What is "Kala Sarpa Yoga"?

This is a very famous planetary combination, at least in India - where there seems to be quite a dreadful hype over it. However this yoga is fairly common, and therefore cannot (by sheer statistical considerations) be all that great or terrible in and of itself.

To put it franly, Kaala-Sarpa yoga is over-emphasized in popular modern Vedic Astrology.

Kalasarp Yoga occurs when all your planets are between the northern and southern Lunar Nodes (Rahu and Ketu). The two main varieties of the yoga depend on weather Rahu (north node) or Ketu (southern node) is at the "front" of the chain. The yoga is thought to have more severe effects when Ketu is at the front (i.e. the planets are moving towards Ketu).

The idea is that if all the planets are between the body and head of the dragon/serpant's head and tain, Rahu and Ketu - you are under a "curse." Depending on the house placement of Rahu and Ketu you have a different type of curse.

Again, this yoga is over-rated and over emphasized. It may even be a factor causing great fortune in some cases. Paul McCartney of the Beatles, for example, has kalasarpa yoga.