photosphere


pho·to·sphere

noun \ˈfō-tə-ˌsfir\

Definition of PHOTOSPHERE

1
:  a sphere of light or radiance
2
:  the luminous surface layer of the sun or a star
pho·to·spher·ic \ˌfō-tə-ˈsfir-ik, -ˈsfer-\ adjective

First Known Use of PHOTOSPHERE

1664

photosphere

noun    (Concise Encyclopedia)

Visible surface of the Sun, about 250 mi (400 km) thick. It emits most of the Sun's light that reaches Earth directly. Temperatures range from about 18,000 °F (10,000 °C) at the bottom to 8,000 °F (4,000 °C) at the top; its density is about 1/1,000 that of air at the surface of Earth. Sunspots are photospheric phenomena. The photosphere has a granular structure. Each grain (cell), a mass of hot gas several hundred miles in diameter, rises from inside the Sun, radiates energy, and sinks back within minutes to be replaced by others in a constantly changing pattern.

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