Students who wish to understand the meaning of the phases "Piscean Age," and "Aquarian Age," which are so frequently bandied about with reference to historical eras, must be cognizant of the fact that two different zodiacs are involved, one of them moving and the other virtually stationary. These zodiacs turn against each other in a fashion somewhat analogous to the manner in which the subzodiac of houses appears to move in an opposite direction from the relatively fixed zodiac of the signs in a natal chart.

THE GREAT YEAR

It common knowledge that the day marks the period of the Earth's rotation upon its axis, while the year marks the period of its revolution around the Sun. However, many people to not realize that there is also a period of approximately 25,800 years known as the Great Year, during which the poles of the Earth's axis trace an imaginary circle in the sky.

This gyration of the Earth's poles occurs because our planet is an ellipsoid, flattened top and bottom and bulging at the equator. The gravitational pull of the Sun and Moon on the equatorial protuberance produces an oscillating movement similar to the wobble of a spinning top which tilts first one way and then another. Astronomers call this wobbling motion "nutation," a word derived from the Latin word nutare, meaning to nod.

Consequently, the Earth's axis is not always inclined in the same direction. About five thousand years ago, the North Pole pointed toward the star Alpha Draconis. By 2100 A.D., it will be pointing almost directly at Polaris, the present North Star. In the year 7500 A.D. Alpha Centei will be the Earth's polestar, and by 14,000 A.D., it will be Vega (Alpha Lyrae).

THE CELESTIAL EQUATOR AND THE ECLIPTIC

The celestial equatoris a projection of the Earth's equator upon the imaginary sphere of the heavens. Similarly, the extensions of the Earth's poles are called the north and south celestial poles. The ecliptic is the apparent path of the Sun through the heavens, and can be imagined as a line passing through the zodiacal constellations as they are seen at night. Since it is the Earth, and not the Sun, which moves, the ecliptic is really the plane of the Earth's orbit extended to meet the celestial sphere. The angle between the ecliptic and the celestial equator is called the obliquity of the ecliptic. At the present time, it measures nearly twenty-three degrees thirty minutes.

THE PRECESSION OF THE EQUINOXES

During the course of the year, the Sun appears to move slowly along the ecliptic to the left. When it reaches the point where the equator of the sky intersects the ecliptic, days and nights are of equal length. These points of intersection are called eqinoxes from the Latin equi, equal, and nox, night.

The spring, or vernal equinox, which occurs on or about the twenty-first of March, marks the point at which the Sun enters the sign (not the constellation) Aries. Before that time, it was seen in a position south of the celestial equator, and the nights were longer than the days in the Northern Hemisphere. After the passing of the Sun over the celestial equator for southerly to northerly declination, the days are longer than the nights.

Due to the Earth's nutation, the point at which the Sun passes the intersection of the ecliptic and the celestial equator is seen each year in a slightly different position against the background of stars. Thus, the signs which are measured from the equinox, gradually move away from the constellations, whose names they bear and which provide the unmoving sphere against which the vernal point shifts slowly backward. This retrograde movement is called the precession of the equinoxes.

In astrology, the thirty degrees of the ecliptic, known as the sign Aries, are always counted from the vernal equinox, even though year by year the slow retrograde motion of the equinoctial point along the ecliptic amounts to about fifty seconds of a degree, or a degree every seventy-two years. (This makes the normal human lifetime equal to one degree, or one day, of the Great Solar Year.) The vernal equinox marks a natural point of beginning, shown by the balancing of days and nights, whereas the constellations are arbitrary divisions of the heavenly sphere and no one is yet certain where they begin.

THE GREAT MONTHS

Just as the calendar year is divided into twelve months, the Great Year is divided into twelve time periods of approximately 2,150 years called Great Months. These subdivisions are measured from the point where it is presumed that the tropical and sidereal zodiacs originally coincided. The Great Months are named after the constellations even though they are actually eras of time, not areas of space. Some astrologers, including Dane Rudhyar, feel that the Great Months might more appropriately be called "phase one, phase two, phase three," etc., in order to avoid the confusion of applying the same names to different phenomena.

THE PRECESSIONAL EPOCHS

When the Greek astronomer Hipparchus discovered (or rediscovered) the phenonmenon of the precession of the equinoxes about 134 B.C., the signs and constellations, as we know them, virtually coincided. Now they have moved apart to the extent that the vernal point has gradually retrograded through the constellation Pisces and is entering the latter part of Aquarius. Simultaneously, the piousness of the Piscean past is giving way to the scientific detachment of Aquarius. Astrologers suspect that much of the turmoil of contemporary times stems from this transition.

The apparent existence of the great precessional ages is fundamentally mysterious. It implies that, regardless of its precise starting point, there is an enormous zodiac in the heavens which provides a frame of reference for the tropical zodiac of moving signs. How the ancients discovered this cosmic zodiac is so inexplicable, in the light of present knowledge, that one can only surmise that astrology is a "revealed" science rather than one which evolved naturally on this planet.