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is viewed. The blue portion of the solar spectrum is strongly scattered by the atmosphere, which is why the sky looks blue. Viewed straight on, our sun appears yellow because the atmosphere is also more absorptive toward the blue end of the spectrum, except at dawn or sunset when the position of the sun is low on the horizon and sunlight must travel a greater distance through the atmosphere. Nearly all wavelengths are then absorbed, except for lower-energy red light, which gives sunsets their characteristic hues (the greater number of particulates in the air at the end of the day compared with the beginning also contributes to the difference in shading between sunset and dawn). These spectral features are for the most part independent of the chemical composition of the gases making up the Earth’s atmosphere. There is no physical mechanism by which a shift in the primary wavelength of sunlight from yellow (a wavelength of 570 nanometers, or 570 billionths of a meter) to red light (650 nanometers) would endow someone with the ability to bend steel in his bare hands. Consequently, at this stage in his history, Superman ceased being a science-fiction strip and became a comic book about a fantasy hero. Changing a superhero’s origin in order to accommodate new powers or circumstances occurs so frequently in comic books that comic-book fans have coined a term, “retconning,” to describe this retroactive continuity repair.
    Interestingly, Superman’s foes went through a similar evolution around this same time. In the early years of Action and Superman comics, Siegel and Shuster gave voice to the revenge fantasies of their young and economically disadvantaged Depression-era readers. Superman first used his powers to fight corrupt slum-lords, coal-mine owners, munitions manufacturers, and Washington lobbyists. In his very first story, he psychologically tormented a lobbyist by holding him as they both fell from a tall building. At this early stage of his career, the story lines indicated that only a few people knew of Superman’s existence, and the lobbyist believed that the fall would be fatal. He willingly divulged the information Superman was after rather than risk another such fall. In the 1940s and 1950s, in addition to selling millions of comics per month, Superman had become a star of radio serials, movie shorts (both animated and live action), and a popular television program. His adversaries subsequently morphed into criminal masterminds with colorful personas and costumes, such as the Toyman, the Prankster, and Lex Luthor, whose schemes for grand larceny or world domination Superman would foil while keeping the corporate power structure safely undisturbed. As befits the escalating capabilities of the villains he faced, Superman entered a superpower arms race, eventually growing so powerful that it became difficult for writers to concoct credible threats to challenge his godlike abilities. Radioactive fragments of his home planet, known as Kryptonite, became a frequent device to extend any given story beyond the first page of the comic. 9
    It is the simpler, original Superman of the Golden Age, the last son of Krypton, that I wish to consider here.

THE PHYSICS OF JUMPING AND ALL OTHER MOTION
    In the first years of his comic-book history, Superman was unable to fly but could simply “leap tall buildings in a single bound,” thanks to Earth’s weaker gravity.
    Well, how high could he leap? According to his origin story in Superman # 1 , Superman’s range was given as one-eighth of a mile, or 660 feet. Assuming he could jump this high straight up, this is approximately equivalent to the height of a thirty- to forty-story building, which in 1938 would have been considered quite tall. So our question can be rephrased as: What initial velocity would Superman need, lifting off from the sidewalk, to vertically rise 660 feet?
    Whether we wish to describe the trajectory of a leaping Man of Steel or of the tossed ball from