Lunar nodes are, from astronomical perspective, two imaginary mathematical points in space on Moon’s orbit, in which it crosses the ecliptic – the Sun’s imaginary path around the Earth. They are the points in which the paths of the Sun and Moon meet, observing from the Earth. The North lunar node represents a point in which the Moon ascends over ecliptic, while the South lunar node is a point in which the Moon descends beneath ecliptic. They are set in opposition. They only move retrograde with an average speed of around three minutes a day, and they pass the full zodiac circle in around eighteen and a half years. 
 
Mitology
A long time ago, there was a war between gods and demons, the good and evil. 
Apart from them, the world contained the souls of the future big Rishis in the body of Nagas, snake-like creatures that moved upright. Their leader was Vasuki, the king of snakes. While observing constant fights between demons and gods, Vasuki came to an idea and went to the supreme god Vishnu asking for help and blessing. He asked what they should do in order for demons and gods to get peace and stop the war. He got the answer. Stir the ocean, in order to get a cup with nectar Amrit. It would make them immortal and powerful, everyone would enjoy its effects and the fights would stop. The condition is that the nectar would be available to everyone. 
Vasuki, after Vishnu’s blessing, suggested that gods and demons reach peace together and make balance, because none of them has enough strength alone. The king of snakes Vasuki suggested that demons and gods tie him to a mountain Mandrachal to serve them as a rope to go down into the ocean and, by moving the mountain, stir the water. 
The gods were holding the body, and the demons the head of the god of Snakes, and the process was ready to begin. Unexpectedly, by stirring the ocean, something came out of it that nobody expected. First, it was a cup of poison Vish, which provoked chaos in all three worlds. The god Shiva quickly took the cup, drank everything in order to save the world, not noticing that one drop ran down his neck that stayed blue forever. 
Dhanvantari (Avatar of Vishnu, doctor of Gods) finally caught the cup with nectar Amrit. Seeing that, the gods and demons all jumped to take the cup. At that moment the god Vishnu transformed into the beautiful dancing lady Mohini and offered the cup to gods and demons in the same time, putting them into two separate rooms. Of course, he gave the cup only to gods, secretly. One night, Vasuki sneaked to gods, stole Amrit and drank a sip. Seeing that, Vishnu threw his disc and cut Vasuki into two. Since he already took a sip of immortality nectar, Vasuki couldn’t die and his separated parts continued living. The supreme god Vishnu sent each part of the God of Snakes body to two opposite parts of the Earth. That is how Rahu snake (demon) head and Ketu snake tail (demon body) were made. 

Astrology
North and South lunar nodes, Ketu and Rahu, most simply said, represent a karmic mission, a task in someone’s life. Nodes, further on, indicate relations which we will build with surrounding, weak spots in someone’s life and so on. 
They are both primarily malefic. Rahu will always act secretly, while Ketu will have an open action. 
The 6th house belongs to Rahu, and the 12th to Ketu. Exaltation of Rahu is in the 3rd or the 6th astrological house, while in the 8th, 9th, 11th and 12th house it gives bad results. 
Rahu rules the upper part of the body, Ketu rules the lower part. Rahu rules the chin, Ketu rules the big toe. North lunar node or Rahu is, in astrological literature, brought into connection with harmony, essential striving, indicates incarnation lessons that we should receive now and the path to follow. Since it represents a Head (of a dragon, snake) without body, Rahu indicates an area that all our mind and consciousness will be focused on. Rahu rules material things and is not so interested in the essence of relation.
Rahu can show bad reputation, malicious deeds, difficulties and bad periods in life. “To bang your head” because of something would be the right word. “The thoughts of the entire life” concentrated to a certain area. Rahu is looking forward to Mercury and it would be ideal to have them in the 4th house. Also, it would be perfect for Rahu to be in astrological houses before Saturn (e.g. Rahu in the 3rd, Saturn in the 8th). As opposed to it, Ketu will give you great fun, happy circumstances, but also beheading especially in aspect with Jupiter. 
 
Let us take, for instance, Grace Kelly 
(November 19th, 1929, 5:31 AM, Philadelphia, PA, USA)

 The first thing that we see is Rahu in the 7th house next to Chiron in Taurus. A head turned to partnership, marriage. Solving of financial debts of the partner, difficulties in marriage and a deep hurt through marriage. It is interesting that Aristotle Onassis bought a casino in Monte Carlo in 1953 and the economy of Monaco started to decline. Gardner Cowles, the publisher of Look magazine, brought up that a marriage of prince Rainier with a Hollywood star could attract rich tourists to Monaco (referring to Merlin Monro). 
Two years later prince Rainier “accidentally” met Grace Kelly at Cannes festival in 1955, and thought that she could be a matching wife and a princess of Monaco. Rainier had to get married because of inheritance (money - Taurus), or if he wouldn’t have an heir to Monaco’s throne, his principality would belong to France. 
Because of bad economic situation in Monaco, Rainier demanded 2 million dollars dowry from Grace’s father. That’s Rahu in the 7th house in Taurus.
It is interesting to analyze Rahu from natal chart in conjunction with partner’s Venus. The first association would be “I cannot get this person out of my head, this is true love and I know it”. These are certainly karmic loves that have to come true now in any possible way. These two persons run one to another, they rush into relationship, they have a feeling that they know each other forever and they usually start a relationship no matter what. Of course, this does not mean that the relationship will last forever. In this case it did, at all costs. 

Ketu or South Lunar node depicts our earlier incarnation experiences, but also the origin and all characteristics of our ancestors that we bear genetically. It clearly depicts the decisions made in previous lives, experiences that we strongly bear, old weaknesses that we “fall” on, longtime acquired talents, knowledge and skills.
Rahu is, literally speaking, obsessed with things and persons from material world. Ketu is trying to free itself from them. Ketu “swallows” everything wherever you find it.
The basic need of Ketu is to return to already “familiar things, people, knowledge” and to clam up. Moreover, Ketu signifies deprivation, insecurity, fears, “beheading”, body with no head, realization that something is not good for us, and again we are unable to escape form the same, pure pleasure and the body of a demon. Ketu looks at the things essentially, but it is always unsatisfied with everything from material world and constantly craves for something bigger, higher, better. Eternally unsatisfied, constantly notices only what is missing. Ketu stands for a son, grandson. It rules the bed, rising of the Sun – dawn; and the day – Sunday. It rules black and white color. 
It is interesting to look at Ketu in comparative positions with someone’s planets. 
For example, in male-female relationship Ketu on Venus will bring rejection, hurt and abandonment. It is absolutely certain that in the same time this is a karmic debt toward a person whose Venus is attacked by Ketu. And Ketu will come to take what’s his. 
For illustration, we will say that this relationship will start with a Venus feeling “I know this is very bad for me, but I cannot escape from him/her”. Magnetically attracted Venus, wrapped with a snake’s body so that it cannot escape Ketu, no matter how consciously it suffers, obsessed by a demon’s body and passionate pleasure of giving, it will certainly be abandoned by Katu. 
Someone’s Saturn on your Ketu, on the other hand, will bring inseparable connection and relationship that will give you important life lessons, hard and a bit bitter experiences, burden and discomfort, useless advice, etc. 
First, find a house where your Ketu is, on which degree and in which sign. After that, look at the aspects with other planets. 

Ketu in houses – basic principles:
Ketu in the first house usually symbolizes taller person. Body is in the forefront. A person sacrifices him/herself and is at service to others that could damage him/her materially. 
Egoism and the need to clam up are inevitable. With Ketu in the first house, the person will constantly be worried and he or she may worry about a child or a spouse. Also, Ketu in the first house will bring important experience on a journey and a life outside the place of birth at least in one moment. This position is (along with other aspects) more beneficial for a father. 
Ketu in the second house indicates pleasure in someone else’s money (most often mother’s, wife’s), and supporting by others, bad income, big expenses, losing of inheritance from father’s side. Discontinuance of work that could last long. Material losses and bad genetic judgments. 
Ketu in this field exhibits bad health because of bad nutrition. “Losing of head” because of depths, money. From the age of sixteen to twenty major life turnovers happen. 
Ketu in the third house indicates problems with fine and gross motor skills. Problems in speech, thinking, movement or too loud and intrusive person. Most often, a person with Ketu in the third house gets a job that will take him/her to distant travels. Strong orientation towards education, spirituality, long stays abroad and easy acquiring of foreign languages. Success in publishing and with law, but also danger in traffic, life danger of younger brother or sister and break up of communication with relatives. Twenty-fourth year of life is important. 
Ketu in the fourth house indicates losses in real-estates, bad genetics, loss of patriotism and loss of contact with parents. Unmarked, unknown grave. This position of Ketu brings life danger for a parent or separation of parents (divorce). Fears. On the other hand, Ketu gives long life to a person who has it in this house. Thirty-sixth year of life is significant. 
Ketu in the fifth house symbolizes losses and damage through love relations, children, sport and fun. This position of Ketu indicates enjoying in body pleasures and loss of pregnancy (whether intentional or accidental). It makes damage to father income and personality, fall in position to a spouse and waiting for children from age 36 to 42.
Ketu in the sixth house indicates long life and happiness related to mother and harmonic life. If aspects are bad it will bring skin problems, problems at work, job loss and health problems. Serious changes and dangers come at the age of 17 and 18. Losing of brothers or sisters. Ketu in the sixth house brings enemies at work, fears.
Ketu in the seventh house indicates the loss of the first husband/wife, losses through the second child and problems in public. 
Suffering is possible until the age of 34 on emotional plan and concerning family relations. Ketu in the seventh house gives money in 24th and 40th year of life. 
Ketu in the eighth house shows the loss of inheritance, stocks on the stock market, bad financial situation of a spouse, loss of the first child’s home. In a female horoscope it shows difficulties in the first pregnancy. The one who is born gives false promises and can be rejected from his/her nearest. Life danger is high on operating table. Bad aspects of Ketu in the 8th house marks shorter life expectancy. 
Ketu in the ninth house suggests danger on the road and during the studies. Discontinuance in education or loss of the second marriage or the third child. Break up of communication with partner’s family or their losses or losses related to them. Urinary problems and back pain. Huge turnovers from the age of 19 to 24. Job loss to a father or a health problem.
Ketu in the ninth house symbolizes losing of honor and position, separation of parents, earlier loss of one of the parents, family worries, business losses from age 37 to 42. Strong patriotism and attachment to a family house. 
Ketu in the tenth house symbolizes losing of plans, friends and hopes. Hardships with retirement and losing of older brothers or sisters. Marriage with a person who could have (or has) a child. Financial gains and a great fortune but not enough children and worries related to them. 
Worries for future and dissatisfaction with what is achieved. Stomach problems. 
Ketu in the twelfth house indicates high position, good finances and helping the older. Dangers over the ocean or in the closed institutions. Fears, mental anxiety, bad dreams and losing of godfathers. Intrigues and disclosing of secrets.