1. Review for Test #2 October 12 Topics: Radiation and the Electromagnetic Spectrum - Black bodies Atoms and Spectroscopy - Doppler Effect, Bohr model The Solar System and its Formation Methods Conceptual Review and Practice Problems Review lectures (on-line) and know answers to clicker & HW questions Try practice quizzes on-line (in MA) Bring: Two Number 2 pencils Simple calculator (no electronic notes) Reminder: There are NO make-up tests for this class

2. Test #2 Review How to take a multiple choice test 1) Before the Test: Study hard Get plenty of rest the night before 2) During the Test: Draw simple sketches to help visualize problems Solve numerical problems in the margin Come up with your answer first, then look for it in the choices If you can’t find the answer, try process of elimination If you don’t know the answer, Go on to the next problem and come back to this one later TAKE YOUR TIME, don’t hurry If you don’t understand something, ask me.

3. Test #1 Useful Equations P 2  a 3 Kepler’s laws, including: Newton’s laws, including: F = ma F = G m 1 m 2 R 2 Gravitation: Speed of electromagnetic waves: c =  Energy = h  max energy  1T1T Wien’s Law: Stefan’s Law: L = A T 4 where the area A = 4  r 2 for a sphere

4. Radiation travels as waves. Waves carry information and energy. Review: Properties of a wave wavelength ( ) crest amplitude (A) velocity (v) trough is a distance, so its units are m, cm, or mm, etc. Period (T): time between crest (or trough) passages Frequency ( ): rate of passage of crests (or troughs),  Also, v =  1T1T (units: Hertz or cycles/sec)

5.  c = 1 nm = 10 -9 m, 1 Angstrom = 10 -10 m The Electromagnetic Spectrum

6. The frequency or wavelength of a wave depends on the relative motion of the source and the observer.

7. 1. Refraction Waves bend when they pass through material of different densities. swimming pool air water prism air glass Things that waves do

8. Kirchhoff's Laws 1. A hot, opaque solid, liquid or dense gas produces a continuous spectrum. 2. A transparent hot gas produces an emission line spectrum. 3. A transparent, cool gas absorbs wavelengths from a continuous spectrum, producing an absorption line spectrum.

9. Example: Blackbody - the microwave background Emits mostly in the radio, with a peak around 200 GHz

10. cold dusthotter star (Sun) “cool" star frequency increases, wavelength decreases Approximate black-body spectra of astronomical objects demonstrate Wien's Law and Stefan's Law very hot stars

11. Star wobbling due to gravity of planet causes small Doppler shift of its absorption lines. Amount of shift depends on velocity of wobble. Also know period of wobble. This is enough to constrain the mass and orbit of the planet.

12. initial gas and dust nebula dust grains grow by accreting gas, colliding and sticking continued growth of clumps of matter, producing planetesimals planetesimals collide and stick, enhanced by their gravity result is a few large planets Hubble observation of disk around young star with ring structure. Unseen planet sweeping out gap?

13. The Structure of the Solar System ~ 45 AU~ 5 AU L4 L5 L3

14. Oort Cloud is a postulated huge, roughly spherical reservoir of comets surrounding the Solar System. ~10 8 objects? Ejected planetesimals. A passing star may dislodge Oort cloud objects, plunging them into Solar System, where they become comets. If a Kuiper Belt object's orbit takes it close to, e.g., Neptune, its orbit may be changed and it may plunge towards the inner Solar System and become a comet.

15. Study hard and do well!