Planetary Model

Niels Bohr, 1913 Rutherford's nucleus needed electrons — but where, exactly? Niels Bohr answered with an elegant (if imperfect) image: electrons orbiting the nucleus like planets around the sun, each locked to a fixed energy level. Jump between levels, emit light. The Planetary Model made atomic spectra calculable for the first time and became the most recognizable picture of the atom ever drawn. It was incomplete, but it was the first model to connect atomic structure to observable physics.