Re: Solar absorption lines
- From: William Hamblen <wrhamblen@xxxxxxxxxxx>
- Date: Sat, 08 Jul 2006 06:48:55 -0500
On Sat, 08 Jul 2006 20:22:50 +1000, Scott <ss@xxxxxxxxxxxxxxxx> wrote:
William Hamblen wrote:
On Sat, 08 Jul 2006 00:15:26 +1000, Scott <ss@xxxxxxxxxxxxxxxx> wrote:
But if I look at solar spectra, I don't see any significant
emission lines convolved with the continuum.
The emission lines are there.
Yes, but they are dominated by absorption lines. There is much more
absorption than emission.
The continuous spectrum is produced by
the photosphere and the lines are produced by the chromosphere.
I would like to understand how the chromosphere produces absorption lines.
When
there is an eclipse of the sun a spectroscope aimed at the limb of the
sun will show a flash spectrum of emission lines in that brief period
of time when the moon hides the photosphere but exposes the
chromosphere. The emission lines are at the same wavelengths as the
absorption lines.
I'm not sure what you mean by "flash spectrum". Are you refering to
solar flares? (which cause emission lines to be convolved with the
standard solar spectrum)
The light emitted by a hot, dense substance forms a continuous
spectrum. The region of the sun that is made of a hot plasma and
emits a continuous spectrum is the photosphere. When light passes
through a thin, ionized gas selected wavelengths are absorbed in
narrow bands. Thin, ionized gases also emit light. The spectrum is
not continuous but consists of specific wavelengths that depend on the
chemical element involved and the degree of ionization. Each element
has a characteristic spectrum and for a given element the absorption
lines and emission lines are at the same wavelength. This was
discovered in the laboratory in the 19th century and made it possible
to identify the elements in the outer parts of the sun. The outer
region of the sun that is made of a thin, ionized gas, and produces
the numerous, narrow black lines visible in the spectrum of the sun,
is the chromosphere. During a solar eclipse the chromosphere is
visible to the eye as a red line at the edge of the sun. When the
chromosphere, but not the photosphere, is briefly visible during the
eclipse the flash spectrum consists of emission lines that are at the
same wavelengths as the absorption lines usually visible in the solar
spectrum. It is called the flash spectrum because it is visible only
as a brief flash during the eclipse. You could do a Google images
search for "flash spectrum" to see examples on the world wide web.
An electron absorbs and emits radiation at wavelengths depending the
changes in energy of the electron. Electrons in atoms can have only
certain energies. Because of this, under the right conditions, you
see emission or absorption lines in the spectrum. Calculating the
energies and wavelengths in a spectrum is part of modern physics.
Read some basic books on astronomy and physics. One of the
astronomy-for-non-science-majors texts such as George O. Abell's
Exploration of the Universe is a good choice for the astronomy book.
Consult a dictionary for the meaning of convolve while you are at it.
Bud
.
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