What is Guru Chandala Yoga in vedic astrology?

The conjunction of Jupiter with either Saturn, Rahu, or Gulika gives rise to Guru-Chandala Yoga.

Jupiter is a satvika planet representing purity. Saturn, Rahu, and Gulika are impure planets or chandalas. Literally, a chandala is one who deals with dead human corpses, and therefore a tainted, untouchable person who does base deeds, according to Hindu belief.

So, the combining of the holy planet Jupiter with one of the aforementioned impure planets is said to degrade the effects of Jupiter, making the native cunning, unconscientious, immoral, and wicked.

In practice, it has been observed that this Guru-Chandala yoga is not necessarily bad in many cases. In fact, great Saints have had this yoga.

The good or bad effects this yoga might produce are largely based on the position of the planets involved, their dispositor's strength, and associations or aspects of other planets.