Orgasm pioneers, William H. Masters and Virginia Johnson.

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When gynecologist William H. Masters received official approval for his research project from Washington University in 1954, it was one of academia's closest-kept secrets at the time [source: Kolodny]. Masters even recruited a group of influential community leaders to help ward off any negative public reaction should his scholarly pursuits leak out. Sure, Alfred Kinsey had published "Sexual Behavior in the Human Female" the previous year, but the more hands-on tack Masters intended to take would've certainly ruffled moralistic feathers in that "Leave It to Beaver" era.

Over the next 12 years, Masters and his research assistant Virginia Johnson would analyze the sexual arousal patterns among 694 men and women. But instead of largely relying on self-reports of past experiences, Masters and Johnson were interested in the exact, real-time physiology of sex, which meant they needed to actually witness people in the throes of ecstasy. The duo filmed couples engaging in sexual intercourse, as well as individual participants masturbating, and simultaneously monitored the research subjects' blood flow and electrical activity in the brain [source: Severo]. To clarify what happens inside the mystifying vagina, Masters and Johnson even built a phallic device equipped with a tiny camera.

Compiling more than a decade's-worth of clinical research, Masters and Johnson outlined how men and women achieve sexual orgasms in their 1966 best-seller "Human Sexual Response." The revolutionary research helped pave the way for sexology as an accepted, credible discipline and is still a cornerstone of our collective knowledge about human sexual function.

But more than 50 years after that seminal publication, there's still a lot that isn't known about sex, and about orgasm specifically. In 2001, for instance, a pair of researchers from McGill University in Canada identified 26 different clinical descriptions for that coveted climax [source: Mah and Binik]. And though the crux of what an orgasm is -- a climactic, pleasurable sexual sensation -- is known, sex comprises only a sliver of the science behind the Big O.