In Sophocles' play Oedipus the King, the peripeteia, anagnorisis, and catastrophe all occur at the same moment. When is this moment and who is...

A helpful discussion of the plot structure of
Oedipus Rex, which includes a useful chart, can be found here:
href="http://www2.cnr.edu/home/bmcmanus/oedipusplot.html">http://www2.cnr.edu/home/bmcmanus/oedipusplot.html
(see also the link below).  To summarize this discussion even more briefly: The
peripeteia occurs when the messenger, desiring to assist Oedipus,
reveals that the king and queen are actually his real parents – news that devastates
Oedipus. Anagnorisis occurs at this point, since Oedipus now
realizes his true identity. This realization leads to his
catastrophe.

What does this mean,
exactly?  The three italicized terms all come from Aristotle’s
Poetics and might be defined as
follows:

• Peripeteia
  is a sudden reversal or change, particularly of circumstances or situation. Ideally,
  everything in a good tragedy leads up to such a reversal, and everything that happens
  afterwards follows from that reversal. Often irony is involved in such a reversal, as it
  is in Oedipus
  Rex.


• Anagnorisis
  is a sudden recognition or realization, as in Oedipus’s abrupt discovery of the identity
  of his true parents and thus of his own identity as well. Oedipus thus also realizes
  that he has indeed killed his father and married his
  mother.


• Catastrophe is the
  tragic outcome (or at least the beginning of that outcome) of
  peripeteia and anagnorisis: the horrors that
  dominate the conclusion of Oedipus Rex are the direct results of
  the reversal and recognition Oedipus has just
  experienced.

Aristotle, who prized complex
unity in a tragedy, was especially impressed that Sophocles had managed to make the
reversal, recognition, and catastrophe in Oedipus Rex occur almost
simultaneously.  Doing so took great skill and design and produces a powerful impact
when the play is read or performed.

In one translation of
the play (see link below), the moment of reversal and recognition is rendered in these
words, spoken by Oedipus:

readability="13">

Ah me! ah me! all brought to pass, all
true!
O light, may I behold thee nevermore!
I stand a wretch, in
birth, in wedlock cursed,
A parricide, incestuously, triply
cursed!

Shortly following
this moment, Oedipus, after discovering that his mother has committed suicide, blinds
himself– a catastrophe if there ever was one.  No wonder that Aristotle considered
Oedipus Rex almost a perfect example and model of an ideal
tragedy.