Weakness file · 03

Red sun.

Under a red sun, he's only human.

Effect: He's effectively an ordinary man
Why: Red light doesn't recharge his cells
Rule set: Superman #141, November 1960
Krypton's sun: Rao

In brief

The short answer.

Under a red sun Superman loses his powers and is effectively an ordinary man. His powers come from yellow-sun energy stored in his cells, and red sunlight doesn't recharge them. The rule was set in 'Superman's Return to Krypton' in Superman #141 (November 1960), where Krypton's red sun, Rao, leaves him powerless.

Through the years

Era by era.

Golden Age (1938–1956)
No red-sun rule yet. Superman's powers are explained first by Kryptonian evolution and then by Earth's lower gravity.
Silver Age (1956–1970)
Supergirl's debut (1959) breaks the gravity idea, Action Comics #262 introduces 'ultra solar rays' from yellow stars, Superman #141 (1960) shows him powerless under Rao, and Superman #146 (1961) ties most powers to the yellow sun. Luthor traps him on a red-sun world in Superman #164 (1963).
Post-Crisis to today (1986–)
The solar battery idea: his cells store sunlight, so under a red sun he slowly runs down rather than switching off at once.
Animation
In Superman: The Animated Series, the villain Luminus turns Earth's sun red in the episode 'Solar Power'.

Try it

Yellow sun or red sun?

Power 100%

Under a yellow sun, like ours, his cells charge up and every power runs at full strength.

Under a red sun, like Krypton's, the charge drains away until he's as human as anyone.

The full file

The whole story.

A red sun is the one thing that can turn Superman into Clark Kent for real. It’s also the key to understanding all his powers, because it shows they were never really his: they’re borrowed from Earth’s sun.

Why does a red sun weaken Superman?

Superman’s powers run on yellow-sun energy stored in his Kryptonian cells. Red sunlight doesn’t charge them. Under a red sun his reserves drain away, and once they’re gone he’s effectively an ordinary man who can be hurt like anyone else. That’s the modern “solar battery” version DC itself describes.

Rao: Krypton’s red sun

Krypton orbited a red sun called Rao, which is why Kryptonians had no powers on their own world. For the planet and its people, see Krypton explained.

When was the red-sun rule introduced?

The red-sun rule arrived in the Silver Age, as DC replaced the old “Earth’s lower gravity” explanation:

Year	Story	What it added
1959	Supergirl’s debut, Action Comics #252	Argo City’s survivors had no powers there, which broke the gravity idea
1959–60	Action Comics #262	“Ultra solar rays” from yellow stars
1960	Superman #141, “Superman’s Return to Krypton”	Superman is powerless under Rao
1961	Superman #146	Most powers formally tied to the yellow sun
1963	Superman #164	Luthor fights him on a red-sun world

In short, between 1959 and 1961 the yellow sun became the source of Superman’s powers and the red sun became their off switch. Superman #141, by Jerry Siegel and Wayne Boring, is the story fans point to.

Red sun versus kryptonite and magic

Red sunlight removes Superman’s powers but doesn’t hurt him. Green kryptonite hurts him and can kill him, and magic gets past his defences while leaving his powers intact. See the ranked list on Superman’s weaknesses and where the powers come from on Superman’s powers.

Questions

Asked and answered.

Why does a red sun take Superman's powers?

Superman's powers come from Earth's yellow sun, whose energy his Kryptonian cells absorb and store like a battery. A red sun, such as Krypton's sun Rao, doesn't charge them. Once his stored energy runs out, Superman is effectively human and can be hurt like anyone else.

Did Superman have powers on Krypton?

No. Krypton orbited the red sun Rao, so Kryptonians had no powers at home. Superman #141 (November 1960), 'Superman's Return to Krypton', shows Superman powerless when he finds himself on Krypton, and that story made the red-sun rule part of the comics.

How do villains use red sunlight against Superman?

Villains trap Superman under red light to make him mortal. Lex Luthor fights him on a red-sun world in Superman #164 (1963), and in Superman: The Animated Series the villain Luminus turns Earth's sun red. Red-sun lamps and prisons are a recurring trick in the comics.