I

Iapetus

Saturn's third-largest moon, discovered by Cassini in 1671. There is some discussion as to whether this satellite is actually artificial – placed by an unknown race in the remote past – due to its very unusual features including an exceedingly dark leading hemisphere (possibly a coating) and a relatively bright trailing hemisphere; a very light density (is it hollow?); and the most striking thing: a giant ridge (13 km high) that goes right around it at the equator. Its two-tone effect has been photographed and looks impressively like the Yin/Yang symbol of the Tao. We shall have to wait until NASA sends another expedition to find the facts. In Greek mythology Iapetus was a Titan, the son of Uranus, the father of Prometheus and Atlas and an ancestor of the human race. Though fascinating, it has no known astrological significance. More about Iapetus [off site].

IAU

International Astronomical Union. The professional body for contemporary astronomers. No astrological significance.

Immersion

The beginning of an eclipse, or of an occultation. The opposite of Emersion, or coming out of the aspect.

Impedited

Debilitated, hindered, or damaged. A planet is impedited (impeded) in its natural action when afflicted, especially by malefics, or is in a general state of weakness due to position or lack of dignity. Particularly applies to the Moon, when afflicted by Sun, Mars or Saturn.

Imum Coeli (IC)

The fourth house cusp. The Lower Heaven, or Nadir. The north point of the horoscope.

Inconjunct

Widely used in recent times to refer to the quincunx, although the classical meaning is "not in mutual aspect". Neither semisextile nor quincunx are proper aspects in the traditional sense, as a planet is unable to "see" another in these relationships, unless it also beholds the other by virtue of being either antiscion or contra-antiscion (so not inconjunct). DeVore states that inconjunct means "dissociate" and that a planet is inconjunct when it forms no aspect and is not in parallel declination or mutual disposition to another planet, as well as being either quincunx or semisextile.

Increasing in Light

A planet increases in light as it progresses from the conjunction with the Sun to the opposition. Mainly used regarding the Moon.

Increasing in Motion

A planet moving faster than on the previous day.

Increasing in Number

Waxing. See "Increasing in Light".

Indifferents

Sun, Moon and Mercury, according to Henry Coley's Key to the Whole Art of Astrology (1676), are Indifferent, as opposed to Venus and Jupiter (Fortunes) or Mars and Saturn (Infortunes).

Inferior Planets

1. Traditionally, Sun, Moon, Mercury and Venus.
2. Planets orbiting between the Earth and the Sun (Moon, Mercury and Venus and the postulated Vulcan). The orbits of the superior planets, Pluto, Neptune, Uranus, Saturn, Jupiter and Mars (also the asteroids and trans-plutonian "planets" such as Trans-Pluto) lie beyond that of the Earth from the Sun.

Infortunes

Traditionally, Saturn and Mars. The Sun under some conditions, esp. in Vedic astrology. The Moon's South Node is an infortune, whilst Uranus and Pluto are malefic, so infortunes, though modern; Mercury and Neptune when afflicted. Ceres is almost certainly an infortune, according to current research. Several fixed stars, notably Caput Algol and Facies are distinctly malefic, therefore acting as infortunes.

Ingress

Entry of a planet into a sign. Usually the Sun's ingress into the four cardinal signs.

Intercepted

When a sign is fully enclosed between the cusps of a house without actually being on either cusp it is described as being intercepted. This only appears in charts; signs are never intercepted in the zodiac.

Interfector

Killing planet. See Anareta.