As per Jyotisa a Yoga is given rise to when one planet, sign or house is related to another of the same kind or different kind by way of placement, aspect or conjunction. It is the active consideration of planetary yogas and the active consideration of the planetary Dashas i.e. directional effects, which are the two most important factors that distinguish Hindu astrology from Western astrology.
Laghu Parashari is the concise main version of the predictive side of the Hora Shastra, and the Parashari System is most widely followed, having stood the test of time and because it is simple and unambiguous. The ancient Hindu astrologers seem to have confined their exercises to the seven planets – the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn; Rahu and Ketu, these two that are mathematical points, are referred to but rarely. Parashara also refers to five more Chayagrahas which are all actually invisible mathematical solar positions but having impact on the life of individuals and nations. The Rigveda does refer to the total of thirty-four, comprising twenty-seven Nakshatra-divisions of the Zodiac and the seven planets which was the general format then in use. However, elsewhere it also refers to the total of forty-nine by adding to the said thirty-four the two Chayagrahas (the lunar nodes), the twelve rasis (signs) and the Ayanamsa. Varahamihira favoured Satyacharya’s Dasha system though he says many had spoiled it by useless multiplications but Satyacharya did not deviate from the basic Parashari principles. Because of there being nine active planets and equally active twelve signs (including their numerous sub-divisions) and twenty seven nakshatra divisions, yoga-formations are unavoidable.