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RAO - In the mythology of ancient Krypton, the sun-god, who was deemed the chief of all gods. So great was the respect for the red sun of Krypton that any soldier of Erok's time automatically became an officer if he had red hair. When Jaf-El preached the worship of the One god, he gave Him the name of Rao, though no longer identifying Him specifically with the sun. Note that in the wedding ceremony, the phrase used was "Rao, who kindled the sun," showing Him to be the sun's creator, but not the sun itself.
Link to definition above scanned from The Krypton Chronicles:
https://www.supermanthroughtheages.com/tales2/chronicles/3/?page=26Link showing Rao described as the sun god:
https://www.supermanthroughtheages.com/tales2/chronicles/3/?page=23In the time of Erok, who established the House of El, Rao was the sun.
While it's true that Superman tended to lose his powers under red suns and even blocking the yellow sun, it's inaccurate to say that it robbed him of all his powers in all cases. A Superboy story has his solar powers nullified by a yellow costume reflecting yellow sun rays but he retained his gravity-powers. A Metal Men team-up has his sun powers negated by I.Q.'s disrupting the sun so only his muscular powers -- not sun dependent -- remained (a DCCP story incl. Chemo).
When the Parasite stole Superman's holding back reflex so Kal's powers were escalating out of control, he reduced his powers to normal levels by coating his body with a chemical sunscreen that blocked out yellow sun rays and only allowed the red ones to reach his skin. He clearly had full command of all his powers in this case under artificial red solar conditions of his own making. It was only when the Parasite drained those remaining powers that Superman became totally powerless. (Ref: Superman #321 (March, 1978) "Too Strong to Survive" & Superman #322 (April 1978) "Laser War over Metropolis".)
The reverse was also true. High-gravity cables duplicating Krypton's gravity cut his powers by half when the Earth-2 Luthor used them on him in a team-up book with the Golden Age Superman (who's really the Earth-2 Superman as distinguished from the real GA Superman).