and KetuThe Invisible Planets
Why do Hindus believe that the mythological demons
Rahu and Ketu cause solar eclipses?
In Hindu mythology there is a wonderful story that describes
how the gods and the demons once formed an alliance to produce
a nectar that could give them immortality. This is the story
of the churning of the milk-ocean and the descent of Lord Visnu
as the Kurma avatara, the divine tortoise.
When the nectar that was churned from this ocean was being served
to the gods, a demon, disguised as a god, sat between the Sun
and the Moon in an attempt to procure the nectar. When he was
detected by the Sun and the Moon, Lord Visnu immediately
severed his head from his body. Unfortunately, it was not fast
enough, for the demon had already tasted a small quantity of
the nectar and had become immortal. Ever since, this demon is
said to wreak vengeance on the Sun and Moon whenever they come
near. The head of this great demon is known as Rahu and
his tail is known as Ketu.
In Hindu astrology Rahu and Ketu are known as two invisible
planets. They are enemies of the Sun and the Moon, who at certain
times of the year (during conjunction or opposition) swallow
the Sun or the Moon causing either a solar or a lunar eclipse.
In Sanskrit this is known as grahanam or seizing.
What perhaps sounds like a childish story is a powerful metaphor for what actually
happens when an eclipse takes place. Rahu and Ketu are the astronomical
points in the sky respectively called the north and south lunar nodes.
To the observer on earth, the paths of the sun and the moon appear
to be two great circles projected on the celestial sphere (see the
diagram). The suns
path, the solar ecliptic, makes a complete revolution in one year. At the same
time, the moons circular path is completed in about one month. Every
month the moon will overtake the sun which moves more slowly. This is called
new moon or in Sanskrit, amavasya. Usually the moons
path passes above or below the suns path and no eclipse occurs. But,
periodically the moon overtakes the sun at the place where their paths intersect.
This causes the sun or the moon to be hidden from the earths view and
is thus called a solar or lunar eclipse. These places of intersection are the
north and south lunar nodes, or as they are referred to in Hindu mythology,
Rahu and Ketu. Therefore, in the symbolic language of mythology, Rahu
and Ketu are said to swallow up the Sun and the Moon. The ancient
Hindu observers of the sky were aware of the cause of the solar and lunar eclipses
and so described the process in the language of metaphor.