The Sun is a star and Moon is a satellite, but in astrology they are considered as planets because they affect us. Rahu and Ketu have no physical body, but they are considered as planets.
As Rahu and Ketu hold the influence, these are considered Graha. The same is true for Sun and Moon.
Rahu and Ketu are like a black hole in the space, they observe everything that is close to them, they give result as per their placement of houses, signs, planet conjunctions, planetary aspects, Nakshatra (constellation), etc. Due to this nature, we can say that Rahu and Ketu are the most powerful planets in Kaliyuga. They take energy from the other sources and become more powerful like a black hole.
Every planet, satellite, stars is rotating and revolving like Moon to Earth, Earth to Sun and so on. The revolving path of Sun, is called Ecliptic. Rahu is basically the point of intersection between the revolving Moon and South to North course. It is also known as ‘ascending node’ or ‘the North’. The point where the Moon crosses the ecliptic while travelling from North to South is known as Ketu, the South or ‘descending node’. So, these two intersection points are Rahu and Ketu. These two lunar nodes have clubs of magnetic and gravitational forces. That’s why they rule electricity, magnetic areas, hidden things, hidden disease in human life.
Rahu and Ketu comes into the picture during the churning of the ocean in the Hindu mythology. There is a tale of terrible battle between Gods and demons, both started fighting with each other for Amrit (immortality potion). Gods prayed Lord Vishnu to solve this problem. Lord Vishnu changed his appearance as a beautiful woman “Mohini”. The demons were impressed by this beautiful lady “Mohini”. Mohini (Vishnu) asked deities as well as demons to stand in a queue. One of the demons named “Swarbhanu” understood the secret of Vishnu and he changed his look as a deity and stood in the line of the deities. Swarbhanu also took the Amrit with other deities. The two deities Sun and Moon recognized him that he was a demon. Sun and Moon informed Lord Vishnu. Lord Vishnu killed Swarbhanu by Sudarshan Chakra in two parts. But till that time Swarbhanu had taken Amrita, so he became immortal. The head of Swarbhanu is called Rahu and rest of the body is called Ketu. Even today, the demon “Swarbhanu” (Rahu and Ketu) takes his revenge from Sun and Moon by overlapping them as a shadow. We know this event as eclipse.
In Vedic Astrology, Rahu is powerful in Aquarius and Ketu in Scorpio. Rahu is exalted in Taurus and debilitated in Scorpio. Ketu is exalted in Scorpio and debilitated in Taurus – such placement of Rahu and Ketu is very powerful.
Rahu and Ketu amplify the good energies of benefic planets.
Rahu and Ketu bring good results when placed in third, sixth and eleventh houses.
Rahu and Ketu are such Karmic forces that it can restrict a person from enjoying any good effects of the planets. Suppose, Ketu is placed in Virgo and Rahu is placed in Capricorn, and all other planets are placed in the houses between Rahu and Ketu, it creates Kal Sarpa Yoga. This is when a person’s fate is said to be locked in the bad energies of past Karma.
An afflicted Rahu can make you indulge in excesses of life that leads to self- destruction and a bad Ketu can bring obstacles that will hamper your progress towards your goal.