If you think of a single atom as a grain of sand, then a wavelength of visible light—which is a thousand times larger than the atom’s width—is comparable to an ocean wave. The light wave can dwarf an atom, missing it entirely as it passes by. This gulf in size has long made it impossible for scientists to see and resolve individual atoms using optical microscopes alone.

Only recently have scientists found ways to break this “diffraction limit,” to see features that are smaller than the wavelength of light. With new techniques known as super-resolution microscopy, scientists can see down to the scale of a single molecule.

And yet, individual atoms have still been too small for optical microscopes —which are much simpler and less expensive than super-resolution techniques—to distinguish, until now.