A photon's random walk JUN 27 2013
The Sun is so dense at its core that the average photon created by the fusion process takes more than 40,000 years to escape to the surface. !!!
The center of the Sun is extremely dense, and a photon can only travel a tiny distance before running into another hydrogen nucleus. It gets absorbed by that nucleus and the re-emitted in a random direction. If that direction is back towards the center of the Sun, the photon has lost ground! It will get re-absorbed, and then re-emitted, over and over, trillions of times.
This is from 1997, so that figure might have been revised a bit (anyone have updated numbers?) but still, that's incredible. (via hacker news)