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Reference.org
Photosphere
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<p>The photosphere is a star's outer shell from which <a href="/facts/Light/jeofpMn4">light</a> is radiated. It extends into a star's surface until the <a href="/facts/Plasma_(physics)/1d3btMVU">plasma</a> becomes opaque, equivalent to an <a href="/facts/Optical_depth/XQwtIdFH">optical depth</a> of approximately 2⁄3, or equivalently, a depth from which 50% of light will escape without being scattered. </p><p>A photosphere is the region of a luminous object, usually a star, that is transparent to photons of certain <a href="/facts/Wavelength/kcJU0ymz">wavelengths</a>. </p><p>Stars, except <a href="/facts/Neutron_star/4enfoxBA">neutron stars</a>, have no solid or liquid surface. Therefore, the photosphere is typically used to describe the <a href="/facts/Sun/CadPCVHh">Sun</a>'s or another <a href="/facts/Star/PFbd6ICx">star</a>'s visual surface. </p>