118
As Thomas Hockey has remarked (Hockey 1999a), the latitudinal asymmetry
that Secchi (1855) observed in Jupiter’s belts suggested that they might reveal
something about the nature of the giant planet. Another interesting point is that
Secchi observed two of the periodic episodes of reddening of the equatorial zone
(weakly in 1861 and strongly in 1869–70) which we now know form part of a
sequence of so-called global upheavals that occur from time to time. (Hockey 1999b).
Secchi has left us some of his portrayals of the cloud belts of Jupiter. Two drawings (of 1856 October 10 and 1857 December 6, with the latter showing the location
of the Red Spot Hollow) appeared in his famous book about the Sun (e.g., in the
French edition, Le Soleil (tome 2, 1877)). We can also find a contemporary reproduction of his detailed drawings of Jupiter in 1863 (Bakich 2000) that shows highly
irregular cloud belts. They are not dissimilar to the contemporary style of Charles
Piazzi Smyth (1819–1900).
6.6 Spectroscopic Studies
In 1867, both Secchi in Rome and William Huggins (1824–1910) in England
examined the spectrum of Mars. For Secchi this was merely part of a larger spectroscopic examination of the planets, and he also studied the gas giants (Secchi 1868
and 1872). He was interested in whether their spectra were simply that of reflected
sunlight or whether other features would show up. He could establish the presence
of absorption bands in the Martian spectrum and concluded from their low intensity
that its atmosphere must be comparatively thin and different in composition from
the atmospheres of the gas giants. To quote him precisely on the question of the
Martian atmosphere:
‘La sua atmosfera è assai piccola e sottile’. (Its atmosphere is very thin and subtle)
In 1863, Secchi had discovered absorption bands in the spectra of Jupiter and
Saturn, particularly towards the red end. These were not present in our own atmosphere (Secchi 1864; Alexander 1962e). This discovery, made in advance of the
parallel researches of Huggins in England, led Secchi to conclude that the atmospheres of the giant planets were ‘not yet cleansed’ (or primitive) compared to our
own; they contained as yet unknown gases.
In 1869, Secchi had been examining the spectrum of the variable star R
Geminorum when he turned his attention to Uranus, visible in the same field of the
finder, without expecting to see anything special (‘sans espérer y rien voir de particulier’) (Secchi 1869). He was surprised to see a bright spectrum, observed for the
first time, with a pronounced absorption band near one end (Fig. 6.6). The band was
roughly located in the green part of the visible spectrum near the solar line E; further
inspection revealed another dark band towards the violet, a considerable gap in the
yellow, with the red end of the spectrum very faint. Indeed, for Uranus and Neptune,
R. McKim and W. Sheehan
As Thomas Hockey has remarked (Hockey 1999a), the latitudinal asymmetry
that Secchi (1855) observed in Jupiter’s belts suggested that they might reveal
something about the nature of the giant planet. Another interesting point is that
Secchi observed two of the periodic episodes of reddening of the equatorial zone
(weakly in 1861 and strongly in 1869–70) which we now know form part of a
sequence of so-called global upheavals that occur from time to time. (Hockey 1999b).
Secchi has left us some of his portrayals of the cloud belts of Jupiter. Two drawings (of 1856 October 10 and 1857 December 6, with the latter showing the location
of the Red Spot Hollow) appeared in his famous book about the Sun (e.g., in the
French edition, Le Soleil (tome 2, 1877)). We can also find a contemporary reproduction of his detailed drawings of Jupiter in 1863 (Bakich 2000) that shows highly
irregular cloud belts. They are not dissimilar to the contemporary style of Charles
Piazzi Smyth (1819–1900).
6.6 Spectroscopic Studies
In 1867, both Secchi in Rome and William Huggins (1824–1910) in England
examined the spectrum of Mars. For Secchi this was merely part of a larger spectroscopic examination of the planets, and he also studied the gas giants (Secchi 1868
and 1872). He was interested in whether their spectra were simply that of reflected
sunlight or whether other features would show up. He could establish the presence
of absorption bands in the Martian spectrum and concluded from their low intensity
that its atmosphere must be comparatively thin and different in composition from
the atmospheres of the gas giants. To quote him precisely on the question of the
Martian atmosphere:
‘La sua atmosfera è assai piccola e sottile’. (Its atmosphere is very thin and subtle)
In 1863, Secchi had discovered absorption bands in the spectra of Jupiter and
Saturn, particularly towards the red end. These were not present in our own atmosphere (Secchi 1864; Alexander 1962e). This discovery, made in advance of the
parallel researches of Huggins in England, led Secchi to conclude that the atmospheres of the giant planets were ‘not yet cleansed’ (or primitive) compared to our
own; they contained as yet unknown gases.
In 1869, Secchi had been examining the spectrum of the variable star R
Geminorum when he turned his attention to Uranus, visible in the same field of the
finder, without expecting to see anything special (‘sans espérer y rien voir de particulier’) (Secchi 1869). He was surprised to see a bright spectrum, observed for the
first time, with a pronounced absorption band near one end (Fig. 6.6). The band was
roughly located in the green part of the visible spectrum near the solar line E; further
inspection revealed another dark band towards the violet, a considerable gap in the
yellow, with the red end of the spectrum very faint. Indeed, for Uranus and Neptune,
R. McKim and W. Sheehan