  A number of properties of dense matter can be understood semiquantitatively
in terms of simple physical arguments. We begin with the outer parts of neutron
stars, and consider the density at which pressure ionization occurs, the
density at which electrons become relativistic, the density at which neutrons
drip out of nuclei, and the size of the equilibrium nucleus in dense matter.
Subsequently, we treat the so-called "pasta" phases expected to occur at
densities just below the density at which the transition from the crust to the
liquid core of a neutron star occurs. We then consider aspects of superfluidity
in dense matter. Estimates of pairing gaps in homogeneous nuclear matter are
given, and the effect of the dense medium on the interaction between nucleons
is described. Finally, we turn to superfluidity in the crust of neutron stars
and especially the neutron superfluid density, an important quantity in the
theory of sudden speedups of the rotation rate of some pulsars.

Nuclear Theory;High Energy Astrophysical Phenomena;Other Condensed Matter