SP-402 A New Sun: The Solar Results
From Skylab
IMAGINARY SLICE cut from the ball of
the Sun lets us see all its known and suspected layers. In truth, no
one has ever seen beneath the photosphere. The Sun's prodigious
energy is believed to be generated by nuclear processes in the deep
interior of the Sun, in a dense, hot central core, about the size of
Jupiter, the largest planet. Core temperature is estimated to be
about 15 x 106 K: hot enough to trigger the process of atomic fusion
by which hydrogen, the Sun's abundant fuel, is converted to helium.
Energy released from this continuing process seeps outward through
the dense interior by radiation-the same
method that carries sunlight through the solar system. Near the solar
surface, the outward flow of energy becomes turbulent and unstable,
creating giant, rising bubbles of gas that make up the
convective zone. Finally, in a thin layer called the photosphere, the solar
energy that has worked its way to the surface at last becomes
visible-as the white ball of light we see each day with the naked
eye. To escape the Sun the light must still pass through three more
layers, each less dense than the ones before: the chromosphere, here
shown over the full disk of the Sun; the thin transition region; and
the ethereal, extended corona, largest of the
many masks of the Sun. Temperature in the Sun is hottest in the core,
and decreases slowly to the surface. At the photosphere the solar
temperature has dropped to about 6000 K. The temperature reaches a
minimum of about 4300 K in the low chromosphere, then rises rapidly
to more than 106 K in the lower corona. Waves carrying energy upward
from the convective zone probably release their energy in the
chromosphere, causing the abrupt temperature rise.
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