The Solar Eclipse 1999 From Hungary
EurAstro Team Szeged I (Manfred Rudolf, Alfred Jakoblich, Franz Michlmayer, Carmen Ortega)
Solar spectra obtained during the eclipse
On the following pictures you can see spectra of the Sun taken at different phases of the eclipse.
On the left of the spectrum there is a picture of the phase when the spectrum was
recorded: diamond ring, chromosphere, corona. The three spectra look quite different:
Diamond ring:
A continuum spectrum of the photosphere, some bright emission lines of the chromosphere are already visible.
In the continuum, very fine dark lines are visible, particularly in the green and blue part of the spectrum (Fraunhofer absorption lines).
Spectrum of the chromosphere:
Some seconds after the second contact, and some seconds before the
third contact, the chromosphere is visible. The chromosphere is a rather thin (ca. 5000 km)
atmospheric layer of the Sun (The pink-coloured region on the left-hand side of the solar image).
The composition and temperature of the chromosphere are comparable to that of the photosphere, however the density
of the chromosphere is far less than that of the photosphere. Therefore the continuum spectrum changes to an emission spectrum, where the
emission lines correspond to the absorption lines in the continuum spectrum, although some other lines are visible.
Since the bright emission lines of the chromosphere are are visible for several seconds only, and appear rather suddenly, the chromospheric spectrum is also called "Flash spectrum".
The bright lines in red and turquoise, and two of the blue lines correspond to hydrogen, whereas the yellow line is indicative of helium.
Helium was first discovered in 1868 by its yellow emission line in the flash spectrum recorded during a solar eclipse.
The wavelength of the emission lines is indicative of the composition (chemical elements) while the intensity of the lines
reflects the abundance of the elements (ca. 70% hydrogen, 28% helium, the rest heavier elements).
See the emission lines of: Hydrogen (656, 486, 434, 410 nm; indicated by white lines), Helium (587 nm (white line), 502, 447 nm),
Sodium (589 nm, close to the yellow helium line), Magnesium (516, 517, 518 nm), Calcium (397, 393 nm).
Many of the green lines are due to the presence of iron.
Coronal spectrum
The corona is the extremely tenuous outer part of the Sun's atmosphere which attains temperatures of up to several million kelvin and
extends many million kms into the interplanetary space. A spectrum of the inner corona is shown below:
In the spectrum you can distinguish a red, yellow, a faint green, turquoise, and several blue circles. Each of them represents an image
of the solar corona in a different wavelength. The red, turquoise, and some of the blue images again are
due to the hydrogen emissions, and the yellow image corresponds to helium.
The bright dots on the circumference of the solar images represent the prominences.
The green emission at a wavelength of 530 nm was first discovered at an eclipse in 1869. An emission line at that wavelength was unknown in
laboratory spectra, and a new element was suspected, named "coronium". Later it turned out that
this green emission was due to iron atoms from which 13 electrons have been stripped off (FeXIV), and
which can only be found under the extreme conditions of the corona at temperatures of
2,000,000 Kelvin or higher. This also makes clear why there are no green "dots" (images of prominences) on the circumference of the green solar image.
The temperature of the prominences is about 4000-6000 K only and thus far too low to allow the formation of the highly ionized FeXIV.
In the image below the emission lines of the flash spectrum have been straightened by "bending" the image along a curve. So the assignment of
the spectral lines is considerably simplified.
Some prominent emission lines are:
Hydrogen: Ha (657nm),
H b (486 nm),
Hg (434 nm),
Hd (410 nm)
He I: 668, 588, 502, 492, 447 nm
Ba II: 650, 614, 493, 455 nm
Na I: 589 nm
Mg I: 553, 516-518 nm ("triplet")
Sr II: 422, 408 nm
Ca I: 586, 423 nm
Ca II: 397,393 nm
Fe I: many lines between 520-570 and 413-430 nm
The spectra have been recorded with a 2" spectroscopic grating (200 grooves/mm) which was mounted in front of a 500 mm telephoto lens.
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