Diffraction  is a property of all waves and something that happens when a wave hits an object or passes through an aperture. 
This applies to waves in a pond, sound waves, or light waves 
- this gives CDs their amazing shiny culture 
- as  well as opals their textured shine 
- as well as atoms and molecules  
- the reason why nearby stars also have their distinct patterns


# Arago Spot 




# Frenel Zone Plate



When you shine light through a series of lines it becomes a working diffraction grating.