Rahu and Ketu are two
sensitive points of
intersection of the Moon orbit with the ecliptic, These
points are directly opposite each other and change sign in about 18 months and
during span of 18 years they complete one Paraya or one cycle of revolution of
the zodiac. Their movement is constantly retrograde, meaning, against the normal direction of movement of planets.
Even though they are not
physical planets, yet they are perhaps the most influential forces in the
chart. It is along the Rahu / Ketu axis that the main forces of karmic desire
are seen.
In mythology, The Nodes are actually demons,
because they are the eclipse points and they even have the power to devour the
luminaries: The Sun and The Moon.