For the form of Bernoulli's equation given in Professor Pi's writeup, it's important to remember that *ρ g h* is only the gravitational potential energy in a uniform gravitational field, such as you might find in most engineering problems. In astrophysical problems it is usually the case that the gravitational field is nonuniform, in which case the *ρ g h* term must be replaced with the appropriate expression for the gravitational potential energy for the gravitational field in the problem. One particularly hairy case is the case of a self-gravitating fluid, in which the fluid itself has sufficient mass to contribute to the overall gravitational field. In that case, calculating the gravitational potential, using Poisson's Equation can be far more difficult than actually solving the fluid dynamics equations.