Although the Sun is gaseous, it can be seen only to the point at which the density is so high that the material is opaque. This layer, the visible surface of the Sun, is termed the photosphere. Light from father down reaches the Earth by repeated absorption and emission by the atoms, but the deepest layers cannot be seen directly. The surface is actually not sharp, but the Sun is so far away that the smallest distance that can be resolved with the best telescope is about 300 km (200 mi). Since the density e-folding height (scale height) is less than 200 km (120 mi), the edge appears sharp.
Although the Sun is gaseous, it can be seen only to the point at which the density is so high that the material is opaque. This layer, the visible surface of the Sun, is termed the photosphere. Light from father down reaches the Earth by repeated absorption and emission by the atoms, but the deepest layers cannot be seen directly. The surface is actually not sharp, but the Sun is so far away that the smallest distance that can be resolved with the best telescope is about 300 km (200 mi). Since the density e-folding height (scale height) is less than 200 km (120 mi), the edge appears sharp.