An astrological age is a time period in astrological theory which astrologers say, parallels major changes in the development of Earth's inhabitants, particularly relating to culture, society, and politics. There are twelve astrological ages corresponding to the twelve zodiacal signs in western astrology. Advocates believe that when one cycle of the twelve astrological ages, called a Great Year, is completed, another cycle of twelve ages begins. The length of one cycle of twelve ages is 25,772 years. Some astrologers believe that during a given age, some events are directly caused or indirectly influenced by the astrological sign associated with that age, while other astrologers believe the different astrological ages do not influence events in any way. Astrologers do not agree upon exact dates for the beginning or ending of the ages, with given dates varying by hundreds of years. Overview There are three broad perspectives on the astrological ages: Archeoastronomers do not necessarily believe in astrology as a science, but rather study the cultural traditions of societies that did refer extensively to astrology. Astrologers have been interested in relating world history to the astrological ages since the late 19th century; however, most astrologers study horoscopes, not astrological ages. The pop-culture concept of the Age of Aquarius referring to major societal changes of the 1960s, popularized in the 1967 musical (and subsequent 1979 film) Hair. The following table of astrological ages was compiled by Neil Mann, and are based on typical durations cited for each era, as well as developments in human history typically cited as being influenced by the vernal equinox sign thereof. He notes that the supposed influences of the zodiac signs on human history are biased and rely on widely varying dates for the events cited, as well as selective cherry picking of evidence. Contentious aspects Definitive details on the astrological ages are lacking, and consequently most details available about the astrological ages are disputed. The 20th-century British astrologer Charles Carter stated that "It is probable that there is no branch of Astrology upon which more nonsense has been poured forth than the doctrine of the precession of the equinoxes." Neil Spencer in his 2000 book True as the Stars Above expressed a similar opinion about the astrological ages. Spencer characterizes the concept as being "fuzzy", "speculative", and the least-defined area of astrological lore. Derek and Julia Parker state that it is impossible to state the exact date