For my Astrology A to Z series we have reached the Letter I [ i ]
The Imum Coeli is often simply referred to as the IC, it is one of the four Angles of the chart (the other three being the Ascendant [AC], the Descendant [DC] and the Mid Heaven [Medium Coeli or MC] )
The IC is located in the bottom part of your chart, near the middle, and it is exactly opposite from your MC at the top of your chart. The MC (Mid Heaven) represents a very public part of you - the part that is seen collectively by others and involves your participation with the public such as your career and social status. The IC (Imum Coeli) therefore represents the opposite; it is the part of you that is most private and hidden - it is how you behave when no one is watching.
The Imum Coeli represents the subconscious drives, it is a foundational part of our personality - often unseen or unknown even to us because it is a part of your core. I think of it like the internal organs . . . we SEE the outer part of our body so this is what we recognize and identify as "self", but we cannot SEE the internal organs, so we don't often identify ourselves with those. Nonetheless, they are a part of us and crucial to our daily functioning. Yet the IC is less about this hidden part of our physical bodies and more related to the hidden parts of the psyche.
The IC is therefore the most vulnerable part of ourselves, and the place where we are alone. Hellenistic astrologers considered the IC to be The Underworld, or Hades. It is the deepest hour of Night - if the sun is located near the IC you were born close to Midnight or in the middle of the night, hours before sunrise.
Using a quadrant-based House system such as Placidus or Porphyry, the IC will be the line that divides the 3rd house from the 4th House - it is the place where the 4th House begins. Therefore, the sign of your IC will also be the Ruler of your 4th House. The 4th House relates to our home life - therefore we see how the IC can represent who we are when we are alone. The MC is how we are perceived publicly - the faces we put on when we are outside the home. The IC is how we are when no one is around to see us. Yet we often don't give much conscious thought to this part of us!
The Imum Coeli can be a powerful tool for helping you do some Shadow Work*. By "Shadow Work" I mean the modern psychology practice described by Carl Jung; the process of seeing and integrating the hidden or unseen parts of yourself. It can be difficult to Identify with the traits of the IC - this is a part of our psyche we often hide from ourselves. It is also deeply connected to the Inner Child and our forgotten past; therefore, a wound or trauma that we do not wish to look at can be hidden here. The true function of Shadow Work as described by Carl Jung is to simply SEE these rejected parts of the self and accept them without judgement.
Examining the SIGN in which your IC resides is a great step in beginning the process of Shadow Work - which many people hear about but do not know where to start. If you have planets near the IC these may also hold clues to the Hidden parts of yourself, your Inner Child, and your subconscious.
The Imum Coeli - as ruler of the 4th House, can also teach us a great deal about what kind of nurturing we need, the type of home life we crave, and the basic structure of our innermost emotional world. It relates to our upbringing, our relationship with our parents, and even hold keys to how we can connect with our ancestral roots. As the point that is related to the Undwerworld and therefore our connection with our Ancestors, I believe that the IC can show us which of our ancestors we should work with in this lifetime - or what our Ancestors hope to teach us in this lifetime. As a suggestion if you have a practice that involves Ancestral work - study the meaning of the sign of your IC and have a conversation with your Ancestors about it - see how they respond!
Additional reading on the Imum Coeli:
*A note on Shadow Work:
The point of Shadow Work is to acknowledge a part of your subconscious that may be suppressed or rejected. We all have parts of ourselves that are "shadow" - a desire or instinct that we hide away from ourselves or the people around us. In Shadow work you acknowledge this part of yourself and accept it. This doesn't mean you have to behave in the manner of your shadow self, but it is simply bringing this part of yourself into your conscious awareness so that acting or not acting in this way is a conscious choice rather than a subconscious action. Some behaviors we suppress for good reason – maybe acting a certain way is destructive or harmful. But we should acknowledge that the urge to act in that way exists – therefore giving us more conscious control over that part of ourselves. There are other parts of our shadow that we were conditioned to suppress – perhaps we were told this part of us was bad or shameful as a child by our parents or a religious institution. In this case the suppression of the shadow might not be healthy, and we can decide as an autonomous adult whether to free that part of ourselves or not