near to the hot Sun.
    4. Explain the large gas components of the Jovian planets as a function of their cooler environment and larger sweeping radii.
    5. Understand the role that radioactive dating plays in determining the ages of various bodies in the solar system.

  12. The Terrestrial Planets
    1. Understand the form and the significance of the four critical phases of evolution for Terrestrial planets.
    2. Comprehend what controls the severity of differentiation, cratering, flooding, and surface evolution on each planet.
    3. Compare and contrast the surface and atmospheric evolution of Earth, Mercury, Venus, Mars, and the Moon.
    4. Consider the five suggested definitions for a planet, and discriminate between them.

  13. The Jovian Planets
    1. Understand how the outer planets differ in size, mass, density, and composition from the inner planets (rocks versus soap bubbles).
      1. Visualize how the solar system formation process forced the volatile hydrogen and helium gases out to large radii from the Sun before they condensed.
      2. Imagine a gas giant as being primarily layers and layers of atmosphere, with very little solid surface below.
      3. Appreciate the beauty of the many rings and satellites surrounding the Jovian planets.
    2. Understand how the planetary mass and the distance from the Sun produce a range of Jovian planets, from massive, nearby Jupiter to remote, icy Neptune.
    3. Understand the wide range of formation scenarios for the Jovian satellites (asteroids or comets that passed too close, co-forming objects, accreted planetoids).
    4. Comprehend the role of tidal forces in transferring heat to the satellites of the Jovian planets, making them more likely environments to support life.
    5. Visualize the pattern of nights and days on Earth if Jupiter were to shine almost as brightly as the Sun (or within a binary solar system, with two stars).
    6. Empathize with (dwarf) planet Pluto, a historical planet whose very nature is under review.

  14. Waves and Light
    1. Understand the concept of a wave, and describe common examples of wavelike behavior found in nature:
      1. The wave pattern caused by fans raising and lowering their arms in concert in a soccer stadium
      2. Sound waves moving through the air, or earthquake waves moving through the ground
      3. Music, where varying the length of a string or the length of a pipe produces a change in pitch
      4. Ocean waves, crashing up on the shore with a certain rhythm
      5. The wavelike pattern of a child's swing, moving forward and backward
    2. Visualize the major regimes along the electromagnetic spectrum, and connect them to our daily lives.
      1. Gamma-rays (high energy, emitted by unusual distant objects called gamma-ray bursters)
      2. X-rays (ideal for photographing bones underneath muscle)
      3. Ultraviolet radiation (emitted by the Sun, harmful to humans)
      4. Optical light (transmitted by our atmosphere, ideal for our eyes)
      5. Infrared heat (not visible, perceived as heat)
      6. Radio waves (low energy, where human technology pollutes the extragalactic sky)
    3. Comprehend how to characterize a wave by its energy, its frequency, its wavelength, or its color.
      1. Relate energy to frequency, frequency to wavelength, wavelength to color, and suchlike.
      2. Understand the effect of increasing the amount of energy per photon in a beam of light.
      3. Contrast with the effect of increasing the number of photons in a beam of light.
      4. Realize that though light can have different frequencies, it always travels at the same speed.
    4. Visualize the effects of driving a system (a bridge, or a child's swing) at its resonant frequency.

  15. Atomic Structure
    1. Understand the internal structure of the atom.
      1. Place heavy protons and neutrons in the nucleus, light electrons in a cloud surrounding it.
      2. Connect atomic number (number of protons) to element (hydrogen, helium, lithium, etc.).
      3. See how experimentation improved our visualization of the atom.
      4. Become comfortable with the notation used to describe atomic species (such as 12C6 for carbon).
    2. Comprehend the key features of the Bohr model.
      1. Electrons can exist only at set, spaced orbitals (energy levels) within an atom.
      2. An atom must absorb energy to shift an electron to a higher energy level.
      3. An atom must emit energy to shift an electron to a lower level.
      4. The pattern of absorption and emission from an atom is like a fingerprint, and reveals which element it is.
    3. Relate the energy levels within an atom, and their population with electrons, to the pattern of emission and absorption seen in spectra when observing an element in space.
    4. Embrace the key findings of quantum mechanics.
      1. Energy is quantized into packets, and cannot be divided into arbitrarily small amounts.
      2. The act of observing alters the reality under observation, at the sub-atomic level.

  16. Absorption and Emission
    1. Relate the color of an object to the energy that it is emitting or reflecting.
    2. Describe the source and appearance of three types of spectra.
      1. Continuum spectra, where a continuous distribution of light is emitted by the cores of stars
      2. Absorption spectra, where key wavelengths of light are removed from core continuum spectra by the atmospheres of stars or by cool clouds of gas
      3. Emission spectra, where light absorbed at key wavelengths from continuum spectra are reflected in a random direction from a cool cloud of gas
    3. Connect one- or two-dimensional images of spectra to the emission or absorption of light within atoms in an object (such as a star).
    4. Separate the intrinsic properties (luminosity, temperature, radius, chemical composition) of stars from the apparent property (observed brightness), which varies with distance.
    5. Use the magnitude system to compare stars of varying brightness and colors.

  17. Stellar Temperatures
    1. Connect the temperature of a stellar core to the strength of its hydrogen absorption features.
    2. Relate the chemical composition of a star to changes in features in its spectrum.
    3. Know the pattern of stellar types and temperatures (O - B - A - F - G - K - M - L - T).
    4. Relate the temperature of a stellar core to the likelihood of molecules surviving in its atmosphere.
    5. Visualize the colors shown in Hubble Space Telescope images of star and planetary nebula as indicating the presence of key elements.

  18. Nuclear Reactions
    1. Understand the fundamental forces of gravity, electromagnetism, and the nuclear force, and their interplay on large and small size scales.
    2. Visualize the fission process.
      1. Comprehend how the fusion process acts to divide unstable (radioactive) nuclei.
      2. Connect the difference in mass between the initial reactants and the final products to the energy emitted.
      3. Evaluate the importance of fusion within the Sun by considering the amount of available radioactive materials in the core.
    3. Visualize the fusion process.
      1. Relate the temperature and pressure within the solar core to the probability that two protons can join (fuse).
      2. Connect the mass lost in the fusion process to the emission of energetic gamma rays.
      3. Quantify the amount of hydrogen which must undergo fusion every second in order to power the luminosity of the Sun.

  19. Binary Stars
    1. Understand how a moving source can produce Doppler shifts (blue and red).
    2. Visualize the effect of blueshift and redshift on key features in star and galaxy spectra.
    3. Connect the relative masses of stars to their center of mass.
    4. Define various types of stellar combinations: optical and visual doubles, and single- and double-lined spectroscopic binaries.

  20. The Hertzsprung-Russell Diagram
    1. Understand the difference between apparent properties, which vary with distance, and intrinsic properties.
    2. Become comfortable reading and plotting the H-R Diagram.
      1. Connect the x-axis to temperature, to color, and to stellar type.
      2. Connect the y-axis to luminosity and to mass.
      3. Visualize lines of constant radius, stretching from the upper left to the lower right.
      4. Chart the range of the Main Sequence, where stars shine for most of their lives.
      5. See why the giant phase stretches up and to the right, to higher luminosities and lower temperatures.
      6. See why the white dwarfs are located in the lower left corner, indicating fairly high temperatures and fairly low luminosities.
    3. Connect the radial velocity (Doppler shift) of a star in orbit around a companion to the companion's mass.
    4. Visualize how white dwarfs cool, and so shift to lower temperatures and lower luminosities over time.
    5. Understand how telescope sensitivity means that we can detect the faintest stars only near to our solar system, while bright stars can be found out to far larger distances.
    6. Connect the fundamental properties of luminosity, temperature, and radius for stars. Become comfortable manipulating them algebraically.

  21. White Dwarfs
    1. Trace the passage of higher and lower mass stars through the H-R Diagram.
      1. Relate the lifetime of a star on the Main Sequence inversely to its mass.
      2. For high mass stars, a brief stint (millions of years) on the high end of the Main Sequence, then off to the Supergiant space, ending as neutron stars or black holes.
      3. For intermediate and low mas stars, billions of years on the Main Sequence, then ascension to the Giant branch, and then a drop down to the region where white dwarfs are found.
      4. Understand how Giant stars can increase in luminosity and yet decrease in temperature.
    2. Determine the end-state of a stellar core from its initial mass.
      1. Low mass stars (1 - 10 solar masses) become white dwarfs.
      2. Intermediate mass stars (10 - 30 solar masses) become neutron stars.
      3. High mass stars (more than 30 solar masses) become black holes.
    3. Understand how the accretion of hydrogen from a companion object onto a white dwarf can produce a bright supernova.
    4. Visualize how the strong pressure of self-gravity on an object the mass of the Sun but the size of the Earth will act to ionize the carbon and iron atoms, producing a lattice of carbon (diamonds!) and a sea of disassociated electrons.
    5. Appreciate the physical beauty of white dwarfs and their surrounding gas shells.

  22. Neutron Stars
    1. Understand the life-cycle of intermediate mass stars.
      1. An initial solar nebula collapse results in an intermediate-mass star, which burns hydrogen on the Main Sequence for billions of years.
      2. Once hydrogen and helium resources have been consumed, the star enters the red supergiant phase, expanding in size and luminosity but decreasing in temperature.
      3. In the supernova phase, the star expels metals (carbon, oxygen, ...) into the surrounding interstellar medium, seeding future solar systems.
      4. The remaining carbon, oxygen, calcium, and silicon in the core are fused together, forming a dense iron core roughly the size of the Earth.
      5. The self-gravitational force is so strong that the iron atoms melt into hydrogen, and the constituent protons and electrons are forced together, forming a sea of pure neutrons and producing a core collapse supernova in which this single star briefly outshines an entire galaxy.
    2. Visualize a neutron star as a star-mass object compressed into a volume the size of Las Cruces (a tablespoon of neutron star material weighs as much as a mountain).
    3. Comprehend how the rotation of the neutron star will be magnified by the collapse process, just as ice skaters speed up by pulling their arms and legs inwards, producing pulsars which rotate 1,000 per second.

  23. Black Holes
    1. Relate the concept of escape velocity to a black hole (an object whose escape velocity is greater than the speed of light within the event horizon).
    2. Visualize a black hole as an object with finite mass, infinite density, and zero size.
    3. Understand how the strong increasing gravitational force of a black hole will separate your toes from your nose (due to the differential tidal force).
    4. Visualize the consequences of gravitational fields affecting the passage of time.
      1. Time passes slower in the presence of a stronger gravitational field.
      2. Time is thus a relative quantity - there is no absolute clock keeping correct time.
      3. The difference in clock speeds can actually be measured by placing clocks closer to or further from the Earth's surface.
      4. A spacecraft approaching the event horizon of a black hole will thus appear to travel slower and slower, from the point of view of a distant observer.
      5. A spacecraft approaching the event horizon of a black hole will thus observe the rest of the universe fast-forwarding through the rest of its lifetime, from the point of view of the pilot.
    5. Visualize the effect of gravitational lensing on a star field (strong gravity can bend light rays).
    6. Understand how a black hole in a binary star system can gain fuel from its companion, creating an accretion disk.
    7. Comprehend the consequences of replacing the Sun with a black hole.

  24. The Milky Way
    1. Consider the key points made in the Shapley-Curtis debate about the nature of spiral nebulae, and evaluate the observational evidence.
      1. Shapley thought the Milky Way was 300,000 light-years in diameter, and not centered around the Sun. He concluded that spiral nebulae were local clouds of gas.
      2. Curtis argued that the Milky Way was only 30,000 light years in diameter, was centered around the Sun, and that spiral nebulae were island universes located beyond the Milky Way.
      3. Shapley's estimate of the size of the galaxy was fairly good, and he was absolutely correct that it is not heliocentric. However, he did not realize that the spiral nebulae were external galaxies, similar in nature to the Milky Way itself.
      4. Shapley assumed that all globular clusters were similar in size, mapped their distribution, and used parallax measurements of the distance to one globular cluster to determine the size and extent of the Milky Way. [good data, reasonable analysis, good conclusions]
      5. Curtis' analysis of the globular cluster data produced a significantly smaller size estimate for the Milky Way.
        [good data, difficult analysis, flawed conclusions]
      6. Leavitt's observations and analysis of variable stars in the nearby Magellanic Cloud galaxies showed that stellar period correlated with the intrinsic luminosity for these objects. Shapley deduced a distance to the Magellanic Cloud's which lay within the Milky Way, and concluded that spiral nebulae lay within it, perhaps being late-forming solar systems.
        [good data, risky analysis, biased sample, flawed conclusions]
      7. van Maanen measured a rotational speed for M101 of 0.02 arc-seconds per year, forcing it to either lie within the Milky Way or to rotate faster than the speed of light.
        [inaccurate data, reasonable analysis, flawed conclusions]
      8. Recessional velocities for spiral nebulae implied that they were close to the Milky Way, near enough to be profoundly influenced by it.
        [good data, incomplete analysis, flawed conclusions]
      9. Curtis' study of spiral nebulae spectra showed them to be indistinguishable from the Galactic spectrum, suggesting a common form.
        [good data, good analysis, good conclusions]
    2. Connect emission peaks and absorptions troughs in galaxy spectra to atomic transitions within atoms, and to chemical composition.
    3. Calculate redshifts and blueshifts for galaxies, based on wavelength offsets in position of features based on rest-wavelengths.
    4. Connect the recessional velocities of galaxies with their distance from the Milky Way.
    5. Calculate distances to galaxies based upon their redshifts and blueshifts.
    6. Visualize how an expanding Universe causes galaxies to appear to be receding, when viewed from the Milky Way or from any other galaxy.

  25. The Expansion of the Universe
    1. Visualize one-, two-, three-, and four-dimensional Universes, by analogy to lines (strings), planes (pieces of paper), and so on.
    2. Imagine how physical space could have no end, by bending a line into a circle, a plane into a sphere (the surface of a balloon), and so on.
    3. Consider how a Universe could expand into a higher dimension. A one-dimensional Universe appears as a straight line from within, but could be a curved space (a circle), expanding into a second dimension. A two-dimensional Universe appears as a flat plane from within, but could be a curved space (the surface of a sphere), expanding into a third dimension. A three-dimensional Universe appears as does our own world, but could be a curved space, expanding into a fourth dimension ...
    4. Contrast the Steady State and the Big Band models of the Universe.
    5. Connect mean density and gravity to the idea that the Universe is either open, expanding outwards in size forever, or closed, doomed to collapse inward in the end.

  26. A Universe of Galaxies
    1. Understand the distribution of galaxy properties along the Hubble Tuning Fork.
      1. For ellipticals: a smooth structure, no disk, axial ratio determines sub-classification.
      2. For spirals: importance of bulge, strength and tightness of spiral arms within disk all determine sub-classification.
      3. For barred spirals: spiral properties, plus a central bar.
      4. For lenticulars: large bulge, a disk-like structure without spiral arms, for an intermediate classification between elliptical and spiral.
      5. For irregular and peculiar galaxies: non-symmetric distributions of light (train-wreck), possibly caused by interaction with another galaxy.
    2. Visualize the basic form of our Milky Way galaxy, and of all spiral galaxies.
      1. A central bulge, made up of old, red stars.
      2. A disk-like structure full of young, blue stars, gas, and dust, characterized by spiral arms.
      3. A diffuse halo of old, red stars, dense globular clusters, and mysterious dark (non-luminous) matter.
    3. Visualize the basic form of elliptical galaxies.
      1. A large smooth structure, similar to the central bulge of a spiral galaxy.
      2. The absence of significant gas reservoirs, implying an old population of stars and little potential for future star formation.
      3. High mass, red colours, often found within large clusters of galaxies.
      4. Might form from the merging of two spiral galaxies.