February 2, 2000

Oh, Be A Funny Geek, Kiss Me


 
"Two things fill my mind with ever increasing wonder and awe the more often and the more intensely the reflection dwells on them: the starry heavens above and the moral comprehension within me" 
   Carved on the gravestone of Emanual Kant, the 18th century philosopher.
 Read Chapter 23, chap 4.6-4.10. HW#1 Due Tommorow. HW#2 is now available.
First 10 minutes quiz: end of class on Friday. 1st question: What's your seat #.
Look it up by clicking here!

Observations:
Monday: Cloudy
Tuesday: First session some observations. Second cancelled.

Remember to check message, bring warm closthes. (See the blue members here...)

Reminder: The Doppler effect formula (also in lab #1) is:
Velocity of object / speed of the wave = (frequency change)/ stationary frequency 

Regarding what to learn for the exam and what to read: Since the notes do not follow the textbook religiously:

a. Regarding reading assignments: The minimum requirements are on the web page. The best results will be achieved by also reading the chapters in the syllabus.

b. There will be a help session on February 14 at 7:00pm in this room (hopefully). The exam coverage will be outlined in that session, and on the web.
 

1. "Black Body" radiation: 

Kirchoff laws: absorption lines, emission lines, "rainbows".

On BB: Emission lines bar-code & intensity graph, absorption lines bar-code & intensity graph.

Further discussion of "rainbows": 

Max. of intensity: 

Wien's Displacement law: 

Temperature =  289.8 x 10 4 nm Kelvin/ lmax.

0 Kelvin = - 273.15 Celsius.

Light with changing intensity demo: what happens to the spectrum? Hard to see because our eyes evolved to see in the visible! (redder - colder)

"Barcode" on Black Body (Rainbow spectra). 

Why do we have different spectra for different stars?

Spectrum is a result of Black Body emission partly absorbed by atomic transitions in atoms  in the way (as in Kirchoff rules from Jan 31).

Ionization of hydrogen (& other) atoms due to high temp in their outer layers prevents these atoms from absorbing the Black Body (rainbow) spectrum. Colder atoms: Photons excite more levels. Can be absorbed more easily.

Scheme of determining the stellar type: O0-9, B0-9, A0-9, F0-9, G0-9, K0-9, M0-9.
O0 - hottest
M9 - coldest 
 

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