What is the name of the Sun's outer layer that we see as its surface?

The Sun’s outer layer that we see as its surface is the photosphere. It is the level from which most of the sunlight escaping toward Earth originates, so it forms the visible disk of the Sun.

The photosphere is not a solid surface. The Sun is a ball of plasma, and the photosphere is the depth at which the material becomes sufficiently opaque to visible light. It is roughly 100 to 400 kilometres thick, extremely thin compared with the Sun’s radius of about 696,000 kilometres.

Its visible texture includes granules, which are convection cells formed as hot plasma rises, spreads, cools, and sinks again. The photosphere also contains sunspots, darker and cooler regions created by intense magnetic fields. The average effective temperature of the photosphere is about 5,772 K.

The chromosphere lies above it, followed by the much hotter corona. A common mistake is to call the corona the Sun’s visible surface; the corona is the outer atmosphere and is normally too faint to see beside the bright photosphere.