Notes
Outline
The Interstellar Medium
Components of the ISM
Gas (hydrogen and helium)
Clouds
Molecular Clouds T~20K, n>1000/cc
Cold HI (neutral H) T~100K, n~20/cc
Warm HI T~5000K, n~0.1-1/cc
Diffuse gas
HII regions (ionized H) T~10000K, n~0.01-0.1/cc
Hot intercloud medium T~1 million K, n~0.001/cc
       (most of the volume)
Dust (silicates, graphites, ices)
Dark Clouds
Cirrus
HII regions
Red, White, and Blue  Nebulae
Scattering (and the blue sky)
Reflection Nebulae
Dark Clouds
Visible and Infrared Extinction
Emission, Extinction, Scattering, and Reddening
Kirchoff’s Laws
Emission and Absorption Spectra
Astro Quiz
The Milky Way
Discovery of the Galaxy
Shape of the Milky Way
Variable Stars –
A Standard Candle
The Shapley-Curtis Debate
Mapping the Galaxy : Radio Astronomy
Sources of Radio Emission -1
Sources of Radio Emission -2
Sources of Radio Emission – 21 cm radiation
Optical and Radio Sky
Spiral Arms in Galaxies
Density Waves
Tracers of Spiral Arms
Spiral Arms and Star Formation
Spiral Tracers from Outside
The Galactic Center
The Heart of the Galaxy
At the Core Lurks A Monster …
Stellar Populations
Galactic Structure
Formation of the Galaxy