Ketu, the opposite node to Rahu, came into being during the churning of the Ocean of Milk. The last gift of that churning was the emergence of the God of Healing, Dhanvantari, with the pot of amrit, the nectar of immortality. Ketu and Rahu were whole at that time, in the form of a demon known as Swarbharnu, who engaged in subterfuge to obtain the nectar whilst it was being served out by the enchantress Mohini. The deception was discovered by the Sun and Moon, who ran tale-telling to the great God Maha Vishnu, who promptly sent his discus and separated the head from the body; the body is today known as Lord Ketu, South Node of the Moon.
Ketu has very poor reputation garnered over the ages and in narrative, yet, is disposer of intelligence of a deep order. Ketu is also disposer of Spiritual Intelligence.
Aspects of Ketu
Ketu, the Vedic deity and navagraha sans head, has a dark body, smoky in colour with flecks of green. As Ketu behaves and takes characteristics from Mars (with whom Ketu is enemy), Ketu shares the Pita dosha with Mars, being fiery in nature. Of the nakshatras, Ketu is Lord of Ashwini - the first nakshatra, rajasic (energetic) in nature and auspices dharma, right action. In Mahga nakshatra, Ketu is once again rajasic in nature and here, seeks artha, wealth. In Moola, the 21st nakshatra, Ketu is also rajasic in nature and here, has the goal of kama, desire.
It is important to note these nakshatras, for each marks the first in distinct divisions of the nakshatras and divisions (called pada). Ketu marks the birth of the conscious mind in Ashwini, the forward development of conscience in Mahga and the drive to supreme consciousness in Moola.
Ketu is a lesser malefic than his opposite, Rahu. Ketu is friendly towards Rahu and Venus, neutral toward Sun, Jupiter, Mercury and Saturn, andenemies with Mars and the Moon (causes lunar eclipses). Ketu is exalted in Scorpio, debilitated in Taurus, shares House Lordship with Mercury in the sixth house, rules the south-west with Rahu and has digbala (extra strength) in the 12th house. In the astrological chart, Ketu (and Rahu) always move in reverse order, backwards with respect to the motion of the other planets.
Conjunctions of planets with Ketu are said to be eclipses of that planet. As the nodes and their activity of causing eclipses causes blockages of light from the Sun and planets, they are points of transformation of energy. We must remember that the planets are forces which disperse the light they reflect from the Sun. When this reflected light is blocked, there is shadow. When the shadow passes, there is light again. Which transformed aspect of the seven rays has been exposed to the light, brought out into the light of day? We must ask ourselves about this transformation, change. It is the function of the nodes, Rahu and Ketu, to reveal hidden forces, strength and energy through their activity.
Divinity, Light, Deity
Light comes from the Central Sun of all the Worlds - all the Universes, to the Sun of our own solar system in this galaxy. That light is then reflected by the planets in a process of combining and recombining light as vibration, force, energy and thus, creating inner change around the souls, the hearts and minds of men, women and children. This world is light, this solar system is light, this galaxy is light, this universe is light, all is light in separation (maya or illusion) from the One Light which the soul is a spark of.
We may name this uncreated, self-effulgent light the Creative Source of All, Self-effulgent, Divine, God, Purusha (the universe is the body of the formless Divine), and with many other names. Divinity, in any other word. All planets are expressions of the One form, the Purusha, and thus, reflect divine energy. Each of the planets are divine forces and it is their task to raise us up to the Divine itself. Ketu is one of the Gods, and the Divine auspicing Ketu are Brahma, the creator-god, and Rudra, the terrible aspect of the God who is the receiver of all things.
Ketu and Spiritual Intelligence
It is said that Rahu and Ketu form the celestial army (BHPS). Rahu pushes back the frontiers while Ketu maintains the home territories. It is here, in the home territory, the inner space within that Ketu delves deep with wide range and capacity for inner exploration, self awareness and concentration. Ketu is said to be karaka - disposer of jnana - wisdom, and in this aspect gives deep intelligence and deep concentration. All intelligence is problem solving skill.
There are several elements of spirituality - such as mystical experiences, transcendence, sanctification, spirituality as problem solving skill and spirituality as ethical and virtuous behaviour. These are the components of spiritual intelligence.
I'd like to take a moment to raise a distinction between religion and spirituality. Religion is an institution with organised beliefs. Spirituality, on other hand, is an experience.
Spirituality doesn't require you to believe anything. Rather, spirituality constantly invites you to notice your experience. Your personal experience becomes your authority rather than something someone else has told you.
Spiritual practice imparts an awareness within you to what will bring you peace, and what will not bring peace. Yet, frequently, spiritual progress disturbs peace. This is one of the principal functions of Ketu in the spiritual dimension, to disturb peace by bursting the bunds, the inner spiritual boundaries with interaction with the divine, revelation of the divine, in the outer world through activity. Ketu has the function of exposing us to new realities, reality which is imbued and filled by the Divine, both immanent (within everything) and transcendent (beyond and in all at the same time).
The Celestial Army, the Inward Battle
We said earlier that Rahu and Ketu form the celestial army. It is the purpose of an army to provide protection and defence of the community, through formation and discipline. To carry the metaphor further, military discipline takes raw recruits, drills them, exposes them to heretofore unknown skills, abilities, experiences, environments and pressures all with stringent discipline in preparation to providing that protection and defence. Ketu does the same; after acquisition personal habits as spiritual foundation in a landscape of inner personal comfort zone and safety, Ketu, lord of rajasic (active, excitable, energised) nakshatras in the stages of the journey, bursts those bunds and flattens the landscape. Ketu takes us further into the war of the outer senses versus the inner instruments of action, the antarkaranas, the mind, the intellect, the consciousness, and pushes back the boundaries within toward the all-pervading consciousness.
This is clearly indicated by the nakshatras Ketu has lordship of; each of these nakshatras is a marker of growth from conscious (man is homo sapiens sapiens - man is conscious and has the capacity for self-awareness, the foundation of wisdom; hence the Greek sapiens) to conscience ( the use of buddhi, intellect) and consciousness, awareness beyond the five senses (chitta). Each nakshatra marks stages in the journey, from mind to intellect to consciousness. This is process of acquiring knowledge, entering into knowledge, and practice of knowledge taking us to a deeper knowing and awareness. This, is the task of Ketu in taking us to the goal of life, moksha, freedom from the cycle of birth and rebirth.