John Hearnshaw, Canterbury U, New Zealand

In this talk I discuss the origins of stellar spectroscopy in the 19thcentury. The story starts with Joseph Fraunhofer in 1814, who was the first person to describe the line spectra of bright stars. Surprisingly forty years followed before any major studies of stellar spectra were undertaken after Fraunhofer. The study of the solar spectrum by Gustav Kirchhoff and Robert Bunsen was a major impetus to apply the same techniques to stars. In the 1860s as many as seven observers initiated programmes in stellar spectroscopy. By far the most productive observers were Angelo Secchi in Rome and William Huggins in London, who each began their work in this new domain of research in December 1862. Whereas Secchi concentrated on spectral classification, Huggins mainly undertook line identifications to find which elements were present in the stars. However, both observers attempted to measure Doppler shifts in stellar spectra to record radial velocities. Both claimed positive results, but they were critical of each other’s work, and in the end, Secchi admitted defeat. In practice neither astronomer succeeded in this difficult task using visual spectra.

Secchi introduced his well-known stellar spectral classification in the years 1863 to 1868, and it was widely used in the astronomical community for about 50 years. In the end, the much more detailed classification schemes developed at Potsdam by Hermann Carl Vogel and at Harvard by Edward Pickering and his co-workers (especially Williamina Fleming and Annie Cannon), and for many more stars than observed by Secchi, resulted in the demise of Secchi’s classification scheme.

Secchi died young at the age of 59, leaving Huggins as the undisputed leader in stellar spectroscopy for the next two decades. During this time Huggins perfected the techniques of photographic stellar spectroscopy. These techniques were taken up at Potsdam by Vogel and at Harvard by Pickering, and they allowed reliable Doppler shift measurements to be made and hundreds of thousands of spectral classifications to be undertaken.