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What is the Sun?

  Figure 2: A cut-away view of the Sun showing the convection zone, the photosphere, the chromosphere, many surface features and localized atmospheric eruptions like sunspots, flares and prominences. Courtesy of Gene Parker.

The Sun is a fairly average, middle-aged (some 4.5 billion years old) star which is currently composed of approximately 72% hydrogen, 26% helium and 2% of all other chemical elements (most notably those up to oxygen) in gaseous form. The source of the Sun's brightness (and that of other stars) is due to nuclear chemical reactions occurring in its innermost parts, where the temperature is 15,000,000 Kelvin (27,000,000F).

The Sun is 1,400,000 kilometers (900,000 miles) in diameter and liberates about 3.86 watts of energy from its surface. This energy, the solar luminosity, translates to about 1368 watts per square meter at the orbit of the Earth.


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Approved by Peter Fox
Last revised: Mon Apr 10 15:08:11 MDT 2000