'Light' - Some of the amazingly detailed things a few photons can tell us about the universe, by analysing spectra.
The areas discussed include:
What is a Photon? | The electro-magnetic spectrum |
How are Photons Produced? | Atomic transitions (bound-bound and bound-free); free-free transitions; Opacity of Earth's atmosphere |
The Sun - Absorption Spectrum | Black body radiation; spectral lines; use of hydrogen alpha |
Emission Spectrum | Dust cloud nebulae; Fluorescent lights |
Doppler Effect - Red Shift | Spectral broadening from temperature; Active galactic nuclei (AGN) broad line velocity broadening |
What is 'z'? | Red shift; v/c for low velocities; relativistic rules for high velocities |
Estimating the Density of a Cloud | Comparing line strengths of closely related meta-stable lines |
Estimating the Temperature of a Cloud | Similar trick to estimating density, with transitions that have temperature dependence |
Lyman Alpha and the Lyman Alpha Forest | Assessing the structure of the inter-galactic medium (IGM) |
Lyman Alpha and More Cosmology | The Gunn-Peterson trough; When the universe became neutral and then became re-ionised; Cosmic microwave background (CMB) radiation |