9
science was based on the studies of spectroscopy of Gustav Kirchhoff (1824–1887)
and Robert Bunsen (1811–1899), who had opened up the possibility of learning
about the physical and chemical nature of matter through the analysis of their light.
Langley himself contributed the invention of the bolometer, as well as being an
aviation pioneer.
Before that time, classical astronomy was limited to compiling catalogues of
celestial objects, the determination of orbits and the calculation of ephemerides
through the methods of celestial mechanics, and the studies of the shapes of such
celestial objects as nebulae and planets whose images could be resolved by telescopes. Astrophysics had a very different approach. To give a sense of the magnitude of this change, recall that in his Cours de la Philosophie Positive (1835),
Auguste Comte (1798–1857), the founder of Positivism, had categorically ruled out
the possibility of measuring the temperature and chemical composition of celestial
bodies. Less than 30 years later, Secchi’s publication of spectral classification would
pave the way for the chemical and temperature measurement of stellar atmospheres.
While the new approach struggled to establish itself elsewhere due to the misgivings of classical astronomers, who mainly had a geometrical approach toward
astronomy, in Italy the cultural climate was different (despite some criticism from
academics). Significant astrophysical research was able to be carried out there,
thanks to the ingenuity of Giovanni Battista Amici (1786–1863) and Giovan Battista
Donati (1826–1873), in Florence; Pietro Tacchini in Palermo; and Lorenzo Respighi
(1824–1889) and Secchi, in Rome.
Secchi approached astronomy essentially from the point of view of a physicist.
He did not ask where the celestial bodies were, but rather what they were. He was
among the first to grasp the importance of this new technique of spectroscopy for
the study of the Sun and the other stars:
… just when it seemed that the field of astronomical research had become barren, and that
the only thing left for us to do was to glean where others had richly reaped, behold a new
discovery has arrived that opens up an endless horizon that one day will reveal to us the
physical nature of the stars and thereby show us the kind of matter that composes them. This
is spectroscopy and its applications, as done by Kirchhoff and Bunsen. (Secchi 1865: 4)
While others had observed the spectra of a few bright stars, Secchi was the first
to observe thousands of such stars, recognize similarities among them, and begin to
classify them according to their spectra. Thanks to this pioneering work, Secchi is
rightly considered the father of the classification of stars based on their spectra, and
indeed among the founders of astrophysics itself.
Secchi obtained his spectroscopic observations with two achromatic refractor
telescopes: a Cauchoix 17 cm aperture telescope, which had long been in use at the
Observatory, and the Merz 24 cm aperture telescope, which had been purchased at
the time of the founding of the new astrophysical observatory. These instruments
could be equipped with Amici-type direct-vision prisms (Hoffman spectroscopes),
with a Merz objective prism or other spectroscopes designed by Secchi (Chinnici
2019), or similar to those in use in the chemistry and physics labs of the time. See
Chap. 8 for more details of his work in instrumentation (Figs. 1.3 and 1.4).
1 An Introduction to Angelo Secchi and his Collegio Romano Observatory
science was based on the studies of spectroscopy of Gustav Kirchhoff (1824–1887)
and Robert Bunsen (1811–1899), who had opened up the possibility of learning
about the physical and chemical nature of matter through the analysis of their light.
Langley himself contributed the invention of the bolometer, as well as being an
aviation pioneer.
Before that time, classical astronomy was limited to compiling catalogues of
celestial objects, the determination of orbits and the calculation of ephemerides
through the methods of celestial mechanics, and the studies of the shapes of such
celestial objects as nebulae and planets whose images could be resolved by telescopes. Astrophysics had a very different approach. To give a sense of the magnitude of this change, recall that in his Cours de la Philosophie Positive (1835),
Auguste Comte (1798–1857), the founder of Positivism, had categorically ruled out
the possibility of measuring the temperature and chemical composition of celestial
bodies. Less than 30 years later, Secchi’s publication of spectral classification would
pave the way for the chemical and temperature measurement of stellar atmospheres.
While the new approach struggled to establish itself elsewhere due to the misgivings of classical astronomers, who mainly had a geometrical approach toward
astronomy, in Italy the cultural climate was different (despite some criticism from
academics). Significant astrophysical research was able to be carried out there,
thanks to the ingenuity of Giovanni Battista Amici (1786–1863) and Giovan Battista
Donati (1826–1873), in Florence; Pietro Tacchini in Palermo; and Lorenzo Respighi
(1824–1889) and Secchi, in Rome.
Secchi approached astronomy essentially from the point of view of a physicist.
He did not ask where the celestial bodies were, but rather what they were. He was
among the first to grasp the importance of this new technique of spectroscopy for
the study of the Sun and the other stars:
… just when it seemed that the field of astronomical research had become barren, and that
the only thing left for us to do was to glean where others had richly reaped, behold a new
discovery has arrived that opens up an endless horizon that one day will reveal to us the
physical nature of the stars and thereby show us the kind of matter that composes them. This
is spectroscopy and its applications, as done by Kirchhoff and Bunsen. (Secchi 1865: 4)
While others had observed the spectra of a few bright stars, Secchi was the first
to observe thousands of such stars, recognize similarities among them, and begin to
classify them according to their spectra. Thanks to this pioneering work, Secchi is
rightly considered the father of the classification of stars based on their spectra, and
indeed among the founders of astrophysics itself.
Secchi obtained his spectroscopic observations with two achromatic refractor
telescopes: a Cauchoix 17 cm aperture telescope, which had long been in use at the
Observatory, and the Merz 24 cm aperture telescope, which had been purchased at
the time of the founding of the new astrophysical observatory. These instruments
could be equipped with Amici-type direct-vision prisms (Hoffman spectroscopes),
with a Merz objective prism or other spectroscopes designed by Secchi (Chinnici
2019), or similar to those in use in the chemistry and physics labs of the time. See
Chap. 8 for more details of his work in instrumentation (Figs. 1.3 and 1.4).
1 An Introduction to Angelo Secchi and his Collegio Romano Observatory