Diffraction pattern without a slit A few weeks ago, I aimed a laser at a wire perpendicular and interestingly, I saw the diffraction pattern, like the picture below:

Why is this happening? I mean, I don't have any slits and I'm aiming the laser at a wire but why is a diffraction pattern is seen on the screen
Can you please draw how the waves are diffracted?
 A: Some of the light is blocked by the wire.  But the light passing immediately off the upper and lower edges of the wire's silhouette act as two point sources, which interfere with each other when they reach the screen behind the wire.
Babinet's principle says that the diffraction pattern from the edges of an opaque body is the same as that from the edges of a hole or slit of the same size.  The reasoning behind this is that if you have two complementary screens, one opaque exactly where the other is transparent, then the radiation patterns of light passing through each screen must sum to the radiation pattern of the light when it is unobstructed by either screen.  In order for this to be true, the patterns of each screen must be of the same amplitude but of opposite phase.
Here's a description of how to use diffraction around a wire to determine the thickness of the wire: http://www.optics.rochester.edu/workgroups/berger/EDay/EDay2008_Diffraction.pdf.  Here is another account which shows how the light at the edges of the wire acts as two point sources: http://physicsed.buffalostate.edu/pubs/StudentIndepStudy/EURP09/Young/Young.html.
