He was a pioneer of astronomical photography. By photographing a total solar eclipse in 1860 he, and independently the English scientist Warren De la Rue (1815–89), settled the controversy over whether prominences belonged to the Sun or the Moon. Secchi also made the first classification of solar prominences into quiescent and eruptive types. He and W. Huggins were the first to approach astronomical spectroscopy systematically. Secchi made the first spectroscopic survey of stars, which yielded a catalogue of over 4000 spectra, published 1863. He suggested a spectral classification for stars (see secchi classification) from which the modern system of spectral types evolved.