  In this paper we revisited Hawking radiation in the light of the original
calculations of Hawking and Wald and found that some additional insights can be
gained. We review a "derivation" of the field theory Hilbert space from the
space of solutions, followed by the calculation of Bogoliubov coefficients in a
collapsed spacetime from first principles. We show that these calculations can
be generalized to the case of local Killing horizons and also to asymptotically
non-flat spaces.
