Page 91 - Intro to Space Sciences Spacecraft Applications

Introduction to Space Sciences and Spacecraft Applications
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RB - 1 solar radius

Figure 4-1. Solar regions. The sun’s characteristics change with distance
from its center.

to 30 days per rotation in the vicinity of the solar poles. The sun is com-
posed of six major regions as shown in Figure 4-1.

Core. The core is the region of the sun in which the conversion of mass
into energy occurs. Temperature in the core is about 15 x lo6 OK and the
density is about 110,000 kg/m3, conditions sufficient to cause the fusion
of hydrogen nuclei into helium nuclei with an associated release of ener-
gy. Approximately 4 billion kilograms of mass is converted into energy
every second, producing about 4 x kW of power. There is enough fuel
in the sun for this process to continue for at least a few billion more years,
so there’s no need to panic just yet.

Radiative Zone. In the region of the sun known as the radiative zone, the
energy produced in the core is transported slowly upwards by means of
absorption and reradiation of gamma rays, X-rays, and ultraviolet (UV)
photons from layer to layer.

Convective Zone. Through the convective zone, the major transportation
of energy is the convection (carrying) of energy by bubbles of hot gas that
boil their way up to the surface. Through a telescope, these bubbles can
be seen as a textured pattern on the sun called granulation. It is estimated
that the transport of the energy created in the core takes about 10 million
years to make its way through the radiation and convection zones to the
photosphere, where it is released to the solar system.