text: what is x-ray crystallography?   it is a way of using x-rays to see the structure of a crystal:  crystals are three dimensional ordered structures than can be described as a repetition of identical unit cells. the unit cell is made up of the smallest possible volume that when repeated, is representative of the entire crystal.   using visible light, it will never be possible to see atoms under even the most powerful of microscopes. in order for an object to be seen, its size needs to be at least half the wavelength of the light being used to see it. since visible light has a wavelength much longer that the distance between atoms it is useless to see molecules. in order to see molecules it is necessary to use a form of electromagnetic radiation with a wavelength on the order of bond lengths, such as x-rays.