The other end of the MC axis
Imum Coeli means the lower or deepest part of the sky. On a birth chart, the IC lies 180° from the MC along the ecliptic. If a recorded birth moment gives 14° Taurus MC, the IC is 14° Scorpio. That exact opposition is geometric, independent of how the chart’s houses are drawn. Calculate both degrees from a recorded birth time and birthplace longitude.
IC and nadir are different points
The nadir is the direction directly under an observer’s feet, opposite the zenith. The IC is where the lower half of the meridian intersects the ecliptic. Because the ecliptic is tilted, the IC generally does not equal the nadir. Calling the IC a “bottom of the chart” is a drawing convention, not an assertion that the zodiac point is exactly below the observer.
IC and the fourth house
Some quadrant systems use the IC as the fourth-house cusp, opposite a tenth-house-cusp MC. Equal House and Whole Sign can put the IC within a house instead. If two charts disagree over a fourth-house label while keeping the same birth time and longitude, check the selected house system before assuming one calculated a different IC.
Symbolic readings and birth time
Astrologers commonly associate the IC with private life, home, origins, and inherited patterns. These are interpretive themes, not demonstrated effects. The IC degree inherits the MC’s sensitivity to the birth clock and historical UTC offset. With only a birth date, there is no defensible exact natal IC sign or degree; use the date-only planetary chart without angles until a record supplies the time.