jyotisha and the sky
Who are Rahu and Ketu and what is their mythological and astronomical basis?
The myth behind them
The story comes from the Samudra Manthan, the great churning of the cosmic ocean. Gods and demons churned the sea together to bring up amrita, the nectar of immortality. When it finally appeared, a demon named Svarbhanu slipped in among the gods and drank some. The Sun and Moon spotted him and raised the alarm. Vishnu immediately cut the demon in two with his discus. But the nectar had already touched his throat, so both halves lived on. The head became Rahu. The tail became Ketu. Ever since, the tradition says, Rahu and Ketu chase the Sun and Moon across the sky in revenge, and when they catch them, an eclipse happens.
The astronomical side
Behind the myth is a precise astronomical idea. The Moon travels around the Earth on a slightly tilted path. The Sun appears to move along its own path, called the ecliptic. These two paths cross at two points. The north crossing point is Rahu, and the south crossing point is Ketu. They are always exactly opposite each other in the sky. Traditional texts including the Surya Siddhanta and the Brihat Parashara Hora Shastra describe how to calculate these points carefully. Eclipses happen only when the Sun and Moon line up near one of these crossing points, which is exactly what the myth of the demon catching them describes in story form.
What they mean in jyotisha
Because Rahu and Ketu have no physical body, they are called shadow planets, or chaya grahas. They cast no light of their own. In jyotisha, Hindu astrology, they are still treated as powerful influences. Rahu is linked to worldly desire, ambition, and things that feel foreign or new. Ketu is linked to detachment, past karma, and spiritual turning inward. They always sit opposite each other in a birth chart and move together as a pair. Their eighteen-month stay in each sign is watched closely by practitioners. The period ruled by Rahu or Ketu in a person's planetary cycle is seen as a time of significant change, though how it plays out is read from the full chart, not from Rahu or Ketu alone.
What modern astronomy says
The lunar nodes are real and well-defined points that modern astronomy uses too. They are important for predicting eclipses. An eclipse can only occur when the Sun and Moon are both close to one of these nodes at the same time, which matches the traditional explanation almost exactly. The nodes are not physical objects, so they have no mass or gravity of their own. Whether they influence human life is a matter of belief, and there is no scientific evidence for that part.
Today
Rahu and Ketu remain central to jyotisha practice across India and in Hindu communities worldwide. During a solar or lunar eclipse, many families still connect the event to the old myth. Some observe fasting or prayer at eclipse time. The shadow planets also appear in temple iconography, often shown in the row of the nine grahas. How much weight people give them varies widely, from those who follow their transits carefully to those who know the story but do not consult an astrologer about them at all.