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1.23: The Sun

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    • Contributed by Miracosta Oceanography 101
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    The Sun

    • By mass, the Sun is composed of hydrogen (70.6%) and helium (27.4%), all other elements are trace by comparison.
    • The Sun's average diameter is about 864,000 miles (about 109 times the size of Earth).
    • The Sun rotates on its axis in an unusual way. The rotation period at the Sun's equator is about 27 days, but is about 36 days at it poles.

    Figure 1.56. The Sun (our star), is one of billions of stars in our Milky Way Galaxy.

    Structure of the Sun

    The Sun's internal structure is inferred to be subdivided into several zones (Figure 1.54).

    • Core—The internal temperature of the Sun's is estimated to be about 27 million degrees Fahrenheit, hot enough to drive the nuclear fusion process of converting elemental hydrogen into helium, the source of solar energy.
    • Radiative zone—Above the core where fusion occurs, slowly radiates upward through the massive radiative zone.
    • Convection zone—The temperature is estimated to drop to about 3.5 million degrees Fahrenheit, where convection of "great bubbles of dense plasma (ionized matter) rise toward the surface in a convective manner (like a pot of boiling soup).
    • Photosphere—A 300 mile thick layer of hot gas makes up the surface of the Sun where most of the Sun's energy radiates into space. The Sun's surface temperature is about 10,000 degrees Fahrenheit, hot enough to radiate solar energy in the visible light spectrum.
    • Chromosphere and Corona—The outermost layer of the Sun is a thin solar atmosphere (the chromosphere) which extends as streaming plasma deep into space (the corona). The region is not a hot as the underlying photosphere, but is heavily influence by magnetic forces generated deeper in the Sun. Features of the chromosphere are only visible with special sun-observing telescopes. However, the corona is visible during solar eclipses when the disk of the Moon's shadow temporarily blocks the intense light form the photosphere (Figure 1.55).
    Internal structure of the Sun.
    Figure 1.57. Internal structure of the Sun.
    The Sun's corona is visible during a solar eclipse.
    Figure 1.58. The Sun's corona is visible during a solar eclipse.