Rahu and Ketu: two points, one axis

Where the two nodes come from

Earth’s orbit around the Sun defines a reference plane called the ecliptic. Seen from Earth, the ecliptic traces the Sun’s annual path against the sky. The Moon’s orbital plane is tilted by about 5.1° relative to it.

Two intersecting planes meet along a line. Viewed from Earth’s centre, that line points in two opposite directions. These are the lunar nodes. They are positions defined by the orbit, rather than bodies travelling along it.

Rahu (राहु) is the ascending node, also called the north node: the Moon crosses the ecliptic from its southern side to its northern side. Ketu (केतु) is the descending node, or south node, where the crossing goes the other way.

Both nodes lie on the ecliptic. “North” and “south” describe the Moon’s direction of crossing. They do not put Rahu over Earth’s North Pole or Ketu over its South Pole. Rotating the diagram changes the view, but the names stay attached to the same crossings.

Why Rahu and Ketu are 180° apart

The line through the two nodes is the nodal axis. Its ends point to opposite parts of the sky, so the nodes are always half a circle apart in longitude.

Finding one node therefore determines the other. Add 180° to Rahu’s longitude; if the result reaches 360°, subtract 360° to return to the start of the circle.

For example, Rahu at 12° Aries corresponds to a longitude of 12°. Ketu is at 192°, which is 12° Libra. If Rahu is at 350°, Ketu is at 170°. These are illustrative positions, independent of a particular date.

The relationship applies to their original zodiac longitudes. A divisional chart remaps those longitudes and need not show the nodes in opposite signs.

How their positions are calculated

A node position answers a geometric question: where does the Moon’s orbital plane meet the ecliptic at a chosen time?

1. Choose the moment and the node convention. A calculation can describe either the smoothed orbit or the orbital plane at that instant.
2. Locate the ascending direction. For the instantaneous plane, the Moon’s position and direction of motion relative to Earth establish the plane. Its intersection with the ecliptic identifies the nodal axis; the south-to-north crossing identifies Rahu.
3. Measure the longitude. Measure around the ecliptic from the chosen zodiac origin to Rahu.
4. Place Ketu opposite. The same 180° relationship supplies the descending node.

Mean node and true node

The mean node follows a smoothed model of the Moon’s orbit, leaving out short-period variations. Its steady backward progression is useful for describing the long cycle.

The true node uses the instantaneous orbital plane. “True” is the conventional name for this calculation; the orbit continues to change, so it is not a fixed ellipse predicting every future crossing. The true node varies around the mean position and can briefly move forward.

Both conventions keep Rahu and Ketu opposite. Near a sign or nakshatra boundary, their differences can change the displayed placement. Comparing two charts therefore requires checking the node convention as well as the time.

The zodiac supplies the starting point

A tropical zodiac measures from the March equinox. A sidereal zodiac uses a reference tied to the stars, with an ayanamsa specifying the offset from the tropical origin. Changing that origin changes the longitude labels and sometimes the named signs. It does not change the underlying pair of crossings.

The zodiac ring above uses twelve equal 30° signs. They are coordinate divisions, not outlines of the unequal astronomical constellations. Read more about sidereal and tropical zodiacs.

Why the nodes matter for eclipses

At new Moon, the Moon is in the Sun’s direction. At full Moon, it is in the opposite direction. The orbital tilt usually carries it north or south of the alignment needed for an eclipse.

A solar eclipse occurs when the new Moon passes in front of the Sun as seen from part of Earth. A lunar eclipse occurs when the full Moon passes through Earth’s shadow. Either requires the Moon to be sufficiently near a node; it need not be exactly on the crossing.

Either node can be involved in either kind of eclipse. Rahu does not belong exclusively to solar eclipses, nor Ketu to lunar eclipses. The nodes mark the geometry; the shadows are cast by the Moon and Earth.

The alignment view above shows the central geometry. Actual eclipse type, duration and visibility also depend on distances, apparent sizes and the observer’s location.

The axis slowly turns

The Sun’s gravitational influence changes the orientation of the Moon’s orbit. The nodal axis gradually turns backward around the ecliptic, completing a circuit in about 18.6 years. This is a different motion from the Moon’s journey around Earth each month.

The final scene holds the Moon out of view to make that slower change visible. The orbit’s tilt remains, while the directions of its crossings turn together. The animation shows the overall backward drift; the true node also makes brief forward excursions.

Are Rahu and Ketu always retrograde?

Retrograde means moving backward through zodiac longitude, for example from 12° Aries toward 11° Aries. Direct means moving forward, toward 13° Aries. For the nodes, this describes the shifting crossing points. It does not mean the Moon reverses its orbit.

Mean nodes remain retrograde. True nodes can briefly turn direct. The Sun’s pull changes the Moon’s orbital plane, producing short variations around the mean motion. A true node turns direct when its longitude temporarily increases; at the turning instant its longitude speed passes through zero. The description “Rahu and Ketu are always retrograde” therefore fits the mean-node convention.

An hourly sample from 1 January 2000 through 31 December 2025 gives these rounded proportions:

Node model	Retrograde	Direct
Mean	100%	0%
True	74%	26%

These percentages describe the sampled instants in that period, not a fixed annual split. Both nodes move together, staying 180° apart even during a direct interval. Rahu remains the ascending crossing and Ketu the descending crossing; those names describe the Moon’s crossing direction, not the nodes’ drift. The retrograde guide explains the chart’s motion marks.

What Rahu and Ketu mean in tradition

In Jyotish, Rahu and Ketu are counted among the nine grahas and are often called shadow grahas. Their astronomical identity remains the two lunar nodes.

The eclipse story gives Rahu a pursuing, consuming role. In one traditional telling, Rahu drinks the nectar of immortality while disguised among the devas. The Sun and Moon reveal him, his head is severed, and the immortal head later pursues them. The story gives eclipses a mythological form.

One astrological interpretation associates Rahu with desire, ambition and unfamiliar experience, and Ketu with detachment, separation and inward inquiry. These are symbolic readings attached to the two ends of the axis. They are not consequences derived from the angle of the Moon’s orbit.

For example, the same axis can be read through the wish to gain recognition and the experience of no longer valuing it. Reversing Rahu and Ketu preserves the geometric axis but changes which end carries each symbolic role. A particular chart reading also considers the occupied houses, signs and their rulers.

The Rahu guide and Ketu guide cover those interpretive contexts. Rahu Kaal is a separate weekday-based division of daylight; it is not the time when the Moon crosses Rahu.

See the node positions in a birth chart on the Kundli page.