Your query is a common doubt raised by many rational individuals and invariably by non-believers of god. Nothing wrong in having difference of opinion.
Possibly, you may be aware that “Astrology” is a part & parcel of Veda, which is true.
Yes, exact time & spatial coordinates of birth (real time of disconnecting umbilical chord-natural & C-section Birth or exit of head or complete baby) are prime parameters for calculations. Most likely, the present day calculations of horoscopes takes care of conceiving / womb duration. Medically, within 72 hrs of conjugation the union of egg & one sperm may take place. Again, it’s “Probability Theory”. In mathematics & Probability, we say an event (here creation start) can occur with 99%, 96% or 90% confidence level. So, there is nothing called 100% confidence and therefore the Astrology predictions too vary between lesser to highest possible confidence and never can have 100%. Main reason is the number of parameters an astrologer considers for calculations and his knowledge plus skill to interpret so many variables, their feasible combinations. Therefore, we can blame ourselves (like going to LMP Doctor, RMP, MBBS, MD, super-specialist for any ailment and blaming him for killing the patient: Affordability & Requirement) for mid-prediction. Atleast, I won’t agree or say “True Vedic Astrologer does prediction for only money”. Ample dakshinai was given to pandits, gurus, Acharyas, Brahmins without asking earlier and now a days without baby’s crying even mother’s do not feed milk. So, survival instinct of every astrologer has forced him to say pleasing predictions with ifs & buts, pariharams, etc. Infact, as a citizen and practicing a profession.... continued
Infact, as a responsible Citizen & practicing a profession to earn our livelihood can majority (exceptions never proves the rule) say “I do not lie, I am cent % honest & true to my employer, employees, even mother, father, wife, family, friend, colleague, 100% involved & Productive in job, journey, availing facilities, IT, etc”. Answer is “NO”. Than how we can expect a day to day basis earning Astrologer? Yes, in Kaliyugam -as per Veda, the person with least little knowledge in any field shall project himself as super specialist in the field. We should be cautious. “Kurai Kudam Vs Nirai kudam...”. Masters & Vedic Pandits, enlightened gurus always keep low profile and tell only truth, whether you like or not. So, with total belief & faith (like we go to a doctor of our affordability & ailments) approaching right person for any particular job in right time is needed and that too happens only if one has divine blessings and divine support is given if one does good selfless deeds in this life in the name of humanity & god.
Please excuse me if the explanation is not convincing. V.Rajagopalan, Bangalore (Retired Professional R&D Scientist- learning & practicing Veda /Upanishadam/Astrology-not for money as passion)