What are Rahu and Ketu? Why are they not considered planets in Jyotish Shastra?

In Vedic astrology, unlike other planets, Rahu and Ketu are not physical planets but are shadow planets (Chhaya Grahas). While the Earth is orbiting around the Sun, the two intersection points where the Moon's orbit and the Sun's path intersect are referred to as Rahu and Ketu.

According to mythological stories, after the nectar of immortality (Amrit) was obtained from the churning of the ocean (Samudra Manthan), a demon named Swarbhanu disguised himself as a god and consumed the nectar, at which time Lord Vishnu severed his head from his body using the Sudarshan Chakra. Due to consuming the nectar, Swarbhanu achieved immortality, but because of this, the head portion of Swarbhanu is called Rahu, while the headless torso is called Ketu; that is why Rahu and Ketu are always situated in opposite houses from each other in a birth chart.

Even though Rahu and Ketu are not physical planets, in the context of Vedic astrology, they are considered extremely important, highly effective, and impactful planets. In astrology, Rahu is the significator of deception-fraud, cunning diplomacy, ambition, foreign languages, and material success, whereas Ketu is the significator planet of spirituality, internal development, and detachment. In other words, human life is a quest for material and spiritual things, and Rahu and Ketu are the significator planets for both the material and spiritual dimensions in the universe.