Rahuराहु

Rahu is the eighth of the Navagraha, and he is not a planet. He is the ascending lunar node — one of the two points where the moon's orbit crosses the ecliptic, and therefore one of the two positions at which eclipses can occur.

This is the striking thing about him: the tradition assigned deity status to a mathematical point. Rahu and Ketu are chhaya grahas, shadow planets, with no physical body, and their inclusion in the nine is a direct consequence of Indian astronomers understanding what causes eclipses.

Mythologically he is the severed head of an asura who stole a mouthful of amrita at the churning of the ocean and was decapitated by Vishnu after the nectar had already reached his throat — leaving the head immortal. He pursues the sun and the moon, who exposed him, and swallows them; because he has no body, they pass through and reappear. That is the eclipse.

He is associated in the astrological tradition with obsession, ambition, foreignness, illusion and sudden reversal, and is regarded there as difficult. His worship, correspondingly, is more about propitiation than devotion.

The Rahu narrative is old, appearing in the Mahabharata and developed in the Vishnu and Bhagavata Puranas: the churning of the ocean, the theft of a mouthful of nectar, the disguise among the gods, the exposure by Surya and Chandra, and the beheading by Vishnu's discus.

What makes Rahu genuinely interesting is the relationship between that story and the astronomy. Indian astronomers understood the geometry of eclipses well: the Surya Siddhanta and the work of Aryabhata in the 5th century CE describe eclipses as caused by shadows — Aryabhata explicitly stating that the lunar eclipse is the earth's shadow on the moon and the solar eclipse the moon covering the sun.

So the tradition held both accounts simultaneously, and the reconciliation is elegant: the lunar nodes — the two points where eclipses are geometrically possible — were identified as Rahu and Ketu. The demon who swallows the sun and the point in space where an eclipse can occur became the same thing. The myth was not discarded when the mechanism was understood; it was mapped onto it.

The splitting of one asura into two grahas — head and body, ascending and descending node — completes the mapping, since eclipses require both nodes.

As a graha Rahu enters the Navagraha scheme in the early centuries CE, and the Brihat Parashara Hora Shastra gives him his character: shadowy, amplifying, associated with what is foreign, hidden, or obsessively pursued.

Rahu is shown as a head without a body — the most distinctive image among the Navagraha.

Where he is given a fuller form he appears with a dark or smoky complexion, seated in a chariot drawn by eight black horses, holding a sword, a shield and a trident, with the lower body absent or wrapped in shadow.

He is frequently depicted with a serpent's tail rather than legs, or emerging from coils, and the serpent association runs through both nodes — Rahu and Ketu together are sometimes called the head and tail of a great snake.

As a Navagraha he faces south in the nine-planet shrine.

His gem is the hessonite garnet (gomedh), his grain urad (black gram), his cloth black or dark blue, his metal lead, and his direction southwest. Everything associated with him is dark, and his shrine is visually the most sombre in the Navagraha group.

Rahu as a Navagraha — the eighth of the nine, his principal presence.

Svarbhanu — his older name in the Rigveda, where a figure of that name is said to have struck the sun with darkness. This is the earliest layer of the eclipse material.

The ascending node — his astronomical identity, the point where the moon crosses the ecliptic going north.

Rahu Kalam — not a form but a daily period named for him, observed particularly in South India.

Naga Rahu — his serpent-associated form, worshipped at some shrines alongside Ketu as a pair of serpents.

The churning of the ocean. When the amrita is finally recovered, Vishnu takes the form of Mohini to distribute it, giving it to the gods and withholding it from the asuras. The asura Svarbhanu disguises himself and sits among the gods. Surya and Chandra recognise him and alert Vishnu, who strikes off his head with the Sudarshana chakra — but the nectar has already passed his throat. The head is immortal, and so is the body. They become Rahu and Ketu.

The eclipse. Rahu pursues the sun and moon in revenge for their exposure of him, and periodically catches and swallows them. Having no body, they pass through and emerge. The story explains both why eclipses happen and why they end.

The Rigvedic layer. RV 5.40 describes the asura Svarbhanu striking the sun with darkness, and the sage Atri restoring the light — the oldest form of the eclipse narrative, before the churning story attached to it.

Rahu's serpent form. In several regional traditions the two nodes are the head and tail of a serpent that encircles the ecliptic, and serpent worship and node worship overlap considerably in South India.

Rahu's worship is propitiatory rather than devotional, and it is concentrated in South India.

Rahu Kalam is an inauspicious period of roughly ninety minutes occurring at a different time each weekday, during which new undertakings are traditionally avoided. Observance of it is very widespread in Tamil Nadu, Karnataka and Andhra Pradesh, and considerably less so in the north.

His offerings are dark: black or blue cloth, urad dal (black gram), black sesame, coconut, and hessonite where a gem is used. Saturday and Sunday evening are associated with him in different regional practices.

Rahu-Ketu worship at Kalahasti — the Rahu Ketu Sarpa Dosha rite performed at Srikalahasti in Andhra Pradesh — draws very large numbers, and the temple runs the ritual continuously through the day.

Serpent worship and node worship overlap: Naga Panchami and the offering of milk to serpent images are frequently connected with the nodes in South Indian practice.

In the astrological tradition his eighteen-year period (mahadasha) is watched closely, and he is associated with sudden change, obsession and matters that are hidden or foreign. These are beliefs held within Jyotisha, described here rather than endorsed, and the volume of commercial ritual service sold on the strength of anxiety about them is considerable.

The Navagraha Stotra, the Rahu Kavacham and ॐ रां राहवे नमः are the standard recitations.

Srikalahasti, Andhra Pradesh — the principal site for Rahu-Ketu rites, and also one of the Pancha Bhoota Sthalams as the air element temple.

Thirunageswaram, Tamil Nadu — his shrine among the nine Navagraha temples around Kumbakonam; known for the milk offering that is said to change colour, a phenomenon that has been examined and attributed to the vessel and lighting.

Rahu shrines within Navagraha groups across South Indian temples, where he is installed facing south.

Naga temples across South India where the nodes are worshipped in serpent form, including Kukke Subramanya in Karnataka.

He has essentially no independent temples in North India, where node worship is far less developed.

Rahu is the tradition's most elegant instance of myth and mechanism coexisting. Indian astronomers knew by the 5th century that eclipses are shadows — Aryabhata says so plainly. The tradition did not therefore abandon the story of the swallowing demon. It identified the demon with the lunar nodes, the two points at which the geometry permits an eclipse, and both accounts became true at once: the eclipse happens where Rahu is, and Rahu is where the orbits cross.

That a point in space was given a body, a biography and a shrine is worth sitting with. Rahu has no mass and no light; he is a coordinate. The tradition made him the eighth of nine grahas anyway, and gave him the most memorable image of the set.

His immortality is the cruel part of the story. He drank enough nectar to become deathless and was severed a moment too late, so he cannot die and cannot be whole. What he pursues — the sun and moon — he catches endlessly and can never keep, because he has no body to hold anything. As a picture of insatiable pursuit it is exact, and it is why the astrological tradition gave him obsession to govern.

And the fear around him deserves the same note that Shani's does. Rahu Kalam, sarpa dosha and the eighteen-year period sustain a large market in ritual services. The tradition's own texts treat the nodes as significators to be understood, not calamities to be bought off, and that is the better guide.