131
In 1871, Secchi also analyzed the distribution of the prominences around the
solar disk and investigated the relation between the different solar regions. He made
use of the Merz telescope and the spectroscope usually employed to study the nature
of prominences. Secchi made the observations by positioning the slit of the spectroscope tangent to the edge of the solar disk image and then moving the slit parallel
and along the solar limb to fully explore the inner corona. By aligning the slit perpendicular to the solar limb, Secchi also compared the spectrum emitted by the
prominences with the photospheric spectrum.
The plates in Fig. 7.6 include drawings of the solar disk and inner corona and
various annotations. The drawings (Fig. 7.6a) show the solar regions observed in the
photosphere (spots, pores, faculae, and polar regions with an attenuated granular
structure) and in the chromosphere (prominences observed outside the solar limb).
The annotations describe the time and duration of the observations, the nature of the
observed regions, and their characteristics. A panel added in the lower part of the
plates (Fig. 7.6b) summarizes the data concerning position, shape, and dimensions
of the various prominences seen beyond the solar limb. In the added panel, together
with the observed prominences, it is easy to recognize the small-scale and rapidly
evolving jets of solar plasma protruding from the photosphere that are known today
as spicules and fibrils.
Indeed, thanks to his accurate solar spectroscopic observations, in 1877, Angelo
Secchi could identify spicules at the solar limb. These are very narrow and tall jets
of plasma in the solar atmosphere which have width of about 5000 km, lengths of
several thousands of kilometers, and lifetimes of only a few minutes. Secchi called
these features “burning fields” (“prateria ardente”).
Secchi noticed that prominences are not homogeneously distributed in the two
solar hemispheres and around the solar disk, they are mainly observed in the regions
between 10 and 40 degrees of latitude and are rare at the poles and at the equator.
Moreover, Secchi deduced from all this gathered evidence that the appearance of the
solar corona during eclipses “is closely connected with the prominences and
faculae.”
7.5 The Quest for Novel Instrumentation and Methods
In order to answer his scientific questions, Secchi developed novel instrumentation
to achieve higher spatial and spectral resolution observations of the solar atmosphere. In particular, he understood the need to resolve smaller spatial scales by
improving the instrumental characteristics and observational conditions. In fact,
while the aperture of the telescope determines its resolving power, the quality of
optical components and atmospheric seeing during the observations can affect the
quality of the observations. In addition to employing high-quality optical components, Secchi added regular annotations of seeing conditions during his observational work. He also developed a suite of tools to make it easy to observe the Sun
simultaneously in various ways.
7 The Legacy of Angelo Secchi at the Forefront of Solar Physics Research
In 1871, Secchi also analyzed the distribution of the prominences around the
solar disk and investigated the relation between the different solar regions. He made
use of the Merz telescope and the spectroscope usually employed to study the nature
of prominences. Secchi made the observations by positioning the slit of the spectroscope tangent to the edge of the solar disk image and then moving the slit parallel
and along the solar limb to fully explore the inner corona. By aligning the slit perpendicular to the solar limb, Secchi also compared the spectrum emitted by the
prominences with the photospheric spectrum.
The plates in Fig. 7.6 include drawings of the solar disk and inner corona and
various annotations. The drawings (Fig. 7.6a) show the solar regions observed in the
photosphere (spots, pores, faculae, and polar regions with an attenuated granular
structure) and in the chromosphere (prominences observed outside the solar limb).
The annotations describe the time and duration of the observations, the nature of the
observed regions, and their characteristics. A panel added in the lower part of the
plates (Fig. 7.6b) summarizes the data concerning position, shape, and dimensions
of the various prominences seen beyond the solar limb. In the added panel, together
with the observed prominences, it is easy to recognize the small-scale and rapidly
evolving jets of solar plasma protruding from the photosphere that are known today
as spicules and fibrils.
Indeed, thanks to his accurate solar spectroscopic observations, in 1877, Angelo
Secchi could identify spicules at the solar limb. These are very narrow and tall jets
of plasma in the solar atmosphere which have width of about 5000 km, lengths of
several thousands of kilometers, and lifetimes of only a few minutes. Secchi called
these features “burning fields” (“prateria ardente”).
Secchi noticed that prominences are not homogeneously distributed in the two
solar hemispheres and around the solar disk, they are mainly observed in the regions
between 10 and 40 degrees of latitude and are rare at the poles and at the equator.
Moreover, Secchi deduced from all this gathered evidence that the appearance of the
solar corona during eclipses “is closely connected with the prominences and
faculae.”
7.5 The Quest for Novel Instrumentation and Methods
In order to answer his scientific questions, Secchi developed novel instrumentation
to achieve higher spatial and spectral resolution observations of the solar atmosphere. In particular, he understood the need to resolve smaller spatial scales by
improving the instrumental characteristics and observational conditions. In fact,
while the aperture of the telescope determines its resolving power, the quality of
optical components and atmospheric seeing during the observations can affect the
quality of the observations. In addition to employing high-quality optical components, Secchi added regular annotations of seeing conditions during his observational work. He also developed a suite of tools to make it easy to observe the Sun
simultaneously in various ways.
7 The Legacy of Angelo Secchi at the Forefront of Solar Physics Research