Rasi

To say where a graha (planet) stands, Jyotish needs a ruler laid around the sky. That ruler is the zodiac, and a rasi (sign) is one twelfth of it.

The zodiac

Seen from the Earth, the Sun, the Moon and the other grahas all keep to a narrow band of the sky. Measured along that band, a full turn is 360°, and the zodiac is that circle with a point chosen as its start, 0°.

Two choices of starting point are in use. The sayana (tropical, moving) zodiac starts where the Sun stands at the March equinox. That point is not fixed among the stars: it slips backward against them by about one degree in 72 years. The nirayana (sidereal, fixed) zodiac starts at a point tied to the stars, so it stays put. Jyotish uses the nirayana zodiac, and so does hora.

The gap between the two starting points is the ayanamsa. It grows slowly, and astrologers disagree slightly on its size, because they disagree on which star marks the start. The Ayanamsa field on the home page chooses among the common schools; the chart page prints the value it used.

Longitude

A graha's longitude (sphuta) is how far along the nirayana zodiac it stands, as seen from the Earth: from 0° up to just under 360°. Each degree has 60 arcminutes (′), and each arcminute 60 arcseconds (″). The lagna (ascendant) has a longitude too, and so does every other point a chart holds.

The twelve rasis

Cut the zodiac into twelve equal parts of 30° and each part is a rasi. They follow one another in a fixed order, starting at 0° with Aries. Each has an English name, a Sanskrit name and a two-letter symbol; hora shows the English name, and the book writes the symbol in its shorthand for longitudes. The table gives the same facts as the book's Table 1.

Writing a longitude

A longitude such as 256°31′ says little until you know its rasi. Two short forms put the rasi in.

• Degrees in the rasi: the degrees counted from the start of the rasi, the rasi's symbol, then the arcminutes. Our example below is written 16 Sg 31: 16°31′ into Sagittarius.
• Completed rasis: how many whole rasis lie behind the point, an s, then the degrees and minutes into the next one. The same point is 8s 16° 31′: eight rasis complete, Aries to Scorpio, and 16°31′ into the ninth, Sagittarius.

To turn either form into a longitude, multiply the number of completed rasis by 30° and add the degrees inside the rasi. To go back, divide the longitude by 30°: the whole number is the count of completed rasis, and what remains is the degrees inside the next rasi. Both short forms stop at the arcminute; the seconds are cut off, not rounded, just as in the chart.

A worked example

On 1 January 2000 at 12:00 UT, at Greenwich, hora places the Sun at 16°31′17″ in Sagittarius (see the chart).

1. Sagittarius is the ninth rasi, so eight are complete before it: 8 × 30° = 240°.
2. Adding the degrees inside Sagittarius gives the longitude: 240° + 16°31′17″ = 256°31′17″.
3. In short form, that is 16 Sg 31, or 8s 16° 31′.
4. Back again: 256°31′17″ divided by 30° is 8, with 16°31′17″ left over, so the Sun is 16°31′17″ into the ninth rasi.

The chart used the Lahiri ayanamsa, which it prints as 23°51′25″; on the sayana zodiac, the same Sun would stand that much further on.

In the chart

The chart page's table gives each graha's rasi and, in the Degree column, its degrees inside that rasi: the first short form, with the seconds kept. Each rasi name there links to this page.

Next comes the bhava: the rasis counted from a chosen point of the chart.

Book reference: P.V.R. Narasimha Rao, Vedic Astrology: An Integrated Approach, chapter 1, § 1.3.2. Where to get the book