Some Philosophy

As with exam 1, use the lecture notes and the problem sets as the primary guideline for preparation for the test. I will not be pulling specific topics out of the book but rather emphasizing general principles as highlighted in the notes. The test will consist of 2 or 3 problem-set-like questions and a dozen or so more qualitative or quantitatively-simple questions that have been selected so that they are doable overall in the 50 minutes. That is, the same format as Exam 1.

The links on the notes page under each lecture are for your interest. I'm not expecting you to study those external sources for the test (unless I comment explicitly below).


Spectral lines - Know the basic of where the Rydberg equation comes from and the equaton itself. Make sure you know the Rydberg constant (in nanometers is fine). Understand the equation of electrostatic attraction and centripetal acceleration under the constraint that angular momentum be quantized in units of h/2pi. Know what an electron volt is in units of Joules. Be able to convert a wavelength to a photon energy in electron volts or Joules. Understand the circumstances under which you see emission lines vs. absorption lines in the spectrum of an object or a gas cloud. Be able to do a simple calculation using the Doppler equation. Know how broad a spectral line should be given the temperature of the gas (kT --> typical velocities --> Doppler equation).

Understand the two basic telescope types and why the largest telescopes in the world are of the reflecting variety. Understand the definition of the focal length of a telescope objective and how it relates to magnification when you know the focal length of the eyepiece. How do you calculate the platescale (arcsec/mm) at the focal plane of a telescope if you know the focal length? Qualitatively describe spherical aberration and chromatic aberration. Know what an Airy pattern is and how to calculate its blurring effects knowing the wavelength of observation and the size of the aperture. What kind of spatial resolution (that is angular resolution) will you get out of an interferometer with a spacing of 50 kilometers between antennae working at a wavelength of one centimeter? Understand how Poisson statistics (i.e. a counting experiment) limit the signal-to-noise ratio when you are counting a finite number of photons. How many photons do you need to count to obtain 2% precision (SNR=50).

Understand the basic distribution of mass in the solar system and difference in composition vs. distance from the Sun (Jovian vs. Terrestrial worlds). Know the common characteristics in the solar system that point to origin in a thin flat disk. Explain why hydrogen and helium gas had little part in the process of planetary growth through accretion. Describe the basic characteristics of Molecular clouds. What does sound speed in the cloud have to do with the size scale over which the cloud is unstable to gravitation collapse. Can you describe qualitatively why there should be a minimum size/mass for collapse using "sound speed" and "freefall time"? What molecule is best used for mapping molecular clouds? Why is this rare molecule preferred rather than the more common molecular hydrogen? What is the relative abundance of the most common atoms - Hydrogen, Helium, Carbon/Nitrogen/Oxygen/Silicon (not precisely but rough order of magnitude).

What's the typical random velocity of gas in a molecular cloud (which comes into play in a significant way in describing how a cloud collapses and forms a disk). How far away are the nearest star forming regions? How large a spatial scale does an arcsecond subtend at this distance? How does this scale compare to the size of the Solar System? How does conservation of angular momentum limit the degree to which a rotating molecular cloud can collapse leading to the formation of a disk. Given the size scales show that this radius is comparable to the size of the solar system. What evidence is there that these disks really exist in nature? How can blackbody radiation, Wein's law, and the distribution of infrared light as a function of wavelength reveal the presence of and structure of such disks. What is a Debris Disk and how does it relate the the process of solar system formation and the evolution of circumstellar disks. How much mass should one expect to find in one of these circumstellar disks.

How does local temperature dictate what composition of particles participate in the accretion process? What does this have to do with the formation of Jovian planets (and the composition of their moons) and where we expect to find those planets in a forming solar system?

Know how, in a simplistic way, half-life can provide a guide to the radiometric age of a sample that once was originally 100% composed of a radioactive isotope. Understand the complication of initial contamination by the atoms masquerading as the decay product (that is, contamination by those atoms at the time of formation of the rock), and how uninvolved isotopes of that decay product can provide the missing information via isochron plots. What do meteorites have to say about the timing of the formation of the solar system. How are calcium-aluminum inclusions related? Can you, even broadly, explain how hafnium-tungsten abundances are related to understanding the timing of the formation of the Earth's core?

Understand why direct detection of extrasolar planets is difficult and why prospects for direct detection improve at infrared wavelengths. Be able to describe and apply the two methods for indirect detection of extrasolar planets. What aspects of currently discovered extrasolar planetary systems don't match up to our expectations for the architecture of planetary systems based on accretion theory. How do we theorize ourselves out of the dilemma? Understand the differece between cold start (accretion) origins for giant planets and hot start (gravitational instability) and what observational diagnostics might distinguish between them.

Note that all discussion of cratering and crater counting will be saved for the final exam.




Physical Constants you need to know

Speed of light - c
Planck's constant - h
Boltzmann's constant - k
Stefan-Boltzmann constant - sigma
Gravitational constant - G
Mass of the Sun
Mass of the Earth
Radius of the Earth
Earth-Sun separation in AU and in meters