What is Ketu?

Ketu is the descending lunar node, the crossing where the Moon slips back below the ecliptic after its northern half of the orbit. It never appears alone. Ketu stands exactly 180 degrees from Rahu, in the opposite sign and at the identical degree and minute, so software rarely calculates it separately and simply mirrors the other node. Every Vedic chart in Moon Shine AI lists it among the nine grahas, always facing Rahu across the wheel.

Three mansions, evenly spaced around the circle

Ketu rules Ashwini, Magha and Mula. Look at where those three begin and a pattern jumps out. Ashwini opens at 0 degrees of sidereal Aries, Magha at 120 degrees, Mula at 240. They divide the zodiac into exact thirds, because the nine planet rulership cycle of the nakshatras runs three complete rounds and Ketu opens every one of them.

That structural position carries into the timing system. The Vimshottari list is conventionally recited starting from Ketu, and anyone born with the Moon in one of those three mansions begins the lifetime sequence in a Ketu mahadasha. The period runs 7 years, tied with Mars for the shortest of the nine.

A short opening period has a practical consequence worth noticing. Charts that start under Ketu move into the 20 year Venus mahadasha early, often before adulthood, which changes the whole rhythm of how the sequence unfolds compared with a chart that opens under Saturn or Venus.

Banner, comet, tail: what the word carried

Ketu in Sanskrit means a banner or a flag, and older astronomical writing used it for comets and for bright irregular appearances in the sky. Texts speak of many ketus rather than one. The narrowing of the word to a single lunar node happened later, as the nine graha scheme settled into the form used today.

The narrative side inherits from the same churning of the ocean account that gives Rahu its head, with Ketu taking the remainder below the cut. That is where the common description of Ketu as the tail comes from. It is a story about why the two ends belong to one figure, not a description of any mechanism.

Classical sources also give Ketu the title moksha karaka, the significator of release. The phrase belongs to the tradition and is worth quoting as the tradition's own framing rather than as an independent finding. What it points at, in practice, is the habit of reading Ketu as the place where a chart lets go of something rather than reaches for it.

How the tradition reads the placement

Where Rahu is read as appetite, Ketu tends to be read as narrowing. The house it occupies often gets described as an area where competence arrives early and interest arrives late, where you already know the moves and feel oddly unmoved by the results. That is a description of emphasis, not a forecast of what happens there.

Because the two nodes sit on one axis, most Vedic astrologers refuse to read either in isolation. A Ketu in the fourth sign from the lagna automatically puts Rahu in the tenth, and the pair is discussed as a single tension between a familiar side and an unfamiliar one. Reading only the half you find interesting produces half a picture.

Popular writing overshoots here more than almost anywhere else in Vedic astrology, turning a placement into a verdict about renunciation or loss. The measured version keeps two limits in view. A node describes an emphasis in the chart, and no placement in any system carries the authority to say what a life will contain.

What to check before you trust the position

Since Ketu is derived from Rahu, every calculation question about Rahu passes straight through to it. If the chart used the mean node rather than the true node, both ends inherit that choice. If the two versions disagree enough to move Rahu across a sign boundary, Ketu crosses one at the same instant, in the opposite direction.

The sidereal frame adds its own offset. Ketu and the Western South Node mark the same crossing, but the Vedic chart applies the ayanamsha before naming the sign, which usually shifts the placement back by one. Someone reading both traditions will see two different sign names for one point, and neither is a mistake.

One last detail catches people out. Nakshatra boundaries fall every 13 degrees 20 minutes, so a node near an edge can be listed in different mansions by two pieces of software using different ayanamsha values. Where the mansion matters to the reading, the underlying degree is the thing to check.