Vedic Astrology is an ancient Indian science which explains planetary motion and position with respect to time and its effect on humans and other entities on earth. Vedic astrology can be traced back many thousands of years. Early Vedic astrology was only based on the movement of planets with respect to stars, but its later day version included zodiac signs as well. According to Vedic astrology there are 27 constellations made up of 12 zodiac signs, 9 planets and 12 houses. Each house and planet represents some special aspects of human life. Depending on the date, time and place a person is born, the 12 signs are distributed among the 12 houses and 9 planets are placed in various houses accordingly. This visual representation of the signs and planets is called a horoscope chart. Vedic astrology interprets the meaning of this arrangement.

Vedic Astrology (Jyotisha) has three main branches:
. Siddhanta (Astronomy): Astronomy & its application to astrology
. Samhita (Mundane astrology): Covers Mundane astrology, predicting important events related to countries such as war, earth quakes, political events, astro - meteorology, financial positions, election astrology; house & construction related matters (Vaastu Shaastra), animals, portents & omens etc.
. Hora (Predictive astrology): This branch has many different styles / sub branches. We encourage you to ask Prashna (question). Predictions are based on the time when a question is asked by a person.

Source: http://www.vedicscholar.com/about_vedic_astrology.php