North Node and South Node Explained

The lunar nodes are not planets. They are the two points where the Moon's orbital plane crosses the ecliptic — the plane of the Sun's apparent path — and because two planes meet along a straight line, the two points are always exactly 180° apart. The north node is the crossing where the Moon passes from south of the ecliptic to north of it; the south node is the other end of the same line. Nothing is there: no body, no star, no glow. What makes them worth a page is not the symbolism but the arithmetic. The whole axis slides backwards through the zodiac at about 19.35° a year, completing a circuit in roughly 18.6 years, and eclipses can only happen when a new or full Moon lands close to one of the two crossings. That last sentence is the single most checkable fact in this article, and everything the tradition builds on top of it is inherited symbolism rather than measurement — a distinction this page keeps visible throughout.

Two intersections, not two objects

The Moon's orbit around Earth is tilted about 5.1° to the ecliptic. That small tilt is the reason the nodes exist at all. If the Moon orbited exactly in the ecliptic plane there would be no crossings to name, and — as the eclipse section below explains — there would be an eclipse every fortnight.

Two tilted planes sharing a centre intersect along one straight line. Extend that line out to the band of the zodiac and it pierces it at two opposite degrees. Those are the nodes. Astronomers call them the ascending node, where the Moon crosses northward, and the descending node, where it crosses southward. Astrology calls the same two points the north node and the south node, and older texts call them the head and tail of the dragon — caput and cauda draconis — from a Babylonian and Arabic tradition that imagined the eclipse as a creature swallowing the light.

Because the two points are opposite ends of one line, a single figure describes both. A north node at 14° Pisces is a south node at 14° Virgo, exactly, with no rounding and no exceptions. This is not an approximation that holds most of the time; it is what a line through a centre means. It is also why the nodes are read as one axis rather than as two independent placements — a point the interpretation section returns to.

One consequence shows up in how the Moon's month is measured. The Moon returns to the same star in 27.32 days — the sidereal month — but returns to the same node in 27.21 days, the draconic month. The gap of roughly 0.11 days exists because the node moved to meet it.

Why the nodes always run backwards

The Sun's gravity does not act evenly on a tilted orbit. It pulls hardest on whichever part of the Moon's orbit is nearest, and the net effect over a month is a torque that swivels the whole orbital plane. The plane precesses, the line of nodes swings with it, and the direction of that swing is westward — backwards through the order of the signs.

The rate is steady enough to quote: about 19.35° a year, one full circuit of 360° in roughly 18.6 years, and therefore about 18.6 months in each sign. Divide again and it is about 0.05° a day, which is a fact worth holding on to — it is why the nodes are the one thing in a chart that an unknown birth time cannot spoil.

The word retrograde attaches to this, and it means something different here than it does anywhere else on the site. Mercury and Mars retrograde are apparent effects: the planet keeps orbiting forwards and only appears to reverse because Earth overtakes it, which is covered in what retrograde actually means. Nodal regression is not an illusion of viewing angle. The orbital plane really is precessing, continuously, in that direction, and it has never done anything else. So a headline announcing that the nodes have gone retrograde is describing their permanent condition, not an event. Transits and retrogrades sets the nodal rate beside every other body's if you want the comparison.

Why eclipses only happen near a node

At every new Moon the Sun and Moon share the same ecliptic longitude. At every full Moon they sit opposite. If longitude were the only thing that mattered, every month would bring one solar and one lunar eclipse — about a dozen of each a year.

It does not, because longitude is only one coordinate. The 5.1° tilt means that at a typical new Moon the Moon rides above or below the Sun by up to about five degrees of ecliptic latitude. The Moon's disc is roughly half a degree wide, so that is about ten Moon-widths of empty sky between the two, and no shadow reaches anything. The same miss happens at the full Moon, where the Moon passes above or below Earth's shadow rather than through it.

Near a node, that latitude collapses to nearly zero — a node is by definition where the Moon has no latitude at all. So an eclipse needs two conditions at once, and they run on different clocks: the phase clock of 29.53 days, and the nodal clock the Sun keeps as it passes each crossing.

What has to coincide for an eclipse

1. A syzygy. New Moon for a solar eclipse, full Moon for a lunar one. Nothing else in the lunar month is a candidate.
2. Proximity to a node. At the outer limits, a solar eclipse is possible when the new Moon falls within roughly 18° of a node and a lunar eclipse when the full Moon falls within roughly 12°. Inside those bands something is eclipsed; well outside them nothing is.
3. Then geometry decides the kind. How close to the node, plus the Moon's distance that month, sorts the result into partial, total or annular. Zodiux does not publish an eclipse table and takes no position on any individual eclipse.

The Sun covers about a degree a day, so an 18° band either side of a node takes it about five weeks to cross. That window is an eclipse season, and it is why eclipses arrive in clusters of two or three rather than singly. There are two seasons per eclipse year of 346.62 days — the time the Sun takes to return to the same node — which puts them roughly 173 days apart.

The eclipse year is about 19 days shorter than the 365.25-day solar year, precisely because the nodes are regressing into the Sun's path rather than waiting for it. That difference is why eclipse seasons drift about 19 days earlier each calendar year instead of recurring on the same dates. It also sets the floor and ceiling on how many eclipses a year can hold: never fewer than four, never more than seven.

True node and mean node

The 19.35° a year is an average. Over a single month it is not what the node does. The Sun's tug on the orbital plane varies with the Moon's position and with the Earth's position in its own orbit, so the actual instantaneous crossing wobbles either side of the smooth line — and the two ways of reporting that are why two ephemerides can hand you two different node positions for the same birthday.

The mean node is the smoothed average: uniform regression, the wobble removed. It never moves forwards. The true node is the crossing computed for the instant: the same underlying motion, wobble included. The offset between them rarely exceeds about a degree and a half, and the true node spends short stretches drifting forwards through the zodiac before resuming its retreat.

In practice that gap is small enough to ignore except at one moment. At 19.35° a year the node takes about a month to travel a degree and a half — so mean and true agree on the sign except for births within roughly a month of a nodal ingress. If your birthday falls in that window, look up both before treating either as settled.

Neither is a mistake. They answer different questions: the true node is where the plane crossing actually is at a moment, the mean node is the long-term average that the phrase 18.6-year cycle is defined against. Printed twentieth-century ephemerides usually carried the mean node; most modern software defaults to the true node, and a good deal of it never says which it used.

Zodiux computes neither, which the last section covers. Saying which one a number is remains the useful habit whatever tool you get it from.

What the tradition does with the axis

Here the page changes register, and the change is worth announcing. Everything above is geometry that can be checked. Everything below is inherited symbolism — an interpretive convention with no measurement behind it, offered as description rather than as fact.

The convention reads the south node as the practised end of the axis: the sign and its associated material as something already familiar, the setting a person defaults to without deliberating. The north node is read as the same axis seen from the opposite sign — the less rehearsed end, the material there is simply less habit in. That is the whole structure. The south node in this framing is not a defect and not a warning; it describes what is easy, which is a different thing from what is wrong.

Because the two points are one line, they are always in opposite signs, and there are only six possible axes for the whole population. The nodes are read as one axis with two ends, never as two independent placements — choosing a north node sign fixes the south node in the same breath.

The six nodal axes

• Aries and Libra
• Taurus and Scorpio
• Gemini and Sagittarius
• Cancer and Capricorn
• Leo and Aquarius
• Virgo and Pisces

Some traditions attach past lives to the south node. That is a metaphysical claim rather than an astronomical one, and Zodiux takes no position on it; the nodes as this site describes them are two coordinates and a precession rate. Nothing about anyone's history, obligations or future follows from them.

The register that survives honest handling is the reflective one. Reading an axis as a prompt — what does this describe as familiar, and what does it describe as unrehearsed? — is a question a person answers for themselves, and it is checked against their own experience rather than against the sky. Any version that issues instructions has left what the astronomy can support far behind. Using astrology responsibly sets out where that line sits across the whole site.

The 18.6-year clock: returns and reversals

One cycle length produces every landmark people quote. A nodal return is the transiting axis arriving back where it sat at birth, which takes about 18.6 years — 18 years and roughly 7 months. Halfway through, at about 9.3 years, the axis has swung 180° and sits reversed: the transiting north node occupies the natal south node's degree, and vice versa. Since the two ends are interchangeable geometrically, the reversal is as much a landmark as the return.

The table below is pure arithmetic on 18.6 years. It is not derived from anyone's chart and it is not a schedule of events.

Two caveats travel with that table. The ages are averages of a cycle that is not perfectly uniform, so an individual return computed from a real ephemeris can land a few weeks either side of the printed figure — the true node's wobble is exactly the effect described two sections up. And the transiting axis passing a natal degree is a position, not a promise; nothing is scheduled to occur at any of those ages.

The comparison worth drawing is with the other cycles the site covers. Saturn takes about 29.5 years to come home, putting the Saturn return at roughly 29 or 30 and again near 59. Jupiter's 11.9-year orbit returns at about 12, 24 and 36. The nodal return, at 18 or 19, is the first of the long-cycle returns to arrive — which is most of why it gets talked about.

What Zodiux computes, and what it does not

The free Zodiux chart does not compute the lunar nodes. It reports ten bodies — the Sun, the Moon and the eight planets — plus the Ascendant, each by sign and degree, and that is the complete list. House cusps, the Midheaven, Chiron and asteroids are absent for the same reason: they are outside the scope the tool commits to, and saying so plainly beats leaving a reader to discover it. What we do not claim is the full inventory.

What the site does compute comes from one source. Astronomy Engine, an open-source implementation of the VSOP87 and NOVAS algorithms, is bundled into the page and into the build, so a position quoted on a sign page cannot disagree with the calculator. Every figure is geocentric apparent ecliptic longitude, corrected for light-travel time and aberration, read against the tropical zodiac of twelve equal 30° signs measured from 0° Aries. The live sky and the Mercury retrograde tracker run the same library. There is no eclipse table anywhere on the site; the glossary defines the word and stops.

If you want your own node position, take it from any ephemeris that publishes one — and note two things while you are there. Check whether it says true or mean, and if your birthday is within about a month of a nodal ingress, look up both.