Sun and Continuous Spectrum
Name: John Y.
Why does sun light give continuous spectrum? Does the
source of sun light not originate from energy transfer between orbitals
of different energy level?
As you know, the nucleus of the Sun has a temperature
of about 15.000.000 Kelvin. Under such conditions, the
atoms hit each other and may fusion into other new and
heavier nucleus, in a thermo-nuclear reaction. During such
process, some mass is "lost" and - according to Einstein -
E=m.c^2 what means mass generate energy. Part of this
energy travels as electromagnetic waves, with all wave
lenghts, and that is why the spectrum of the sunlight is
continuous, from the nucleus. Furthermore, reaching the
sun surface, where the temperature is "lower", part of
this energy is absorbed by several elements that - in turn -
promote electrons to higher energy levels. And that is why
you get dark strips over the continuous sun spectrum
(the so called "Fraunhoffer Dark Lines").
The sun, obviously, is a hot body. Hot bodies emit radiation with a spectral
distribution given by the Planck formula -- so called black body radiation
that is continuous for all practical purposes. The radiation, in principle,
is discrete however the emissions are broadened by the pressure of the gases
comprising the Sun and the specific emissions are so close together and
numerous that they cannot be resolved experimentally.
There are discrete absorption lines in the solar spectrum due to absorptions
of specific wavelengths of cooler gases in the sun's outer atmosphere --
called Fraunhofer lines. The element helium was first discovered from its
absorptions in the solar spectra.
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Update: June 2012