Astronomically Rahu and Ketu are not planets but the North and South nodes of the Moon. Nevertheless according to Vedic Astrology they are considered shadow planets or Nodes of the Moon.
They don’t have Houses in the Zodiac but they acquire power from the House where they occupy. For instance Rahu and Ketu are moving into Libra and Aries respectively. Rahu will get the power of Venus who is the Lord for Libra. Similarly Ketu will get the power of Mars who is the Lord of Aries.
Rahu is a head without a body, the bodyless head.
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.