The meaning of the Mulatrikona signs
Determine which house — a good one or a bad one — the Mulatrikona sign of the planet that interests you falls into. If the Mulatrikona is in a good house (in other words, not in the 3rd, 6th, 8th or 12th) and the planet itself is also favourably placed relative to its own sign, the results will be positive. In the opposite case undesirable effects will take place.
When the Mulatrikona sign falls into a bad house, but its lord has chosen a good place for itself as seen from the Mulatrikona, the consequences will be unpleasant. However, when a planet is badly placed relative to the sign of its Mulatrikona, which is itself well placed, the results will likewise be unfavourable.
For example, for a rising Sagittarius, Saturn brings excellent fruits when it occupies the 5th house: its Mulatrikona sign (Aquarius) falls into the 3rd house from the Lagna, which is considered unfavourable, while Saturn itself is in a bad place from the evil 3rd house. By this same principle, the placement of Mars in the sign of Scorpio for an Aries Lagna does not form a productive yoga.
Sri Govind Swarup Agarwal — «Vedic Astrology»
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The Mulatrikonas of the planets
Mulatrikona translated literally means «the root third».
The Mulatrikonas are special areas in which the qualities of a planet manifest very beneficently and only a little more weakly than in exaltation. For most planets the Mulatrikona covers a portion of the positive domicile. For the Moon, however, this portion is placed in the sign of exaltation, for the Moon has no positive domicile (a domicile with an odd number). And for Mercury the Mulatrikona is placed in Virgo, which is at once both the domicile and the sign of exaltation of this planet.
The signs and degrees of the Mulatrikona of the planets
The Sun 0°—20° of Leo
The Moon 3°—20° of Taurus
Mars 0°—12° of Aries
Mercury 15°—20° of Virgo
Jupiter 0°—10° of Sagittarius
Venus 0°—15° of Libra
Saturn 0°—20° of Aquarius
The Mulatrikona sign for Rahu is Aquarius.
The Mulatrikona sign for Ketu is Scorpio.
What svakshetra is, is easier to explain by an example: the Sun in Leo, but in the degrees not from 0—20°, as in the Mulatrikona, but from 21 to 30° (that is, the remaining 10°). Svakshetra is considered favourable, but yields a little to the Mulatrikona in strength. Svakshetra is translated as «one’s own field», that is — one’s own sign.