His main contributions was in the study of solar and stellar spectra.

The absorption lines in stellar spectra can be used to determine the chemical composition of the star.

Then, an absorption line at the given wavelength in a stellar spectrum shows that the element must be present.

By 1866, he had developed three classes of stellar spectra:

Note: The conventional color description takes into account only the peak of the stellar spectrum.

There he developed an interest in stellar spectra using photography.

Note: The conventional color description describe only the peak of the stellar spectrum.

First light raw frame of a stellar spectrum on the detector system screen.

His primary interest was the study of stellar spectra.

He took over a hundred more photographs of stellar spectra before his death in 1882.