Summary Astronomy Rough Notes
Electromagnetic Spectrum, Spectral Types, Atoms and Spectra
Seven types of electromagnetic (EM) radiation
ROY G. BIV
 Long λ Short λ 
λ = 700 nm λ = 400 nm
 Low f
High f 
 Low energy High energy 
Radio
Microwave
Infrared
“feel”
video
Visible
Ultraviolet
camera
X-ray
Gamma ray
Slides - “Universe at all Wavelengths” or use Multiwavelength Astronomy Gallery
Multiwavelength Astronomy Gallery
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_astr
onomy/index.html
or http://sirtf.caltech.edu/EPO/Messier/gallery.html
or http://www.seds.org/messier
Why observe at all wavelengths?
1. Many sources don’t emit visible (want to see the entire universe - <10% visible).
Ex: Cool H (Radio)
New born stars (IR)
Black holes (X and gamma)
2. Can tell the energy of the process and maybe the process
Ex: 21 cm line  H spin flip  Locate H  Locate arms of the galaxy
3. Some wavelengths (primarily longer) penetrate better
Ex: Dust obscures galactic center in visible but not in radio
Astronomy Rough Notes – Types of Spectra
Types of Spectra (Continuous, Emission, Absorption)
Diffraction grating
Continuous spectrum
Demo with incandescent bulb
Describe: Rainbow like, All 
Source: Hot, dense object
Ex:
Filament of bulb, surface of sun (photosphere)
Emission spectrum
Demo with H gas tube (Note three lines: red, turquoise, violet)
Describe: Bright line
Source: Excited gas
Ex:
Gas discharge tube, gas clouds in outer space (Radio image of H in galaxy)
Demo with He gas tube (Note: different lines, must be a gas, not H)
Each element has a unique spectrum. Different gas has different spectrum.
Demo with Ne gas tube (Note: different lines, gas, not H nor He)
Absorption spectrum
Demo with camera/bulb/liquids
Describe: Dark line, Continuous with certain  missing
Source: Hot dense object shining through a cooler gas cloud/liquid
Sketch: source/gas cloud/observer
see text
Show solar spectrum
Absorption  hot dense photosphere with gas around
Show H lines
Note mix of lines/mix of elements
Use of spectra
Composition
Temperature
Density
Others
Astronomy Rough Notes – Atoms and Spectra
Play “The Ring of Truth” video, Part 6 “Doubt”
Show through Nancy Houck and classification scheme
Stop and review
Annie Cannon classified tens of thousands of stars
Classification scheme: (Hot) OBAFGKM (Cool)
Sub class 0-9 (zero – 9)
O,
B0, B1, B2,…B9, A0, A1, A2,…A9, F0…M9
(Oh) (B zero)
Why different lines? Why lines at all? Physics in late 1800s
Start video again. Play from Nancy Houck section through the quantum ladder.
Bohr Model of atom
Quantum ladder
Photon - tennis ball demo
Explains both emission and absorption spectra
Continue video from quantum ladder through Cecilia’s thesis
All that “glows” is 90% H and 10% He
Cecilia Payne (Established stellar temperature scale for stars, Figured out the recipe of the stars)