In one paragraph
Rahu and Ketu are the two points in the sky where the Moon's orbit crosses the path of the Sun. Rahu is the northern crossing, Ketu the southern; they are always exactly opposite each other. They have no substance and give no light, which is why they are called shadow planets (chhaya graha). They earn their place among the nine grahas because eclipses can occur only when the Sun and Moon meet near one of them.
The astronomy
The Sun appears to travel round the sky along a circle called the ecliptic. The Moon's orbit is tilted to that circle by about five degrees, so for most of the month the Moon is a little above or below the Sun's path. Twice each month it crosses it. The point where it crosses going north is the ascending node — Rahu. The point where it crosses going south is the descending node — Ketu.
These two points are not fixed. They slide slowly backwards through the zodiac, completing a full circuit in about 18.6 years. That works out to roughly eighteen months in each sign, always in reverse order.
Why eclipses happen near them
There is a new moon every month, yet the Moon rarely covers the Sun, because it usually passes slightly above or below it. An eclipse needs the Sun, Moon and Earth to line up, and that can happen only when a new or full moon falls close to a node — close to where the two paths actually intersect.
A new moon near a node gives a solar eclipse. A full moon near a node gives a lunar eclipse. The Sun reaches one node or the other about every six months, so eclipses arrive in seasons roughly half a year apart, and most years bring two of each kind.
This is the fact behind the story. In the Puranic account a being named Svarbhanu disguised himself among the gods to drink the nectar of immortality. The Sun and the Moon noticed and raised the alarm; Vishnu struck off his head. Having tasted the nectar, both halves lived on — the head as Rahu and the body as Ketu — and they periodically swallow the two luminaries that exposed them.
How they are read in a chart
Because they are always opposite, Rahu and Ketu form an axis across two houses, and the two are read as a pair. Rahu is appetite: the area of life where a person reaches outward, wants more, and often breaks with convention to get it. Ketu is its counterweight: the area where there is skill but little hunger, and a tendency to let go.
They own no signs. A long-standing rule is that they act like the lord of the sign they occupy and like any planet they sit beside. A second saying holds that Rahu behaves like Saturn and Ketu like Mars. In practice an astrologer reads their sign lord first.
- Rahu rules the nakshatras Ardra, Swati, Shatabhisha, and its mahadasha lasts 18 years.
- Ketu rules the nakshatras Ashwini, Magha, Mula, and its mahadasha lasts 7 years.
Mean node and true node
There are two ways to compute the nodes. The mean node moves at a steady average rate. The true node follows the small wobble in the Moon's orbit and so swings slightly ahead of and behind the mean position — by up to about a degree and a half — and occasionally moves forward for a short time.
Both are in use. Astronaad's chart engine uses the mean node, the more traditional choice. The difference rarely changes a sign, but for a node sitting within a degree or two of a sign boundary the two methods can disagree, which accounts for most cases where two programs place Rahu differently.
Common fears, in proportion
Rahu and Ketu are the grahas most often invoked to frighten people, so some plain facts help. Everyone has them; they are in every chart ever drawn. Rahu Kaal, the daily window named after Rahu, is a convention of timing and not a danger. Kaal Sarp, the pattern in which all the other planets fall on one side of the Rahu–Ketu axis, is a later addition to the tradition whose severity is frequently overstated, and it appears in the charts of many successful people.
Read soberly, the nodes describe where a life pushes forward and where it releases — and their periods are frequently the ones in which people travel, change field or take the risk that defines their career.
Frequently asked questions
- Are Rahu and Ketu real planets?
- No. They are mathematical points — the two places where the Moon's orbit crosses the Sun's apparent path. They have no mass and cannot be seen, but they mark where eclipses occur, which is why they are counted among the nine grahas.
- Why are Rahu and Ketu always opposite each other?
- Because they are the two ends of a single line — the line along which the plane of the Moon's orbit intersects the plane of the Earth's. Two points on opposite ends of a line through the Earth are always 180° apart.
- How long do Rahu and Ketu stay in one sign?
- About eighteen months. They complete a circuit of the zodiac in about 18.6 years, moving backwards through the signs.
- What is the difference between Rahu and Ketu?
- Rahu is the ascending node and signifies desire, ambition and worldly pursuit. Ketu is the descending node and signifies detachment, insight and release. They are read as two ends of one axis.
- Why do different apps show Rahu in different places?
- Usually because one uses the mean node and the other the true node. The two can differ by up to about a degree and a half, which matters only when Rahu is very near the boundary of a sign or nakshatra.
Work it out for yourself
These tools compute what this guide explains, from real astronomical positions.
- Kundli →The house axis Rahu and Ketu occupy in your chart.
- Dosha & Remedies →Checks the Kaal Sarp pattern, with its type and severity.
- Rahu Kaal Today →The daily window named after Rahu, for your city.
How this guide was written
The reference tables on this page are generated from the same data Astronaad’s calculators run on, so the guide and the tools cannot disagree. Where classical authorities differ, the text says so and names the convention Astronaad follows. Astrology is a traditional system of interpretation: nothing here is medical, legal or financial advice. Spotted an error? Tell us.