107
the other evenings particular drawings were made, and all these … were afterwards
harmonized together’. The resulting drawing was the most detailed made up to that
time, and revealed features, as English geologist John Phillips (1800–1874) wrote,
‘such as only the larger telescopes can command’ (Phillips 1856–1857).
Though an excellent observer, Secchi was not as talented in drawing and often
turned to his assistants to produce better sketches (Chinnici 2019). This limitation
probably inspired him to experiment with photography in 1856–1857, using wet
collodion plates, and led to the creation of the first lunar photographic atlas, containing eight plates of the different phases (Secchi 1858, 1859a; Chinnici 2019). Copies
were brought by Secchi to Paris and London and shown to the French Academy of
Sciences and to the Royal Astronomical Society.
In 1856, Secchi made his first observations of Mars, and 2 years later, at the
opposition of May 15, 1858, he and a Jesuit colleague, Father Enrico
Cappelletti (1831–1899), a skilled draftsman, would make a much closer study.
Secchi did not observe in 1860 – its declination was too far south – but other observations would follow. His reputation as a Mars observer primarily rests upon the
1858 results.
6.3 Mars in 1858
The year 1858 saw a fairly close approach of Mars to Earth, though it was not a
perihelic one because opposition did not occur within 90 degrees of the longitude of
perihelion (areocentric longitude (Ls) = 250°). Secchi and Cappelletti obtained an
impressive series of drawings of Mars from May 7 till August 14. The disk attained
18.0 arc seconds: still only about a fifth the diameter of the great lunar crater he had
needed six months to sketch! At opposition, Ls equalled 150 degrees: just after
midsummer in the north. Ls varied from 145 to 200°, up till early northern autumn.
At opposition on May 16, the planet’s declination was 19.6° south, making it
almost prohibitively low in the skies above England. But from Rome (latitude
41.9°), the planet passed the meridian at a more acceptable altitude of 28.5 degrees.
Things would deteriorate throughout August as the declination of the receding
planet became more southerly. The delicate pastels capture fugitive details from the
quivering telescopic images viewed against the darkening sky, above surrounding
heated rooftops and towers. The Collegio Romano observers were using their
244 mm (9-inch) Merz refractor with magnifications of x300–400. The drawings
were 42 mm in diameter.
Of those drawings that survive today, two sheets (covering the period June 3 till
August 14) are beautifully finished and executed in chalk pastel, probably upon a
light pencil sketch or outline (see Fig. 6.1a, b). The drawings represent a team effort,
but we know they were executed in their finished form by Cappelletti. Originally
preserved inside glass display frames at Collegio Romano, and after its closure at
the Rome Astronomical Observatory, fate has been somewhat unkind to this delicate
artwork, and many drawings have been affected by dampness and by black mould
6 Planetary Observations by Angelo Secchi
the other evenings particular drawings were made, and all these … were afterwards
harmonized together’. The resulting drawing was the most detailed made up to that
time, and revealed features, as English geologist John Phillips (1800–1874) wrote,
‘such as only the larger telescopes can command’ (Phillips 1856–1857).
Though an excellent observer, Secchi was not as talented in drawing and often
turned to his assistants to produce better sketches (Chinnici 2019). This limitation
probably inspired him to experiment with photography in 1856–1857, using wet
collodion plates, and led to the creation of the first lunar photographic atlas, containing eight plates of the different phases (Secchi 1858, 1859a; Chinnici 2019). Copies
were brought by Secchi to Paris and London and shown to the French Academy of
Sciences and to the Royal Astronomical Society.
In 1856, Secchi made his first observations of Mars, and 2 years later, at the
opposition of May 15, 1858, he and a Jesuit colleague, Father Enrico
Cappelletti (1831–1899), a skilled draftsman, would make a much closer study.
Secchi did not observe in 1860 – its declination was too far south – but other observations would follow. His reputation as a Mars observer primarily rests upon the
1858 results.
6.3 Mars in 1858
The year 1858 saw a fairly close approach of Mars to Earth, though it was not a
perihelic one because opposition did not occur within 90 degrees of the longitude of
perihelion (areocentric longitude (Ls) = 250°). Secchi and Cappelletti obtained an
impressive series of drawings of Mars from May 7 till August 14. The disk attained
18.0 arc seconds: still only about a fifth the diameter of the great lunar crater he had
needed six months to sketch! At opposition, Ls equalled 150 degrees: just after
midsummer in the north. Ls varied from 145 to 200°, up till early northern autumn.
At opposition on May 16, the planet’s declination was 19.6° south, making it
almost prohibitively low in the skies above England. But from Rome (latitude
41.9°), the planet passed the meridian at a more acceptable altitude of 28.5 degrees.
Things would deteriorate throughout August as the declination of the receding
planet became more southerly. The delicate pastels capture fugitive details from the
quivering telescopic images viewed against the darkening sky, above surrounding
heated rooftops and towers. The Collegio Romano observers were using their
244 mm (9-inch) Merz refractor with magnifications of x300–400. The drawings
were 42 mm in diameter.
Of those drawings that survive today, two sheets (covering the period June 3 till
August 14) are beautifully finished and executed in chalk pastel, probably upon a
light pencil sketch or outline (see Fig. 6.1a, b). The drawings represent a team effort,
but we know they were executed in their finished form by Cappelletti. Originally
preserved inside glass display frames at Collegio Romano, and after its closure at
the Rome Astronomical Observatory, fate has been somewhat unkind to this delicate
artwork, and many drawings have been affected by dampness and by black mould
6 Planetary Observations by Angelo Secchi