Obviously, there are loads and loads
of web pages that study UFOs.
I'm not really going to dignify these
with any response. Suffice it to
say that there are lots of things
in the sky that are unidentified
that don't have to be aliens.
Birds, planes, meteors, and
reflections can all appear as
UFOs, and imaginations can create
UFOs where nothing is really seen.
Needless to say, there are lots of
people who work pretty hard to
show rationally that UFOs are really
just normal terrestrial activities that
we understand.
Philip Plait, who runs the
truly excellent web page
www.badastronomy.com,
has done some of this debunking.
One reason for people seeing UFOs,
he says, is
pareidolia, which is the phenomenon
of seeing familiar objects or patterns
in
an indistinct medium (like faces
in the clouds). Plait shows "Vladimir
Lenin in his shower curtain":
(Click
here if you don't
see the face.)
By the way,
Phil Plait's site has
excellent
movie reviews as well.