What defines the surface of the Sun?

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The Sun does not have a solid surface; instead, it has an apparent surface known as the photosphere. The concept of the photosphere relates to the mean free path of photons, which is the distance they can travel before being absorbed. Feynman's idea suggests that the 'surface' is where photons can escape the Sun's dense interior. This understanding clarifies the relationship between the Sun's appearance and the behavior of light within it. The discussion emphasizes the distinction between the Sun's actual structure and its perceived surface.
Hornbein
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The sun has no surface, but it appears to have a surface. I may recall that Feynman said that the apparent diameter is equal to the mean free path of a photon. That could be, but I don't get the relationship. Any help?
 
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Perhaps what Feynman meant is that the 'surface' is defined as the region where the mean free path of photons becomes large enough for most of them to leave the Sun without being absorbed?
 
Thread 'What is the pressure of trapped air inside this tube?'

Thread 'What is the pressure of trapped air inside this tube?'

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