Rasi chart and navamsa chart: what the D9 adds to your jathakam

Each sign cut into nine parts

A sign is 30° wide. The navamsa divides it into nine equal parts of 3°20' each, and every part is given a sign of its own. A planet is placed in the navamsa sign of the part it occupies. So a planet at Cancer 10°51' has two addresses: Cancer in the rasi chart, and the sign that part 4 of Cancer carries in the navamsa chart.

Three degrees twenty minutes is also exactly the width of a pada, the quarter of a nakshatra (27 nakshatras of 13°20', each in four padas). Twelve signs times nine parts, or 27 nakshatras times four padas, both give 108 slices, and they are the same slices. That gives a shortcut: number the nakshatras 1 to 27 and the padas 1 to 4, and the navamsa sign counted from Aries (Aries = 0) is (4 × (nakshatra number − 1) + pada − 1) mod 12. The example Moon is in Pushya (8), pada 3: 4 × 7 + 2 = 30, and 30 mod 12 = 6, which is Libra.

Where the count starts

The nine parts of a sign do not all start from Aries. The first part takes the sign that begins the same element, and the rest follow in zodiac order.

If you prefer a formula, take the sidereal longitude L in degrees from 0° Aries, multiply by 9, divide by 30, drop the fraction, and keep the remainder after dividing by 12. The result counts signs from Aries: 0 Aries, 1 Taurus, up to 11 Pisces. For the Moon, L = 100.859°, so 100.859 × 9 ÷ 30 = 30.26, which becomes 30, and 30 mod 12 = 6: Libra again. The table and the formula must agree, and they do.

Worked conversions, planet by planet

Three by hand first. In each case divide the degrees within the sign by 3°20' (3.333°), round up to get the part, then count from the starting sign.

1. Moon, Cancer 10°51'. 10.85 ÷ 3.333 = 3.26, so part 4. Cancer is water and counts from Cancer: Cancer, Leo, Virgo, Libra.
2. Lagna, Leo 5°38'. 5.63 ÷ 3.333 = 1.69, so part 2. Leo is fire and counts from Aries: Aries, Taurus.
3. Venus, Gemini 20°56'. 20.93 ÷ 3.333 = 6.28, so part 7. Gemini is air and counts from Libra: Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces, Aries.

The whole chart, with the same method:

The navamsa lagna is the sign of the lagna's own navamsa, here Taurus, and the houses of the D9 are counted from it exactly as in the rasi chart, in whichever South or North Indian style you draw it. The calculator does this conversion for every point and shows the result both as the second chart and in the Navamsa column of the planet table. In the D9 above, Sun and Ketu share Pisces and Jupiter and Saturn share Gemini.

Vargottama: the same sign in both charts

When a planet's rasi sign and navamsa sign are the same, the planet is called vargottama. It happens only in one fixed slice of each sign type:

No planet in the Chennai example qualifies; the calculator marks a vargottama planet with a badge in the planet table. In a chart drawn for Kochi at noon, Jupiter at Aries 1°28' does: Aries is movable, 1°28' is inside the first 3°20', and the D9 sign is Aries again. Traditional texts treat a vargottama planet as steady and well placed; I treat it as a useful marker that the two charts agree, not as a promise of anything.

Why the navamsa needs an accurate birth time

The rasi lagna stays in one sign for roughly two hours. The navamsa lagna changes nine times in that span, so each part lasts only 13 or 14 minutes. For the Chennai example on the day of birth, the lagna is in Leo from 06:06 to 08:09 local time:

A birth recorded at 06:30 is Taurus in the D9. Write 06:35 by mistake and it becomes Gemini. The hospital slip rounded to the nearest five minutes is the usual culprit, and so is a clock that ran fast.

The planets can be just as touchy. In the Kochi chart the Moon is at Libra 16°42', only two arc-minutes past the boundary at 16°40'. The Moon covers about half an arc-minute per minute of time, so a birth about five minutes earlier would put it at the end of part 5, and its navamsa would be Aquarius instead of Pisces. My working rule: if the birth time is uncertain by more than ten minutes, trust the rasi chart and treat the navamsa lagna and any planet within a few arc-minutes of a part boundary as provisional. If there is no birth time at all, the calculator shows the Moon chart only and does not invent a lagna.

How the two charts are read together

Astrologers read the rasi chart first, for the lagna, the houses and where each planet stands. The navamsa is then consulted for the planet itself: which sign it falls in there, and whether that sign is its own, a friend's or an unfriendly one. Many practitioners also look at the D9 lagna and the placement of the lord of the partnership house in partnership questions. These are conventions of the tradition and schools differ in how far they take them. The calculator does the arithmetic; the interpretation remains with the reader.

For the timing side of a chart, the Vimshottari dasa balance and the running period are worked out from the same Moon degree you used in the table above, without the navamsa.