Nadir

The Nadir, in Latin imum coeli and commonly abbreviated IC, is the point opposite the Midheaven, where the ecliptic crosses the meridian below the horizon, and it is the cusp of the fourth house. Its significations are the foundations of a life: the home, the land, the family and its origins, the father in some schemes, ancestry, and in the classical texts the end of the matter, the outcome or the grave. The word nadir comes through medieval Latin from the Arabic nazir, opposite, and in strict astronomical usage it means the point directly beneath the observer, the opposite of the zenith, which is not the same thing as the IC; the astrological use of the word for the lower meridian is a loose one, and both terms are found. Like the other three angles it depends entirely on an exact time and place.

Because the Nadir is the exact opposite of the Midheaven, it inherits the same whole-sign-house complication discussed under that entry: in Hellenistic practice using whole-sign houses, the fourth-house cusp is not necessarily the Nadir's own degree but simply the fourth sign counted from the Ascendant, so that, as with the Midheaven and tenth house, the identification of the Nadir with a fixed fourth-house cusp is more characteristic of the quadrant house systems that came to dominate later Western practice than of the earliest surviving technique.

The Nadir, the Imum Coeli or lower meridian, is the point of the ecliptic exactly opposite the Midheaven. Like the Midheaven and unlike the ascendant and descendant, it is a function of sidereal time and the obliquity of the ecliptic alone: the geographic latitude does not enter the computation.

That is worth holding beside the ascendant. A chart of known time and unknown birthplace still has a meridian axis, because only the longitude is needed to fix the sidereal time, and it has no horizon axis at all. Everything an astrologer can say about the Midheaven and the Nadir in such a chart is on firmer ground than anything said about the ascendant, descendant or houses.

Its rate is the Midheaven's: one full circuit per sidereal day, advancing between about 0.92 and about 1.09 degrees of ecliptic longitude for every four minutes of clock time, the variation coming from the 23 degree 26 minute tilt between the ecliptic and the equator.

A terminological caution belongs here. In observational astronomy the nadir is the point directly beneath the observer's feet, the opposite of the zenith, and it has nothing to do with the meridian intersection of the ecliptic. The astrological Nadir and the astronomical nadir are different points and coincide only by accident. Where precision matters, the older term Imum Coeli, the bottom of the sky, is the unambiguous one.

In astrology this lower angle is the direct counterpart of the culminating Midheaven, sharing the same meridian axis but marking its lowest point rather than its highest, and the astrological term differs in a precise way from the strictly astronomical nadir, the point on the celestial sphere exactly opposite the zenith along the vertical circle through the observer, which need not fall on the ecliptic at all. Astrologers borrowed the everyday word "nadir" as a convenient label for the properly named Imum Coeli, the angle Hellenistic writers already tracked as the point opposite the midheaven even before the Latin cardo terminology was fixed by writers such as Firmicus Maternus in the fourth century.

Medieval astrologers working from Arabic sources, among them the tenth century astrologer al-Qabisi, known in Latin as Alcabitius, built widely used house division systems on this same meridian and horizon framework, and Alcabitius's approach became a standard of medieval European astrology for centuries. In chart notation this angle is abbreviated IC, from Imum Coeli, paired with MC for the Midheaven just as DC pairs with AC for the Descendant and Ascendant. On the standard circular wheel chart the IC sits at the bottom, directly beneath the Ascendant-Descendant horizon line, completing the four angle framework that has organized horoscopic astrology since its Hellenistic beginnings.