An Etymological Dictionary of Astronomy and Astrophysics

The time required for a photon created in the Sun’s core to attain the → photosphere and leave the Sun. If the photons were free to escape, they would take a time of only R/c (a couple of seconds) to reach the surface, where R is the Solar radius and c the speed of light. The solar material is, however, very opaque, so that photons travel only a short distance before interacting with other particles. Therefore, photons undergo a very large number of → random walks
before arriving at the surface by chance. The typical time is approximately
5 x 10⁴ years for a constant density Sun.

See also: → photon; → escape;
→ time.