Constructing the Sidereal (Vedic) Horoscope

The process of constructing a sidereal horoscope begins with determining the Lagna, or Ascendant — the zodiac sign that was rising on the eastern horizon at the exact moment of birth — as well as calculating its precise degree.

Step 1: Determining the Lagna

Once the accurate coordinates of the nine planets have been calculated (see Chapter 6), the next step is to determine the Lagna. This requires access to the “Tables of Houses” by Placidus or Koch, as well as the geographic latitude and longitude of the place of birth.

To calculate the Lagna, begin by determining Tpl (Placidus Time) using the following formula:

Tpl = Sidereal Time + Tс – N – 1 + D / 15° per hour

Where:

Sidereal Time is found in the first column of an ephemeris for 0:00 GMT for each day Tс is the local birth time in GMT (adjusted for daylight saving time if applicable) N is a time offset (commonly used in some tables) D is the longitude of the birthplace

Example:

If Sidereal Time on the date is 1h 2m, and the next day is 1h 5m 56s:

ΔSidTime = 3m 56s ÷ 24 × birth time (say 15h GMT) + base SidTime = ~1h 4m

Adjust for longitude and time zone, and apply interpolation to determine the exact Ascendant degree.

Step 2: Using the Tables of Houses

Once you have calculated Tpl, use the “Tables of Houses” to find the degree rising at that time for your specific latitude. In the tables, locate Tpl in the left column and find the corresponding Ascendant in the “Asc” column. If Tpl falls between values, interpolate.

Example:

If 4°22′20″ and 8°42′31″ are adjacent values, and Tpl is halfway between:

Asc = 4°22′20″ + (8°42′31″ – 4°22′20″) ÷ 2 = 6°32′25″ Aries

Then subtract the Ayanamsa (e.g., 23°29′43″) to convert from tropical to sidereal zodiac:

6°32′25″ Aries − 23°29′43″ = 13°2′42″ Pisces

Thus, the first house (Lagna) is Pisces; the second is Aries, the third is Taurus, and so on.

Equal House System (Parashara Method)

In Vedic astrology, the Equal House System is used, as proposed by the sage Parashara. The sign containing the Lagna becomes the entire first house, regardless of whether the Lagna is at 1° or 29°. The second house is the next full sign, and so on. This system is highly practical and still widely used.

There’s another system where each house starts at the exact degree of the Lagna, and every house measures 30°, but we will adhere to the traditional Parashara system.

Chart Styles in India

There are two common visual styles for charts in India:

South Indian Style:

Each square represents a sign. The top right square is always Aries, and the signs proceed clockwise. Lagna is marked with a diagonal line or the abbreviation Lg.

North Indian Style:

The top central diamond is the first house, with the sign number written inside (1 = Aries, 2 = Taurus, etc.). Houses proceed counterclockwise. The second house is the triangle on the left, the third is the bottom triangle, etc.

This format is deeply symbolic — houses 1, 4, 7, and 10 (kendras) are traditionally marked with a swastika, a symbol of life force and cosmic order, which moves clockwise. The remaining houses, which represent karmic burdens and dissolution, rotate counterclockwise, representing the cycle of samsara.

Chandra Lagna (Moon Ascendant)

Chandra Lagna is the chart where the Moon’s sign (Janma Rashi) is treated as the first house. This is invaluable when the exact birth time is unknown. But even with known time, Chandra Lagna should always be examined — particularly for predictive work and transits.

If the Moon is stronger than the Lagna in a chart — as determined by Sthana Bala (positional strength), dignity, or planetary influences — then Chandra Lagna becomes the operative chart and should be interpreted as the primary chart.

Building the Chandra Lagna chart is simple:

Place the sign of the Moon as the 1st house. Lay out the remaining houses in sequence. Interpret planetary positions relative to the Moon as you would with the standard Lagna.