Read this first! Start out by placing
the top edge of the image below at the
top edge of your monitor screen. It's a closeup of the surface of the
Saturnian moon Tethys, as imaged by
the Cassini-Huygens spacecraft. Note the heavily-cratered surface. Slowly
scroll down, admiring the craters, and notice
that at some point you will start seeing what appear to be boulders on
a rough surface, rather than craters.
If you now scroll back up, what looked like craters before now also
look like boulders. Most Web presentations
of this “crater/hill” illusion don't really work, for most viewers,
because of poor design
or concept. This real-life example works excellently. Try it! Can
you cause the flip from crater to boulder to occur by an act of
will? Try it!
![]() |
Illusion 1, Illusion 25, Illusion 50, Illusion 75, Illusion 110, Illusion 120, Illusion 130, Illusion 140, Illusion 150, Illusion 160, Illusion 170, Illusion 180