Atomic spectroscopy was a well-developed and highly active research area in the years up to 1913, where Niels Bohr published his famous trilogy on the structure of atoms and molecules. It lived its own life with surveying and empirically systematisation of spectral lines from flames and electrical discharges into gases; But nobody knew how the characteristic spectral lines of the basic substances are actually formed.
This changed completely with Bohr's atomic model. There was a very fruitful interplay between theory and experiment, as theoretical predictions were immediately verified empirically, and new experimental discoveries continually challenged the new theory formations.
Atomic spectroscopy is still a living area of research, but it has changed its character many times in its long life, albeit steadily since 1913 has been characterized by strong and fruitful links between theory and experiment. This was illustrated very clearly by this year's dispensation of the Nobel Prize in Physics, which went to groundbreaking works within modern spectroscopy. Among these are the development of the most accurate time meters in the form of optical atomic clocks, which are based on specific spectral lines in atomic ions.