Glossary
I
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, Y, Z

IC—See Imum Coeli.
Impeded Planet—A badly aspected planet. Mars, Saturn, Uranus, and Pluto are often involved.
Imum Coeli—IC. On the cusp of the Fourth House, opposite the medium coeli (MC). See also Medium Coeli.
Inconjunct Aspect—Now mostly used in reference to a quincunx aspect. Originating as derogatory for certain aspects not considered to be major.
Inferior Planets—These are Mercury and Venus, located between the Earth and the Sun. They travel very quickly and influence rapid change.
Ingress—A planet entering the sign of the zodiac.
Inner Planets—See Inferior Planets.
Intercepted Sign—A sign is intercepted when it lies wholly within a single house and does not occupy the cusp at either end of the house. A planet is intercepted when it lies in an intercepted sign. Being intercepted may restrict the freedom of the planet to act.
Invariable Plane—The central plane of the solar system. It passes through the solar system's centre of mass and makes an angle of about 1°35´ to the Earth's plane of orbit.