Zodiac or celestial circle is assumed to be a fixed one.The Indian system uses mathematical models and makes it possible to calculate, analyze and interpret to the desired level of accuracy progressively.
The Western or Sayana or Moving zodiac system makes calculations and predictions based on the so-called present position of the stellar system. This has limitations as in the present scientific world, there is no way of defining the current position of ever moving celestial body zodiac.
The difference between Sayana longitudes and Nirayana longitudes of planets is called "Ayanamsa" or precision. Sayana system is at best a crude first order approximation. Nirayana system is an innovative solution to a complex situation.
The Sayana system uses techniques of approximation and progressive accuracy in predictions is not possible.
When we compare the Indian Astrology with that of the Western Astrology there are certain general principles found in both the systems. Ownership of houses, exaltation, debilitation, characteristics of planets and the 12 aspects of human life are the same.
In certain other aspects they differ from each other. For example the square opposition aspects are bad and trine and sextile aspects are always good in Western Astrology. Where as in the Hindu system good and bad aspects are not based on the types of aspects, but by the nature of the planets involved in the aspects. Ashtakavarga system, Shadvarga charts, Shadbala assessment and Yogavali are not found in the Western System.
The Indian Science of Astrology also gives certain remedial measures to overcome mental, moral and physical sufferings by means of medicinal roots, mantras and yoga practices and Gemstones. Though Hindu Astrology deals with all the aspects of human life indicating materialistic success and failures, it is deeply rooted in philosophy.
12 Zodiac signs with Indian and Western Astronomical names
The Sayana system of generic predictions is based on Sun signs. The sun sign is closely related with the date of birth. In contrast, calculation of moon sign is more complex and cannot be determined with simple dates from the Gregorian calendar.
Vedic Indian astrological system uses many more complex calculations. The Lagna, Birth Star and several other parameters relating to each individual is determined by processing the horoscope for the specific date and place of birth. For instance, the branch of Vedic Indian astrology dealing with only Muhurtams or determining auspicious time for doing any important activity is followed extensively for starting important activities. Like wise, marriage compatibility is a separate branch in Indian astrology and many parameters dealing with compatibility of prospective groom and bride are analyzed. All these subsystems in Indian Astrology are based on complex calculations from birth particulars.
Predictions based on Vedic astrology are more accurate and specific than those based on sun sign or moon sign. All these sign based predictions are generic. For example- using Nirayana Sun Signs, all persons born between 15/2 to 14/3 fall into the sign of Aquarius. They would have a certain set of traits or characteristics. However, while using moon signs two persons though born on 15/2 in the same year but at different times may have different birth stars. Predictions based on Vedic astrology are accurate. Here Lagna is first determined. Further Lagna varies in every two hours and also with place of birth. This gives very different, traits/personalities and unlike Sun signs makes it possible to categorize the traits of every individual in depth.