The approximate 2150 years for each age corresponds to the average time it takes for the Vernal Equinox to move from one constellation of the zodiac into the next. This can be computed by dividing the Earth's 25,800 year gyroscopic precession period by twelve, the number of Zodiac constellations used by astrologers. According to different astrologers' calculations, approximated dates for entering the Age of Aquarius range from 1447 AD (Terry MacKinnell) to 3597 (John Addey). The start date for the Aquarian age is somewhat contentious and there is little uniform agreement upon the date or process leading from the previous Piscean age to the Aquarian age (or between any two ages). Nicholas Campion in The Book of World Horoscopes lists various references from mainly astrological sources for the start of the Age of Aquarius. Based on the research by Nicholas Campion most published material on the subject state that the Age of Aquarius arrived in the 20th century (29 claims), with the 24th century in second place with twelve claimants. Eight researchers claim the Aquarian age will arrive in the 25th century while the 21st, 26th and 27th centuries have seven supporters for each century. Other centuries that have a number of supporters for the beginning of the Aquarian age include: 22nd and 23rd centuries (6 each); 19th century (5); and the 18th century (4).Astrological ages exist as a result of precession of the equinoxes. The slow wobble of the Earth's spin axis on the celestial sphere is independent of the diurnal rotation of the Earth on its own axis and the annual revolution of the Earth around the Sun. Traditionally this 25,800 year cycle is calibrated for the purposes of determining astrological ages by the location of the Sun in one of the twelve Zodiac constellations at the vernal equinox, which corresponds to the moment the Sun rises above the celestial equator, marking the start of spring in the Northern hemisphere each year. Roughly every 2,150 years the sun's position at the time of the vernal equinox will have moved into a new zodiacal constellation. However zodiacal constellations are not uniform in size, leading some astrologers to believe that the corresponding ages should also vary in duration. This however is a contentious issue amongst astrologers.
In 1929, the International Astronomical Union defined the edges of the 88 official constellations. The edge established between Pisces and Aquarius technically locates the beginning of the Aquarian Age around the year 2600. Many astrologers dispute this approach because of the varying sizes of the zodiacal constellations and overlap between the zodiacal constellations.
Ages are believed by some astrologers to affect mankind while other astrologers believe the ages correlate to the rise and fall of mighty civilizations and cultural tendencies. Aquarius traditionally "rules" electricity, computers, flight, democracy, freedom, humanitarianism, idealists, modernization, astrology, nervous disorders, rebels and rebellion. Other keywords and ideas believed associated with Aquarius are nonconformity, philanthropy, veracity, perseverance, humanity and irresolution. The appearance or elevation in status of many of these Aquarian developments over the last few centuries is considered by many astrologers to indicate the proximity of the Aquarian age. There is no uniform agreement about the relationship of these recent Aquarian developments and the Age of Aquarius. Some astrologers believe that the influence of a New Age is experienced before it arrives because of a cuspal effect or Orb of Influence. Other astrologers believe the appearance of Aquarian developments, indicate the actual arrival of the Age of Aquarius.
