From the book Ancient Egypt in Lace and Color.
The sun disk, carried across the sky each night by Ra - the Egyptian sun god.
Each day, Ra would carry the sun disk in his ship across the sky. And each night, the sun god had to travel through the underworld to return to the east. Apep knew which way Ra would have to travel in order to put the sun back into the sky. So every morning Apep would hide at the base of Bakhu the mountain of the horizon. Apep would try to defeat Ra to keep the sun from rising the next morning. If Apep succeeded, the world would be thrown into chaos. A few times, Apep did manage to swallow the sun boat, causing a solar eclipse, but inevitably Ra’s supporters would free the sun by cutting a hole in Apep’s belly and freeing the golden orb.