Rahu and Ketu arise from Hindu Mythology and are important in Vedic astrology.
Rahu is the "Dragon's Head" and is associated with the North Node of the moon. Ketu is the "Drogon's Tail" and is associated with the South Node of the moon. Rahu rides a chariot of darkness drawn by eight black horses and is said to be responsible for lunar and solar eclipses.
Rahu was the eldest of 100 brothers, born to Simhika and Viprachitthi. Raahu is an asura (unlike other planets). He was born with a serpent head.
The myth of Rahu and Ketu sheds much light on their function and greater possibility. Shortly after the beginning of time, the Gods and demons were in a terrible war, neither side making any progress. So they decided to join forces and churn the milk ocean to get the pot of amrita (immortal nectar) at the bottom. Once the nectar was extracted then came the job of distributing it. The Gods, not wanting the nectar to fall into the hands of the demons, devised a plan. Lord Vishnu disguised himself as the enchanting and beautiful Mohini to distribute the nectar. The Gods and Demons were seated on two different sides of an aisle as Mohini distributed the nectar to the Gods only. The demons were too enchanted by her beauty to notice she was not giving them the nectar. However one demon, Rahu, noticed what was happening and disguised himself as a God and managed to get a drink of the nectar. As soon as this happened, the Sun and Moon told Lord Vishnu what was happening and Vishnu returned to his form as Vishnu and let fly his sudarshan and chopped Rahu in half, but only after Rahu managed to take a drink of the nectar. Thus he is immortal, but chopped in half. The head is Rahu and the tail is Ketu.
Rahu and ketu hold an eternal grudges against Surya and Chandra takes every opportunity to devour them. This causes an eclipse. which ends when the Sun or Moon emerges from Rahu's severed neck.
Rahu is a head without a body. Everything he comes into contact with he becomes obsessed with, like a person with a voracious appetite. Rahu represents material desire, but because he is not a physical planet he operates on the subconscious level. He distorts our perceptions and colors the world according to his desires. He tends to obliterate the essence of things, focusing on their material substance. He is our deepest subconscious material desire. Rahu obsesses over the things we need to learn so we can eventually be freed of them. There are certain lessons we can only learn in a physical body, in the physical world. Rahu's obsessions indicate those things. All human beings are crazy in some way, Rahu shows the area of life where we are unbalanced and obsessed. Rahu keeps us obsessed until we learn detachment from what he is influencing. As such, he represents attachment. Losing our higher Self to the things of this world is the main reason we suffer in life. Rahu's obsessions bring much suffering as long as we desire experience. Once we desire liberation, Rahu is incredibly spiritual.
Ketu is the other half of the demon, the headless body. Where Rahu obsesses over the things of this world, Ketu seeks to be freed from them. Rahu is material and loses the essence of things in their substance. Ketu perceives the essence of things but is unsatisfied with anything substantive in the world. Whereas Rahu wants to grow and experience new things, Ketu wants to fall back on the familiar and withdraw, creating a fear of stagnation and disgust with the familiar that is often turned inward as self-disgust. Ketu brings doubt and sharp criticism to the areas of life that he sees. Eternally unsatisfied, he only notices what is missing from whatever he is influencing. He presides over the absolute aspect of God. He is strict and exacting and sucks the worldly joy out of all he touches, including the things Rahu is obsessed over through house and sign. It is the push and pull of Rahu's obsession and Ketu's doubt that allows the soul to learn the lessons of the Nodal house and sign placement
Rahu (North Node of Moon): Rahu has the nature of a serpent. It poisons you to the illusions of this world. It is our desires that keep us incarnating here. Under Rahu, things happen. Rahu gives, but with a price. When our most intense desires are granted under Rahu we discover that too much of a good thing ends up causing our most intense suffering. We may, for example, gain fame and fortune, only to realize we have no freedom or place to go without being mauled by fans. Family and friends disown us out of jealousy. The fame and fortune we desired only brought us separation and sorrow. Ultimately the disillusionment leads to the enlightenment of Ketu, who detaches and renounces the world for spiritual enlightenment. The nodes are the most powerful of all the planets, for they cause the eclipses of the luminaries, the Sun and Moon. The nodes block out the light or consciousness. Rahu is the material world and all the desires it creates. It gives material things which will never bring lasting happiness. This is the illusion of Rahu. When these things start to fall away we become obsessed with trying to hold on to them. Rahu deals with fear, obsessive and compulsive behavior. It is about addictions, poisons, alcohol, and drugs. Any planet with Rahu will be magnified greatly in the chart as Rahu will take on the quality of the planet it is next to (in the same sign). This can be good or bad depending on the planet. Rahu with Venus or Jupiter can bring wealth, but Rahu with Saturn can cause suffering to the house they are in.