What Sukuyō astrology is
Sukuyō divides the Moon's roughly twenty-seven-day circuit of the sky into twenty-seven equal mansions, and reads a person's disposition and relationships from which mansion the Moon occupied at birth. It reached Japan in the early Heian period, in the Sukuyōkyō that Kūkai brought back from Tang China. It was carried forward by esoteric Buddhist monks alongside calendrical work, and was used in court society for choosing dates and judging compatibility.
Each of the twenty-seven divisions is a mansion, and the one the Moon occupied at the moment of birth is the honmyōshuku — the birth mansion. The names — Rō, I, Bō and so on — are Chinese asterism names, and behind them stand the older Indian nakshatras. Sukuyō is therefore not a native Japanese invention but a system that travelled from India through China and settled in Japan.
Are the mansions and the nakshatras the same thing?
As a framework, yes. Jyotish divides the ecliptic into twenty-seven nakshatras, each spanning 13°20′ of longitude. A sukuyō mansion has exactly the same width and the same ordering. This page shows the corresponding nakshatra name alongside your mansion because the relationship is not a resemblance — it is one division carrying two names.
The interpretive traditions, though, diverged. Sukuyō developed its own approach in Japan, reading relationships mainly through the distance between two mansions. Jyotish reads the mansion alongside the ascendant, the placement of the nine grahas, the twelve houses, and the dasha periods. Both start from the same twenty-seven divisions, but they work with different amounts of information.
Why your mansion may differ from other sites
Most sukuyō sites assign the mansion from the lunar-calendar date. That is convenient and correct on most days. But the Moon crosses one mansion in roughly a day, so for a birth falling near a mansion boundary the date alone cannot decide it. A few hours' difference in birth time genuinely changes the answer.
This page does not use the lunar calendar. It computes the Moon's actual sidereal longitude at your birth moment from the Swiss Ephemeris and divides by 13°20′ to find the mansion, using the Lahiri ayanamsa for precession. Births near a boundary therefore resolve correctly. That precision is why the page asks for a birth time.
If your birth time is unknown the mansion can still be approximated, but a boundary day remains possible. The practical approach is to calculate using noon as a placeholder and consider both adjacent mansions. Establishing the birth time itself is separate work, offered as a consultation.
What the mansion can and cannot tell you
The mansion describes tendencies bound to the Moon's position. The Moon is taken to govern the movement of the mind, the speed of reaction, and how a person finds ease; the mansions sort that quality twenty-seven ways. The ruling planet and the gana — the threefold deva, manushya and rakshasa classification — are the classical refinements of it.
Honestly, though, more is invisible from the mansion than visible. Questions about suitability for work, the timing of marriage, or points of caution in health cannot be answered without the other planets and the dasha period currently running. Two people sharing a birth mansion do not share a life, and that is why.
- The mansion follows from the Moon's position alone, and is settled by date and time of birth
- Relations between mansions are derived mechanically from the distance between them
- Judging specific timing requires the dasha periods and current transits