like a rainbow
source: radiation from heat (like we discussed in the last lecture) from hot solids or hot dense gasses
|
Light: Spectroscopy and Atoms
text: Chapter 3, Sections 3.3 - 3.5
Sometimes we are interested in determining the composition of a star or the atmosphere of a planet. We can do that by studying the spectrum of light coming to us from these objects.
1. Continuous spectrum
like a rainbow
source: radiation from heat (like we discussed in the last lecture) from hot solids or hot dense gasses
2. Absorption line spectrum
dark lines in a continuous spectrum => light absorbed at certain wavelengths
source: cooler gas with a continuous source behind it
3. Emission line spectrum
bright lines at certain wavelengths (no continuous spectrum)
source: hot gas
Here is a link to a nice exercise discussing the various types of spectra.
line spectra will lead us to the structure of atoms
the orbits of electrons (and the spacing between them) can be treated like the rungs of a ladder.
absorption spectrum: If light with just the right amount of energy (wavelength, color) hits the atom, we can get the electron to jump to the next higher level. Only this color of light will be absorbed.
CD: Look under Astronomy Basics / Light and Atoms / Animations. The first choice whose description begins "Energy is released . . " describes atomic shells and light.
(2nd ed: See the Movie Gallery for Chapter 3: page 3 describes atomic shells, page 4 describes absorption of light.)
[Link to absorption animation]
emission spectrum: If an electron jumps down from a higher level to a lower level, light with a specific energy (wavelength) will be emitted.
Link to animation showing emission spectrum and atomic orbits.
The steps can have different sizes =>
different energies => different wavelengths (colors) absorbed or emitted
Each element has different spacings.
=> use pattern of absorption or emission lines to identify each element=> a fingerprint
oxygen:
helium:
Skip sections 3.6 and 3.7
Skip Chapter 4 on Telescopes
Previous Lecture - - - INDEX
OF LECTURES - - - Next
Lecture 
RETURN to Lecture Notes Outline
