The Photosphere - the "Surface" of the Sun
A full-disk view of the Sun, showing sunspots on the photosphere (top) and a close-up of solar granulation (bottom).
NASA/SDO and the AIA, EVE, and HMI science teams (left) and Royal Swedish Academy of Sciences - Oddbjorn Engvold, Jun Elin Wiik, Luc Rouppe van der Voort (right)
The photosphere is the visible "surface" of the Sun. The Sun is a giant ball of plasma (electrified gas), so it doesn't have a distinct, solid surface like Earth. Sunlight that is created by nuclear fusion in the Sun's core (center) gradually works it's way outward, colliding over and over with atoms in the Sun's interior. After a million-year journey, the sunlight finally reaches a level where the plasma is less dense and photons stop running into atoms and can finally escape into space. This level is what we see as the glowing "surface" of the Sun - the photosphere.
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