Lunar Nodes (Rahu and Ketu)
The lunar nodes are the two points where the Moon’s orbital path intersects the ecliptic (the Sun’s apparent path). The ascending (north) node (Rahu in Vedic astrology) is where the Moon crosses into the northern ecliptic hemisphere; the descending (south) node (Ketu in Vedic astrology) is the opposite crossing. These nodes are essential to eclipse timing: eclipses occur only when a new or full Moon is close to a node.
Vedic Perspective: Rahu & Ketu
In Vedic astronomy and astrology (Jyotish), the lunar nodes are known as Rahu (the Ascending/North Node) and Ketu (the Descending/South Node). Instead of physical bodies, they are classified as Chaya Grahas (shadow planets) because they have the power to obscure the luminaries during an eclipse.
The Mythology of the Shadow Planets
According to ancient Indian mythology, Rahu and Ketu were originally a single immortal demon (Svarbhanu). During the churning of the cosmic ocean, the demon snuck a sip of the nectar of immortality. The Sun and Moon spotted the deception and alerted Lord Vishnu, who immediately sliced the demon in half with his Sudarshana Chakra.
- Rahu (The Head): Having swallowed the nectar, the head remained immortal. It represents unquenchable worldly desires, obsession, and future ambitions.
- Ketu (The Tail): The headless body represents detachment, past-life karma, and ultimate spiritual liberation (moksha).
Because the Sun and Moon exposed them, Rahu and Ketu continuously chase the luminaries across the ecliptic, "swallowing" them during eclipses as eternal revenge.
Astronomy & timing
- Why nodes matter: the Moon’s orbit is tilted ~5° to the ecliptic; alignments at (or near) nodes enable lunar/solar eclipses.
- Nodal precession: the line of nodes precesses (retrograde) around the ecliptic in about 18.6 years, shifting where eclipse seasons occur.
True Node vs. Mean Node (ephemerides)
- Mean Node: an averaged motion (always retrograde).
- True Node: includes short‑term oscillations (can briefly turn direct).
- Separation: typically within about a degree (often cited within ~1–1.5°).
Most ephemerides let you choose which nodes to display. For now AstroClock only uses True Nodes.