The visible surface layer of the Sun from which most of its light is emitted, appearing as the bright disk we see from Earth. This layer has a temperature of about 5,500°C and contains the granulation patterns and sunspots.
From Greek 'photos' meaning 'light' and 'sphaira' meaning 'sphere,' literally 'sphere of light.' The term was introduced in the 19th century as astronomers began to understand the Sun's layered structure and realized that what we see as the Sun's surface is actually a layer of gas.
The photosphere is like the Sun's skin - it's only about 500 kilometers thick, which is incredibly thin compared to the Sun's 1.4 million kilometer diameter, like the peel on an apple! What we think of as the Sun's solid surface is actually a layer of gas so dense that it becomes opaque, hiding the incredibly hot interior from our view.
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