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Placidus houses

Placidus divides the time taken by zodiac degrees to cross the sky, producing unequal houses. Mạghā calculates its cusps for D1 and uses them in KP. The Ascendant begins the first house; the Midheaven begins the tenth.

Twelve cusps, six pairs of equal spans

Placidus cusp positions and spans
House pair	First cusp	Opposite cusp	Span
1 / 7	Libra 0°45′38″	Aries 0°45′38″	29°45′41″
2 / 8	Scorpio 0°31′19″	Taurus 0°31′19″	29°18′39″
3 / 9	Scorpio 29°49′58″	Taurus 29°49′58″	29°29′37″
4 / 10	Sagittarius 29°19′35″	Gemini 29°19′35″	30°34′45″
5 / 11	Capricorn 29°54′21″	Cancer 29°54′21″	31°08′47″
6 / 12	Pisces 1°03′07″	Virgo 1°03′07″	29°42′31″

Lahiri frame. The 1st / 7th are the Ascendant / Descendant; the 4th / 10th are the Nadir / Midheaven. The shortest houses are 2 and 8; the longest are 5 and 11.

Each cusp marks a third of a degree's journey above or below the horizon

A degree's semi-arc is the time it takes to rise from the eastern horizon to the meridian. Placidus makes the 12th cusp the degree that has covered one third of its semi-arc and the 11th cusp the degree that has covered two thirds. Below the horizon, each degree's night semi-arc is divided the same way for the 2nd and 3rd cusps, and the other six cusps lie exactly opposite.

Semi-arcs change with the latitude of birth and with each degree's distance from the celestial equator, so Placidus houses stretch and shrink. For Nila Raman born in Bengaluru at about 13° north, they run from 29°18′39″ for the 2nd and 8th houses to 31°08′47″ for the 5th and 11th. Farther from the equator the spread grows much wider.

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KP reads each Placidus cusp as the exact start of a house

K. S. Krishnamurti (1908–1972) surveyed the house systems of his day, from Porphyry's to Regiomontanus's, and settled on the Placidus semi-arc system, the method then in common use, working from Raphael's Tables of Houses. A cusp, he wrote, is the exact point where a house begins, and the house extends to the next cusp.

That reverses Śrīpati's bhāvas, where an angle marks a house's middle. KP judges each house through the sign lord, star lord and sub lord of its cusp, so a few minutes of arc can change the reading. Raphael's tables give tropical cusps, so KP subtracts its ayanāṁśa from them.

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Mạghā lists Placidus cusps in the Bhāva tab and uses Placidus for every KP reading

Choose Placidus in Bhāva to compare changed planetary houses and each cusp, next cusp and span. Bhāva Bala evaluates these houses at their cusps. This view uses your chart ayanāṁśa; KP always uses Krishnamurti's.

Beyond roughly 66°34′ latitude, Swiss Ephemeris substitutes Porphyry because Placidus cannot be calculated. Bhāva and chart drawings identify the fallback, but the KP tab still labels those cusps Placidus. Nila’s chart has no planetary house changes.

Why the cusp sign changes

Nila’s KP cusps are 5′49″ ahead of her Lahiri cusps because Krishnamurti’s ayanāṁśa is smaller. The fifth and eleventh move from Capricorn/Cancer 29°54′21″ to Aquarius/Leo 0°00′09″. The eleventh cusp’s ruler changes from Moon to Sun, but planets retain their houses because both planets and cusps shift together.

What people ask about Placidus houses

Why are Placidus houses unequal in size?

Placidus divides time rather than the zodiac. Each cusp marks the degree that has covered a set fraction of its path between the horizon and the meridian, so the houses take equal shares of time, and their sizes in degrees depend on how fast the signs rise at your latitude. Near the equator the twelve houses stay close to 30° each; the farther north or south of it, the more unequal they become.

Is Placidus used in Vedic astrology?

Placidus comes from Western astrology, where it carries the name of a 17th-century monk. Classical Jyotiṣa texts do not use it; they count houses by signs or by bhāvas such as Śrīpati's. In India it is used above all in KP. With the sidereal zodiac, its cusps are the tropical cusps less the ayanāṁśa, which is how Mạghā calculates them.

Why can't Placidus houses be calculated near the poles?

Placidus needs each degree's time above the horizon. Inside the polar circles, beyond about 66°34′ north or south, some degrees never rise and others never set, so they have no semi-arc to divide. Swiss Ephemeris then returns Porphyry cusps, which split each quarter between the angles into equal thirds. For a birth in Tromsø, at 69°39′ north, that happens at any hour.

Placidus or whole sign: which should I use?

They divide the sky differently. Whole-sign houses make each sign one house, counted from the Lagna's sign. Placidus starts the 1st house at the Lagna's degree and sizes houses by time, so a planet in the Lagna's sign but before its degree falls in the 12th. Parāśari astrologers often count whole signs, while KP astrologers use Placidus. For Nila both give the same houses.