Journal of Astronomical History and Heritage, 11(2), 124 -133 (2008). 124 RADÓ KÖVESLIGETHY'S SPECTROSCOPIC WORK Lajos G. Balázs, Magda Vargha and Endre Zsoldos Konkoly Observatory, H-1525, Budapest, Box 67, Hungary E-mail: balazs@konkoly.hu, vargha@konkoly.hu, zsoldos@konkoly.hu Abstract: Kirchhoff and Bunsen's revolutionary discovery of spectral analysis in 1859 showed that observation of spectra made it possible to study the chemical composition of emitting bodies. Thermodynamics predicted the existence of black body radiation. The first successful spectral equation of black body radiation was the theory of continuous spectra of celestial bodies by Radó von Kövesligethy (published in 1885 in Hungarian, in 1890 in German). Kövesligethy made several assumptions on the matter-radiation interaction. Based on these assump- tions, he derived a spectral equation with the following properties: the spectral distribution of radiation depended only on the temperature, the total irradiated energy was finite (fifteen years before Planck!) and the wavelength of the intensity maximum was inversely proportional to the temperature (eight years before Wien!). Using his spectral equation, he estimated the temperature of several celestial bodies, including the Sun. As a byproduct he developed a theory of spectroscopic instruments. He presented a comprehensive discussion on the quantitative relationship between astrophysical spectra and the observer, equipped with some kind of instrument (telescope, spectrograph, detector, etc.). We briefly summarize his main results. Keywords: stellar spectra, spectral catalogues, spectral analysis, astrophysical instruments 1 KÖVESLIGETHY AND THE BIRTH OF ASTROPHYSICS Developments in physics during the nineteenth century produced a theoretically-coherent basis for the first attempts in modeling the internal structure of celestial bodies in terms of combining the equations of hydro- statics and the polytropic state (Arny, 1990; Lane, 1870; Ritter, 1882; Schuster, 1884; Schwarz 1992). In order to link these calculations to the emitted light, a theory describing the mechanism of emission was required: the interaction of radiation and matter. Two discoveries had fundamental significance in this re- spect. Firstly, Kirchhoff and Bunsen (1860) showed that there was a direct correspondence between the emission line spectrum of gases and the chemical constitution of the emitting source. In the second important discovery, Kirchhoff (1860) found that the wavelength dependence of the ratio e ()/a() = B() was a universal function where e () referred to the emission and a() to the absorption properties of the source at a given wavelength . In the case when a ()  1 (i.e. the source absorbs totally the incoming radiation), e ()  B(). Kirchhoff show- ed that the blackbody radiation, B(), depended only on the temperature of the source; however, he did not succeed in determining its functional form. During these exciting times professional astronomy was completely absent in Hungary. The Observatory on St. Gellért Hill had been destroyed in the siege of Buda in 1849 (Kelényi, 1930; Réthly, 1948). After the failure of the war of independence, the Austrian Government decided not to rebuild the Observatory (and the present-day Citadella can be seen in its place). The science of astronomy had no more luck at the University of Pest, where the first active professional astronomer, nominated as a Professor, was Radó von Kövesligethy in 1897 (Petrovay, 2006). Radó von Kövesligethy was a very interesting figure in the history of Hungarian astronomy. He was inter- ested in a wide variety of scientific subjects. Our aim in this paper is to present an overview of this spectro- scopic work. This work, though little known nowadays, produced some startling results. In his obituary by K. Oltay (1935) it is claimed that he discovered the same law for which Wien received the Nobel Prize in 1911. Looking through his book on theoretical spectroscopy (Kövesligethy, 1890), one is surprised to find his temperature radiation equation, which has a quite similar run to the one that Planck published fifteen years later and which provided the basis for modern quantum theory. Kövesligethy also gave a theoretical explanation for Balmer’s formula of the hydrogen lines. Figure 1: Miklós (Nicholas) Konkoly-Thege in the early 1930s (courtesy: Gothard Observatory, Szomathely).