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Superman, a Kryptonian, flies toward the Earth's yellow sun to recharge his powers.

The Photonucleic Effect is the effect by which Kryptonians and creatures from the planet Krypton and, presumably, Daxam as well, are given incredible superpowers by exposure to Earth's Yellow sun.

The Photonucleic Effect was first explained in Elliot S! Maggin's novella, Starwinds Howl. It was explained as follows:

"The photonucleic effect is a very specialized astronomical phenomenon. It takes place when an object native to the influence of a red giant star enters the influence of a small G-type star. Every object in the Universe, organic or inorganic, has a distinctive signature based on the geological and cosmological characteristics of the environment in which it was formed. Rock from a planet whose gravitation is light would be less dense than rock of the same atomic structure, but from a world like Krypton whose gravitation is greater. Similarly, the musculature and cellular density of an animal born on one world must be different from that of the same species of animal born on another, or in deep space. The gravitation and magnetic fields acting on a creature during its growth necessarily define its eventual form as surely as does its genetic code. In fact, if twins with identical genetic codes were born in space, and one was raised on dense Krypton and the other on Earth, the one raised on Krypton would be far stronger than the one raised on Earth—assuming the Kryptonian twin survived at all. This is all, of course, no more than a thought experiment. It almost never happens.
Inorganic matter that originally formed in the orbit of a red giant like the star of Krypton almost never makes its way around interstellar space into the system of a yellow star. It is simply unlikely in the extreme. When, rarely, it does happen, it tends to develop an unstable and unpredictable radioactivity at the molecular level. Rocks spray off a steady stream of isotopic particles that may have unpredictable effects on their surroundings. A particle of the remainders of the world of Krypton might glow with what appears to be a rainbow light and its radiation could cause a plant to mutate irrationally. Organic exiles of a red giant star system are particularly susceptible to the inorganic radioactivity of elements with the same cosmological signature. But organic matter from the vicinity of a red giant—the living chemistry of plants and animals—has a wholly different response to yellow star-sun influence.

Superman at close proximity to Earth's yellow sun; how the star effects his eyes. An example of the photonucleic effect in action.

Where non-living matter becomes unstable and radioactive with this dislocation, living things develop an enhanced stability. The first thing that happens under the photonucleic effect is that the nucleus of each of an organic creature's cells grows a carapace—a temporary shell that shields it from external harm. This happens very quickly, from the outside of the organism - the cells in direct contact with yellow starlight—to the most internal cells of the organs, in less than the time it takes to draw a breath. For a moment, the organism is suspended in a comatose state, but the moment is too brief to notice. In that moment, the nucleus of every atom in the organism quakes. Each electron in every carbon or hydrogen atom in every molecule of its body jumps outward by one quantum level. The nucleus unbinds, its protons and neutrons and other subatomic particles loosening, expanding the binding space between them by the merest fraction of an angstrom. The molecules of the transplanted being's body do not actually grow, but the physical space that the solid parts of them take up thus increases exponentially without increasing the organism's actual mass or proportions. The organism becomes harder, tougher, more durable, better able to navigate the changed environment in which it now finds itself.
Perhaps something in the biology of those rare humans and canines and other chunks of biomass that were able to survive and eventually flourish in the vicious environmental soup of Krypton allowed for this response to such a displacement. Maybe it was simply a cosmic joke. Certainly the photonucleic effect was one of those delicious little bonuses built into the Universal circumstance back before that instant of Creation that Earthers call the Planck Epoch: the conception, under a supremely implausible nexus of events, of a theoretical super-being. This, against all likelihood, is what happened to the little dog Krypto."

It has also been learned that blue stars have an even greater Photonucleic effect upon Kryptonians, granting them exponentially increased powers, as well as the additional power of Superman Vision.

Physical Changes and Powers due to the Photonucleic Effect

Most of the amazing powers and abilities of Kryptonians under a Yellow Sun can be attributed to the photonucleic effect. These include:

  • Heat Vision - Kryptonians are able to release large amounts of the solar energy stored in their cells as heat (Presumably, as infra-red light) via their eyes in focused beams.
  • X-Ray Vision - Kryptonians have another vision power which allow them to use the energy in their cells to see through solid objects. This is presumably done by converting the energy in their cells into X-Rays.
  • Flight - The nature of this power is unknown, but it has been theorized that kryptonians can polarize their bodies magnetically against the Earth's magnetic field. Such an ability would certainly necessitate large amounts of solar energy in the cells.
  • Super-Speed - Kryptonians can, depending upon the amount of solar energy their body has stored up, move at incredible speeds. In some cases, close to or exceeding the speed of light, but this requires a HUGE amount of energy. Also, Kryptonians can perceive the world at this speed if they choose to, having seemingly-supernatural reaction time.
  • Super Strength - The muscles of a Kryptonian, because krypton's gravitational pull , can lift huge amounts of weight, far greater than their body mass.
  • Super Breath - Superman can freeze or just blow things with massive gusts of breath. It is unknown how the photonucleic effect causes this ability; presumably related to increased muscle strength and lung capacity.

Powers and Abilities Not Related to the Photonucleic Effect

It should be noted that it is possible that some superpowers might be available to Kryptonians and Daxamites even without the Photonucleic Effect.

Jor-El leaps up to his balcony from the ground, on Krypton. This feat could not be attributed to the Photonucleic Effect, as Jor-El was under a red sun, Rao, at the time.

In the earliest Superman comics, beginning with Action Comics #1, Superman had superpowers which seemed to merely be the result of the difference between Krypton's mass and Earth's. It was also sometimes explained as a result of the evolved and superior Kryptonian body- Kryptonians are said to have become a race of supermen. He had the following powers:

  • Invulnerability - Superman's body and cellular structure were greater due to the harsh environment and greater gravity of Krypton. He was able to handle anything up to a bursting shell.
  • Super Strength - Superman's muscles were naturally more resillient than that of a human, as they have to be to stand up on Krypton.
  • Super-Speed - Without the photonucleic effect, Superman was still able to run up to 30 miles per hour.
  • Leaping - Due to his strong muscles and his lighter body, superman was able to leap over a tall building or up to 1/8 of a mile.

However, it is possible that the photonucleic effect was acting on Superman at this point to some degree. It is shown that he is light enough to bounce over a building on Earth, however he's still able to walk as normal on the streets, like a human. This should not be possible; like an astronaut on the Moon, he should be bouncing around with every step. The photonucleic effect might allow him to remain stuck to the ground, by interacting with the Earth's magnetic field.

Possible Alternate Explanations

Other explanations for powers not covered in the photonucleic effect could include genetic engineering, biotech, and nanotechnology combined with advanced technology based around crystals as shown in Man of Steel (film) and Sunstone Crystal respectively.