Photosphere

The photosphere is the outer layer of a star where light shines out. It reaches from the star's surface to where the hot gas, called plasma, becomes thick enough to see clearly. At this depth, about half of the light can escape.

Stars, including our Sun, do not have solid or liquid surfaces like Earth. Because of this, the photosphere is what we think of as the "surface" when we look at a star. It is from this layer that the light we see comes.

Etymology

The word photosphere comes from ancient Greek words. "Phos" means "light" and "sphaira" means "sphere". It describes a round surface that looks like it is giving off light.

Sun's photosphere

The Sun's photosphere is the outer layer that gives us its bright light. It is very hot, between 4,400 and 6,600 K, and looks very bright to our eyes. The photosphere is not a solid surface but a thin layer, about 100 to 400 kilometers thick, with a very low density.

Photospheric phenomena

Further information: Solar phenomena

In the Sun's photosphere, we see granules. These are like cells made of plasma. Each granule is about 1,000 km wide. Hot plasma rises in the middle, and cooler plasma sinks between them. They move very fast and only last about twenty minutes, making the Sun look like it is constantly boiling. There are also larger structures called supergranules. They can be up to 30,000 km wide and last up to 24 hours. They carry magnetic field bundles. Other magnetic features in the Sun's photosphere include sunspots and solar faculae.