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.