General Astronomy/The Photosphere

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The photosphere is the layer that we see when we look directly (foolishly) at the Sun. It is the sphere of light. It sometimes is referred to as the Sun's surface, but in fact the Sun has no solid surface such as that of the Earth. The photosphere merely represents the outer boundary of the region in which most solar energy has been converted into visible light.

Beneath the photosphere is the convective zone, a region in which huge columns of hot plasma rise and fall much like water boiling in a pot. On close inspection with properly filtered instruments, the photosphere appears as a great cauldron with the tops of these convective currents bubbling up in a seething sea. In certain wavelengths of light, the many convective columns give the Sun a slightly grainy appearance, sometimes referred to as granules or "rice grains," for its similarity to rice boiling in a pot.

Much cooler than the core of the Sun, the photosphere has a temperature of about 10,500 degrees F, or about 5800 K.

Immediately above the photosphere is a relatively thin layer called the chromosphere (sphere of color) and beyond that a large and very rarified outer atmosphere called the corona (crown). The photosphere is so vastly brighter than these two regions that they cannot be seen except with special instrumentation or during a total solar eclipse when the photosphere itself is blocked out.