The strength of a planet is determined in two ways.
1) Aawasia bala (Residential strength) and
2) Shadbala (six types of balas).
The strength of a planet is measured in units called Rupa. 1 Rupa is equal to 60 shashtiamsas.
AAWASIA Bala: This is the strength attained by a planet by virtue of its placement in a bhava in horoscope. The longitudinal length of a bhava is not exactly 30 degrees, but varies. The beginning of bhava is called Bhava Aarambha sandhi and the end of the bhava is called Bhava Virama sandhi. The mid pint of the bhava is called Bhava Madhya or Mid cusp of bhava. At the Aarambha sandhi, planets get 0 shashtiamsas or 0 Rupa. The strength increases as it moves towards mid cusp and attains 1 Rupa or 60 sh at Mid Cusp. As it moves from MC to Virama Sandhi again the strength decreases and at Virama sandhi the strength is 0 Rupa. The strength of the planet situated in between is calculated proportionately.
SHADBALA: The strength of 7 planets are calculated in this method and Rahu & Ketu are not taken into account. There are six types of Shadbalas. They are
- Sthaana bala – Positional strength
- Dig Bala – Directional strength
- Kaala Bala – time strength or temporal strength
- Chesta Bala – Motional strength
- Naisargika bala – Natural strength
- Drishti Bala or Drig Bala – Aspectual strength