Atum-Rà is the figuration of the sun god at the end of the day. A god who has aged and must regenerate by going through hardships during the night before return-ing in the early morning triumphant and magnificent in the form of Khepri.
This complicated journey takes place in a sacred boat that will be attacked by the great serpent Apophis, true brother and false friend, who will try to devour it to put an end to the eternal cycle.

The original meaning and the round shape reappeared among the Greeks, who were well acquainted with the Egyptian cults. Their Omega, Ω, is a semi-circle with horizontal lines, it is the symbol of the end, it evokes a horizon into which a disc would sink.
In Greek, the alpha and omega are thus the two ex-treme variants of a course. For the Egyptians, these were the points of appearance and disappearance of the sun god.