J. Xavier Prochaska
In simplest words, I count atoms and measure the ways that they move. This is the primary product of absorption-line analysis, a backwards approach to performing astrophysics. In short, we use bright background sources (quasars, gamma-ray bursts, etc.) to study gas in the foreground that reveals itself in silhouette. This allow us to study the nature of galaxies and the gas in between them in unprecedented detail.