Novae form a very interesting class of non-stationary objects. A considerable amount of observational data, both photometric and spectroscopic, covering different stages of nova outbursts, have been stored up by observers for many years. Processing and systematization of these data has lead to a better understanding of the physical processes taking place in the nova outbursts.
The first spectra of novae at maximum brightness proved to be similar to the spectra of supergiants; their distinctive feature was the presence of the strong lines of lines from C, N and O (McLaughlin, 1936). This fact lead to suspect that these elements must be overabundant in the nova envelopes.