In India, astrologers from different schools use various ayanamshas—slightly different values from one another. Although this difference is small, it can significantly affect subsequent calculations. The most widely used and authoritative is the Lahiri ayanamsha. Its values are listed below:

Lahiri Ayanamsha on 1 January of Each Year (20th Century) & First 10 Years of the 21st Century

To calculate the ayanamsha for any given date, you interpolate between two known values. For example, someone born in Leningrad on 7 October 1973 at 18:00. The ayanamsha on 1 January 1973 is 23°29′04″, and on 1 January 1974 is 23°29′55″. First, you find the monthly shift (difference ÷ 12), then multiply it by 9.23 months (nine months and seven days to the birthday), and add that to the 1 January 1973 value. The result: 23°29′43″.

Calculating Planetary Coordinates

To compute planetary positions, you need reference materials available in any astrology shop:

Ephemerides, A gazetteer of city coordinates and time zone changes (for the CIS region).

In India, astrologers use Panchangas—yearly guides based on the sidereal zodiac—instead of ephemerides based on the tropical zodiac. You also need to know the precise ayanamsha for the birth date.

First, use the ephemerides to find the positions of the planets in the tropical zodiac, then convert them to sidereal by subtracting the ayanamsha. Ephemeris data is given for 00:00 Greenwich Mean Time (GMT). To get positions at the actual birth moment, convert local birth time (Tₛ) to GMT time (Tₑ𝚐):

Tₑ𝚐 = Tₛ − N − 1

Where:

N is the local time zone offset, 1 is the decree-hour adjustment (used after 31 March 1930 in this country), Subtract daylight saving if born after 1981 in summer.

In our example:

Tₑ𝚐 = 18:00 − 2 h − 1 h = 15:00 GMT.

Coordinates are calculated for 15 h GMT. Next, note the planetary positions for 7 and 8 October:

Example: Sun’s Coordinates

7 October: 13°35′00″ Libra 8 October: 14°34′12″ Libra

To interpolate for the birth moment:

(14°34′12″ − 13°35′00″) ÷ 24 h × 15 h + 13°35′00″ = 14°13′54″ Libra

Now convert to sidereal by subtracting the ayanamsha:

14°13′54″ − 23°29′43″ (adding 30° of Virgo because the result is negative) = 20°44′11″ Virgo

Thus, in Vedic astrology, the person is born under the sign of Virgo.

Planets Mercury to Ketu

You calculate the coordinates for Mercury, Mars, Jupiter, Saturn, Venus, Rahu, and Ketu in the same manner.

Note on retrograde Mars: In ephemerides it is marked “R.” For a retrograde planet, subtract the smaller coordinate from the larger, calculate its motion up to birth time, then subtract the ayanamsha:

True Mars position:

[Difference over time] − ayanamsha = 13°29′17″ Aries

Note on the Moon: Because the Moon moves quickly, ephemerides list two values—0 h and 12 h GMT. If birth occurs between these, you interpolate using 12 h, not 24 h. In our example:

(24°53′ − 17°49′14″) ÷ 12 h × 3 h + 17°49′14″ = 19°22′10″ Aquarius

Subtract the ayanamsha:

19°22′10″ − 23°29′43″ = 25°52′27″ Capricorn

Thus all nine planets’ sidereal positions are obtained.

Planets & Zodiac Signs

As planets traverse the twelve zodiac signs, they express different qualities. This is because each sign is ruled by a planet, and some planets are stronger (exalted) or weaker (in fall) in particular signs. The qualities of planets in signs emerge from their relationships and status within those signs.