The principles of Astrology, are well founded in the Vedas. "Karma" or one's actions (what you sow, so shall you reap) forms the fundamental basis of Astrology. Even a mere thought is said to trigger a cosmic reaction. Hence, human as well as other lives tend to progress through this spiritual journey by taking on physical forms until they realize the absolute reality (the reasons or the process is too complicated to be discussed here). An Astrologer is someone who delineates an individual's "Karma Phala" (the fruits of our karma) and provides the individual with the necessary spiritual insight/jyoti (light) to steer them towards the absolute reality/truth. Hence, a true Astrologer is one who himself is illumined by understanding the absolute reality (which is why this science can't be quantified or tested).

Jyotish is multi-faceted. "Jathaka" or Horoscopy is one facet of Jyotish that looks at the planetary positions at birth to predict the events in one's life. Muhurtha astrology looks at the quality of time to predict the course of an event started at any specific time. "Prasna" or Horary astrology is another branch that deals exclusively with predicting outcomes of queries. "Nimmitas" or premonitions based on signs/symbols are another way of understanding how events will unfold. "Ganita" or mathematics is yet another branch that deals with the calculations of planetary motions, the reasoning behind these numbers, etc. 

Science and spiritual life has a lot of similarities. Like how energy can neither be created nor destroyed but would take one form to another so is Athma, it can neither be created nor destroyed it takes one form to another. All these changes takes place based on our good deeds and bad deeds - the so called karma. Through astrology a person can be guided through his life-from doing misdeeds thus showing a way for peace & harmony to his Athma.
Planets like all 'matter' possess energy levels. when a person is born at a specific time/place/latitude/longitude on earth-there will be a specific configuration of planetary positions at that exact time-the energy released by this specific configuration of planets will denote his horoscope & predictions for life. However his deeds in the current birth also have its own influence in the happenings of one’s own life. An astrologer considers all the avenues of his horoscope and his deeds and guides him/her towards attaining peace and harmony in their lives………..