Sunday last day for blog posts

Jackie here. I don't want there to be pressure on you to write blog posts during exam week, and I need to eventually win the race to grade blog entries faster than you all post them, so I'm not going to grade any blog posts that are posted after Sunday evening 12/4 (ie if they say Monday 12/5, they're still awesome but they're not for points). If you think you really really need to post more blogs next week in order to get the grade you want to get, let me know. But currently you are all pretty much doing fantastic, so don't stress about it too much.

Prof. Johnson on TV

Tomorrow at 6pm and 9pm on the National Geographic Channel. Yes, this will be on the final (just kidding).

Finding the Next Earth

Join astronomers as they enter the final lap in a race to find a planet capable of sustaining life, a world like ours, the next Earth. See the launch of Frances CoRot and Americas Kepler missions, and the smoking hot worlds they discover. See a controversial and tantalizing discovery of a planet where life could exist in a strange twilight zone, that is, if the planet really exists. Astronomers are working to determine what conditions are necessary for life to exist, and they are building the radical James Webb Space Telescope, a spacecraft that can look at the atmosphere around a planet and reveal whether or not life as we know it actually exists. It could be the greatest discovery in human history and it could change how we see ourselves.

TQFR

Please be sure to fill out your TQFR (Teaching Quality something something) surveys at the end of the term. We will listen closely to your feedback, which we'll incorporate into adjustments to the Ay20 course in future terms. Thanks!

Essential Topics

Essential topics from the class to study for your exam:

• What is the relationship between telescope diameter and resolution?
• Celestial sphere: when will a star at a given RA and dec be visible in the sky?
• What are the equations of stellar structure, and the story of each one?
• Scaling relations (what they are and how to derive them): M-R, M-L, M-Teff
• Use scaling relations to derive the slope of the main sequence in the H-R diagram (log L vs -log Teff)
• Derive the slope of the white dwarf main sequence
• Equilibrium temperature of a planet as a function of semimajor axis and stellar properties
• Blackbodies! Flux, luminosity, Rayleigh-Jeans Law (kT >> h*nu), Wien's Law (kT << h*nu), peak wavelength (relationship between photon energy and temperature)
• Color and brightness of a star
• Virial theorem - what does it mean? apply it to:
• white dwarf (mass-radius)
• typical temperature in the Sun
• derivation of Kepler's 3rd law
• How do we find planets?
• Relationship between velocity amplitude of a Doppler signal and mass of planet, period of planet, mass of star

Optional Lab: Exoplanet Transit

The Las Cumbres Observatory Global Telescope Network has a program called Agent Exoplanet where you go through real astronomical images from their telescopes, measure the flux from stars, and then identify stars with transiting planets based on a dip in flux. If you would like to earn extra points, or if you're just curious, please go play with their tools and then blog it up!

Transit Probability

Many of you had some trouble with the worksheet problem about the transit probability of a planet. Consider the sketch below:

The star is the big orange circle in the middle, and the filled blue circles show two extreme planet-orbit inclinations, above and below which the planet does not transit. Note that the orbit planes for the two configurations are parallel to the blue solid lines, not the black lines. The two orbit configurations are separated by and angle of approximately 2 Rstar/a (purple trace), obtained using the "skinny angle" property that the sine of a small angle is the small side over the long side.

With those definitions in mind, the transit probability is related to the solid angle traced out by the two extreme transit configurations, which is

as well as the total solid angle at a semimajor axis a, or:

The probability is the ratio of these two solid angles:

For more on all things transit, including eccentric orbits and other properties of the transit geometry, see Prof. Josh Winn's (MIT) excellent book chapter here:

http://arxiv.org/pdf/1001.2010v4

RV Plots for Thursday's Worksheet

Here are the radial velocity time series for two exoplanets. The mass of the star is listed under each plot. Problem 1 on the worksheet asks you to measure the masses of the planets in each system (assume e = 0, and i = 90 degrees).

 Mstar = 1.8 Msun

 Mstar = 1.7 Msun