This chapter describes how large-scale structure -- the distribution of galaxies on the sky -- can be used to probe the cosmological model. We start by defining the density perturbation and its most fundamental statistical property -- the correlation function. We briefly review the evolution of density perturbations in the standard cosmological model, emphasizing key results. We next discuss the growth of cosmic structure, and segue into talking about the power spectrum of density perturbations, its theoretical description, and its measurements. This leads us to discuss structure formation in the universe more generally, the role of numerical (N-body) simulations, and the mass function. We end by discussing how the statistical properties of dark-matter halos, which can easily be modeled in simulations, are related to those of galaxies that we typically observe.

In Chapter 4, we look at nonresonant scattering, specifically Rayleigh and Raman scattering from linear molecules. We continue with the semiclassical (quantum) treatment, leading to the induced dipole moment and associated differential scattering cross section. Explicitly adding vibrational and rotational manifolds of the ground state, we show the results for all three regimes: Rayleigh, rotational Raman, and vibrational Raman scattering. We then apply these results to nitrogen and oxygen molecules and associate the results with macroscopic quantities, such as the index of refraction of an ensemble, or gas. From this point, we focus specifically on Rayleigh + vibrational Raman spectra of O2 and N2, determining vibrational and rotational constants and the thermal populations of the states, based on their molecular energies, which leads to the spectral strengths of individual lines. We finish this chapter with a description of the Cabannes spectrum and the effect of the density fluctuations on its lineshape, considering the success of theoretical models in reproducing these spectra in Knudson (low-density), kinetic (medium-density) and hydrodynamic (high-density) regimes.