Rahu and Ketu are two nodes of Moon and they are regarded as full-fledged planets in Vedic Astrology. They are considered as most dreaded planets due to their heavy karmic effects.

Rahu is the Dragon's head and Ketu as Dragon's tail. Both of them form a malefic yoga, known as KalSarp Yoga. There are multiple reasons and views on this yoga or dosha.

Most of the the Kalasarpa dosha effects are negative, while few can be positive too.

Rahu or Ketu gives sudden positive changes which are huge and can happen overnight or within a span of few days. But these effects are temporary and will vanish soon.

Rahu is more independent than Ketu in giving karmic effects.

In Astrology, this Dosha or Yoga is supposed to have direct impact on the following events :

It causes deterioration of health and reduces longevity.

It causes imprisonment or serious accident.

It causes separation, divorce and marital discord.

It causes poverty and destruction of wealth.

It causes destruction of business and loss of job.

It causes destruction of kingdoms and rulers.

It causes downfall of most powerful persons in politics.

Formation of Kalsarp Dosha or Yoga:

All the planets should be within the orbit of 'Rahu and Ketu'.

Rahu should be at the upper end and ketu at the lower end.

There is no planet outside the arch.

That there is no planet conjuncting with Rahu or Ketu.

That all the seven planets should face Rahu,which is always retrograde.

Impact of KalaSarpa Dosh or Yoga:

Rahu in first house and Ketu in 7th house: Downfall, loss of position and reputation, mishappening, marital discord, loss of wife and children.

Rahu in second house and Ketu in 8th house: Reduction in wealth and health causes poverty, worries defects in body and lot of travelling.

Rahu in 3rd house and Ketu in 9th house: Involved in criminal activities, unpopular, waste energy and wealth, selfish, accident prone and paralysis is possible.

Rahu in 4th house and Ketu in 10th house: Loss of property, disappoint-ment, loss of job and business, unhappiness, sarpdosha unhappy and unsettled life.

Rahu in 5th and Ketu in 11th house: Heavy losses in litigation, failure in love affair, loss of children and betrayal by friends.

Rahu in 6th house and Ketu in 12th house: Imprisonment, secret enemies, bad health and serious sickness and set backs in married life.

Note: The impact is more severe if Rahu has support of Sun and Saturn through conjunction(s) or aspect(s)

Duration of Kala Sarpa Dosha or Yoga :

Rahu in 1st house: upto 27 years of age.

Rahu in 2nd house: upto 33 years of age.

Rahu in 3rd house: upto 36 years of age.

Rahu in 4th house: upto 42 years of age.

Rahu in 5th house: upto 48 years of age.

Rahu in 6th house: upto 54 years of age.

Important effects of Kalasarpa Dosha based on influence of other planets :

It causes malefic impact on houses occupied by Rahu and Ketu.

It spoils the benefic planets joining with Rahu and Ketu.

It causes severe hardship when related with Sun and Saturn or the lords of the houses occupied by Sun, Saturn,Rahu and Ketu.

Its impact will be clearly noticed during periods and interperiods of Rahu and Ketu.

Its impact is more severe when Rahu/Ketu are in 1,5 or 9th position from themselves or Sun, Mars and Saturn.

Sometimes it pushes a man to great heights, but that is temporary effect.

Sometimes it gives benefic results, when Rahu/Ketu are aspected by benefic planets, specially Jupiter or Venus.

In case Uranus, Neptune or Pluto are outside the arch of Rahu and Ketu, effects of Kalasarpa Dosha or Yoga are negligible.

Ketu's aspect is less malefic than Rahu.

Powerful Raja Yogas in the chart are more effective than KalSarp Yoga.

Yoga causes great harm to the family, society and nation.

joining ninth Mars in any chart create criminals or suicide or serious accident or murder.

Rahu and Saturn joining in any house destroys the house opposite to them.

Rahu in transit creating relations with Jupiter or Venus gives benefic results.

Ketu moving over any planet is evil for the significations of the concerned house.

If Ascendant is outside the arch of Kal-Sarp Yoga, the malefic impact of Kalasarpa Dosha is reduced.

The dispositors of Rahu and Ketu also play important role in determining the benefic or malefic impact.

Rahu in 3rd or 6th house in Aries, Taurus or Cancer sign does not give malefic results. It is benefic and gives benefic results. Rahu in 10th house or aspecting 10th house and its lord along with Sun and Saturn destroy the native's career. In case of 7th house, separation and divorce is possible.

Rahu and Mars in 3rd house causes accident and damages to life.

Rahu + Mars + Saturn in ascendant : Dangerous personality.