Blackbody Radiation
Blackbodies - absorbs all the EM that strikes it
the intensity of each wavelength emitted is determined by its temperature
Wien’s Law - the dominant wavelength of EM emitted by a BB is inversely proportional to its temp.
l max = 2.9 x 10¯3 / T T in Kelvin
Stefan - Boltzmann Law - an object emits E at a rate proportional to the fourth power of its temp in Kelvins.
F = s T4
F is Energy Flux “rate of flow”
s = 5.67 x 10¯8
J/(m2•K4•s)
We can find the total E emitted (Luminosity) using
L = s T4
41r2
This allows us to compare stars (p.89)
Spectra
The solar spectrum contains fine dark lines called spectral
lines
Each Chemical element produces its own characteristic pattern of spectral lines
Spectroscope - optical device used to examine spectra when you photograph them - spectrographs
Kirchhoff’s Laws
1. A hot object or a hot, dense gas produces a continuous
spectrum - rainbow
2. A hot, rarefied gas produces an emission line spectrum - bright spectral lines against a black background
3. A cool gas in front of a continuous source of light produces an absorption line spectrum - a series of dark lines among a rainbow background.
So What Causes these spectral lines???
They are caused by electrons moving from energy level
to energy level
dark lines indicate absorption
bright lines indicate emission
The Doppler Shift or Officer I wasn’t speeding
D l/l = v/c
red vs blue shift -> not just a fashion statement anymore
radial vs. proper motion (OH)
Chp. 4 - # of 3