Over the course of the 1940s and 1950s, various alterations and additions to the makeup of Krypton were made in the comics. Among them was an explanation of why the natives of Krypton perished if they had possessed superpowers on their native world (as was the case in the earliest versions of Krypton outlined above, although this only became a problem once Superman — and by extension anyone from Krypton — was portrayed as increasingly powerful, able to withstand nuclear explosions, contrasted with his original power level in which a bursting mortar shell could penetrate his skin). Thus, it was explained by the early 1950s that Kryptonians were powerless on their own planet and would gain superpowers only within a lower gravity environment. This matched the correct theories being published that when man reaches the Moon (a lighter gravity environment) he will be able to lift great masses and leap great distances. In the early 1960s, added to this was the need to be exposed to the rays of a yellow sun (versus Krypton's red sun, Rao, which was older and cooler, or put out less energy) to gain superpowers, with the yellow sun aspect soon gaining the much greater emphasis. Other changes to the concept of Krypton and its culture were introduced, many of which were stylistic. Krypton in the Silver Age of Comic Books By the late 1950s, Krypton played an increasing role in various Superman stories, with greater detail provided about Krypton's makeup. Superman's Kryptonian heritage was a frequent factor in Silver Age Superman comic storylines, as he was fully aware of his origins from an early age. Superman would use this knowledge for such tasks as constructing advanced Kryptonian technology or observing some of Krypton's traditions. History Kryptonians made use of their advanced science to create a world where scientific inventions and research influenced much of daily life. Robots and computers were used for many tasks on Krypton, even for determining what career paths young Kryptonians would take as they grew up. Scientific and technological research were highly valued on Krypton, with the ruling body of Krypton named the "Science Council". Several stories featured characters traveling back in time to visit Krypton before its destruction; one example is the 1960 story "Superman's Return to Krypton", in which Superman is swept back in time to Krypton some years before its destruction. Powerless, he spends some time on