What is Bohr's model of the atom?

The Bohr model can be found in the field of atomic physics. It described the atom as having a small, positively charged nucleus with negatively charged electrons moving in circular orbits around the nucleus. It introduced the concept of electrons occupying different levels in an attempt to explain the quantization of photons that are emitted from the atom when, for instance, an electron drops down from one orbital to a lower one.