a sphere of light or radiance.
Astronomy. the luminous visible surface of the sun, being a shallow layer of strongly ionized gases.

1655–65; photo- + -sphere

photospheric [foh-tuh-sfer-ik, -sfeer-] , adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
photosphere (ˈfəʊtəʊˌsfɪə)
the visible surface of the sun, several hundred kilometres thick

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
photosphere   (fō'tə-sfîr')  Pronunciation Key 
The lowest visible layer of a star, lying beneath the chromosphere and the corona. Stars are made entirely of gas and thus have no surface per se, but the gas beneath the photosphere is opaque, so the photosphere acts as their effective visible surface; it is also the boundary from which the Sun's diameter is measured. The Sun's photosphere is a very thin layer made up of numerous granules (transient convective cells) where hot gases rise and give off light and heat. The photosphere of the Sun has a temperature of around 6,000°K and is the region in which sunspot activity is located.
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Example sentences
These particles came from the sun's visible surface, called the photosphere.
The sunspots are darker, deeper, and cooler than the photosphere.
The photosphere is the visible surface of the sun and the lowest layer of the
The center does not radiate in space so it is irrelevant, likewise everything
  below the photosphere.
Image for Photosphere
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