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5
Fundamentals of Solar Radiation*
Having been admonished by the Holy Ofce [the Inquisition] entirely to abandon the
false option that the Sun was the center of the universe and immovable, and that the
Earth was not the center of the same and that it moved … I abjure …
—Galileo
5.1 Physics of the Sun and Its Energy Transport
The nature of energy generation in the sun is still an unanswered question. Spectral
measurements have conrmed the presence of nearly all the known elements in the sun.
However, 80% of the sun is hydrogen and 19% helium. Therefore, the remaining 100-plus
observed elements make up only a ...