Photosphere
The photosphere is the surface of a star. It is located below the corona and chromosphere layers of a star's atmosphere.

In 2153, Vissians were able to travel well into the photosphere of G-type stars due to the trinesium hulls on their starships. At the time, flying into stars was not within the capacity of Starfleet ships. ()

The photosphere of a star could be masked out by the viewscreen of  starships such as the . In 2364, the crew of the Enterprise-D masked out the photosphere of a star in the Delos system in order to better study solar flares and magnetic activity occurring below. () 

In 2368, Kurn took the Hegh'ta into a star's corona and approached dangerously close to the photosphere before turning and going to warp in order to escape two other Klingon Birds-of-Prey chasing them. ()

After being towed into the interior of a Dyson sphere in 2369, auxiliary power needed to be diverted to the maneuvering thrusters so that the Enterprise-D could achieve a stable orbit outside of the photosphere of the star located inside the sphere. () 

In 2370, the Enterprise-D targeted the photosphere of a star with a particle beam in order to produce a solar fusion eruption that enveloped a Borg vessel. ()

External link 
 
 Astronomy