86
of his spectral classes. He observed stellar spectra visually, never photographically.
Thus, he described what he saw in 1868 as “kinds of rows of columns,” whose shadings diminished toward the blue end of the spectrum, not toward the red end as in
type 3 spectra.
7
In the 1870s, he identified a fifth class of line-emission stars such as
γ Cassiopeia (Fig. 5.4 and Table 5.1).
It is worth mentioning in passing that Secchi sometimes did miss important discoveries, such as the shift of spectral lines in stellar spectra compared to terrestrial
spectra. In March 1868 he reported to the Parisian Academy of Sciences a negative
outcome of a search for relative shifts among stellar spectral lines and laboratory
emission spectra.
8
William Huggins’s (1824–1910) observations 1 month later contradicted this finding. Using a high-resolution multi-prism spectroscope, Huggins
compared the position of strong lines such as Hb in the spectrum of bright stars like
7 See McCarthy 1950: 160, 1994. On Secchi’s late discovery of a fifth stellar spectrum class around
1870, first published in Secchi 1877, see Cenadelli 2005: 111–112.
8 See Secchi 1867: 979, 1868a: 375f. and 401: “for stars of the Sirius type there is, according to my
measurement instruments, no appreciable displacement.” Nevertheless, Secchi was among the first
astronomers to suggest to study Doppler shift of stellar spectral lines in order to detect radial
motions of stars (see Chinnici 2005).
Fig. 5.2 Stellar spectra observed by Secchi in 1863; on the top left, an illustration of Secchi’s
thermoheliometer (Ermolli and Ferrucci, Chap. 7, in this volume). From Secchi 1868d:
plate II, online at http://starlight.inaf.it/1871/12/analyses- spectrales- et- observations- desprotuberances- solaires/
K. Hentschel
of his spectral classes. He observed stellar spectra visually, never photographically.
Thus, he described what he saw in 1868 as “kinds of rows of columns,” whose shadings diminished toward the blue end of the spectrum, not toward the red end as in
type 3 spectra.
7
In the 1870s, he identified a fifth class of line-emission stars such as
γ Cassiopeia (Fig. 5.4 and Table 5.1).
It is worth mentioning in passing that Secchi sometimes did miss important discoveries, such as the shift of spectral lines in stellar spectra compared to terrestrial
spectra. In March 1868 he reported to the Parisian Academy of Sciences a negative
outcome of a search for relative shifts among stellar spectral lines and laboratory
emission spectra.
8
William Huggins’s (1824–1910) observations 1 month later contradicted this finding. Using a high-resolution multi-prism spectroscope, Huggins
compared the position of strong lines such as Hb in the spectrum of bright stars like
7 See McCarthy 1950: 160, 1994. On Secchi’s late discovery of a fifth stellar spectrum class around
1870, first published in Secchi 1877, see Cenadelli 2005: 111–112.
8 See Secchi 1867: 979, 1868a: 375f. and 401: “for stars of the Sirius type there is, according to my
measurement instruments, no appreciable displacement.” Nevertheless, Secchi was among the first
astronomers to suggest to study Doppler shift of stellar spectral lines in order to detect radial
motions of stars (see Chinnici 2005).
Fig. 5.2 Stellar spectra observed by Secchi in 1863; on the top left, an illustration of Secchi’s
thermoheliometer (Ermolli and Ferrucci, Chap. 7, in this volume). From Secchi 1868d:
plate II, online at http://starlight.inaf.it/1871/12/analyses- spectrales- et- observations- desprotuberances- solaires/
K. Hentschel