G:

Geocentric: "earth-centered:" the model of the solar system before Copernicus and still used by many astrologers as a basis for interpretation.

Grand Cross: four planets in square aspect, including two oppositions (a complete fourth harmonic syndrome). This is an intense and often stressful structure needing a focus for it’s considerable energy into specific purposes and constructive action. Usually a grand cross occurs all in one quadruplicity: if in Cardinal signs, the outlet for the energy is action; in Fixed signs, the outlet is emotional and/or surrendering self-will; in Mutable signs, being able to see all sides leads to indecisiveness and diffusion of energy: an adjustment in thinking habits is necessary.

Grand Quintile: five planets all in quintile to each other, or 72° from each adjacent planet; also known as a fifth harmonic syndrome. Such horoscopes are quite rare, and are not well understood. It is more common to find incomplete fifth harmonic syndromes, in which three or four vertices of a pentagon in a horoscope are occupied by a planet.

Grand Sextile: six planets all in sextile to each other, or two interlocking grand trines, also known as a sixth harmonic syndrome. Such horoscopes are quite rare. Two more common and incomplete forms of sixth harmonic syndromes (that is, hexagons in a chart in which not every vertex is occupied by a planet) are kites and mystic rectangles, each missing two planets from a grand sextile.

Grand Trine: three planets each in trine to the other two; a complete third harmonic syndrome; perfect equilibrium and balance denoting great talent, ease or harmony, usually all in one element (earth, air, fire, or water); often a static, passive, inert structure not promoting the growth that confronting the problems of the hard aspects does - for this reason the ancients used to think of the Grand Trine as evil or malefic.

Gyroscope: a device invented in 1852 by the French experimental physicist Leon Foucault (1819-1868) as part of a two-pronged investigation of the rotation of the earth. The better-known demonstration of the Foucault pendulum showed that the plane of rotation of a freely swinging pendulum rotated with a period that depends on the latitude of its location. His gyroscope was a rapidly rotating disk with a heavy rim, mounted in low-friction gimbals. As the earth rotated beneath the gyroscope, it would maintain its orientation in space. This proved to be hard to do in practice because frictional forces brought the system to rest before the effect could be observed.