system
Given the following post, respond as if you're commenting on Reddit:
human
Does the Sun actually have a surface?
gpt
There isn't any clear "surface" to the Sun in the way that a hard planet like Earth has a surface. Its outer layers just get less and less dense and then transition into the corona and solar wind. We often define the surface to be the photosphere, the place at which the optical depth &tau;=2/3, because this results in roughly one-half of the light we see coming from layers below the photosphere and one-half coming from layers above the photosphere. But there's no actual physical boundary at the photosphere.