A downloadable book explaining media oreilly.com -- Online Catalog::

The intro reads:

"We freeze some moments in time. Every culture has its frozen
moments, events so important and personal that they transcend
the normal flow of news.
Americans of a certain age, for example, know precisely
where they were and what they were doing when they learned
that President Franklin D. Roosevelt died. Another generation
has absolute clarity of John F. Kennedy’s assassination. And no
one who was older than a baby on September 11, 2001, will
ever forget hearing about, or seeing, airplanes exploding into
skyscrapers."