What Are Lunar Nodes? Astronomy and Rahu–Ketu Symbolism
The two intersections of the lunar orbital plane and ecliptic, eclipse seasons, and their separate role in Jyotish.
Where the Moon's orbit crosses the ecliptic
The Moon's orbital plane is inclined by about five degrees to the ecliptic, the plane of Earth's orbit around the Sun. The two crossing points are the lunar nodes. At the ascending node the Moon crosses from south to north of the ecliptic; at the descending node it crosses in the opposite direction. A node is a geometric point, not a physical planet.
The two points lie opposite one another on the ecliptic by definition. Their positions shift over time as the lunar orbital plane precesses. Some ephemerides provide a mean node and others a true or oscillating node; different conventions need not yield identical degrees at every instant.
Why nodes are related to eclipse seasons
New Moon alone does not guarantee a solar eclipse, nor does Full Moon guarantee a lunar eclipse. The Sun and Moon must also be close to the lunar node line for a sufficiently close three-body alignment. This explains why eclipses cluster into seasons rather than occur at every new or full Moon.
For example, a New Moon far from either node passes north or south of the Sun in the sky and produces no solar eclipse for Earth. A New Moon close enough to the nodal line can cast the Moon's shadow onto Earth. The detailed outcome still depends on three-dimensional geometry and apparent angular sizes.
Rahu and Ketu are symbolic names for nodes
In Jyotish the ascending or north node is commonly called Rahu and the descending or south node Ketu, with schools choosing mean or true node conventions. The underlying geometric points are real astronomical constructs; claims about destiny, desire or release associated with them are interpretations rooted in the tradition.
When comparing chart software, check the node model, zodiac reference and ayanamsha before declaring one system incorrect. The eclipse article explains where the resulting alignments are visible on Earth; the Jyotish chart can then be used to inspect the traditional symbolic placements separately.
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Sources and methodology
References for checking the astronomical and calendrical facts in this guide. Traditional interpretations are not astronomical measurements.