The 33-cent stamp is part of the Postal Service's "Celebrate the Century" series, which commemorates events from each decade of the 20th century. The moon stamp is one of more than a dozen stamps commemorating the 1960s, along with topics such as "Super Bowl Kicks Off," "Vietnam War," and "Barbie Doll Steps Out." The moon stamp was unveiled today at the Kennedy Space Center.

Space is a recurrent theme of the "Celebrate the Century" series. The 1950s category includes a stamp for "U.S. Launches Satellites." The 1990s category, to be issued in April 2000, will include a stamp celebrating John Glenn's return to space.

Public voting has played a large role in determining which subjects are put on "Celebrate the Century" stamps. Ballots for each decade, distributed at post offices and online, have listed possible topics under categories such as "Arts & Entertainment" and "Science & Technology." The two top vote-getters in each category then become stamps.