Vedic verses Western astrology is a highly complicated and debated topic. Vedic or Indian astrology follows the sidereal zodiac also known as Niryana. In this system, the planetary positions are as seen from earth to-day by taking into account the tilting of the North Pole and making corrections accordingly.
Western astrology follows the tropical zodiac also known as Sayana. It is based on the current position of the planets from a zodiacal point of view or in other words as observed by the satellites.
This has created a 24 degree difference between two different systems. To give an example, according to the western sun signs Sun enters Aries on the 21st of March. However, according to Vedic calculations Sun enters Aries on the 14th of April.
Translating this difference into a birth chart, you will notice a significant difference in the placement and especially the degree of the planets.
In my opinion, Vedic astrology is a much more practical and convincing system, since we are observing planets from the planet Earth and how they are affecting us rather than having a panoramic view of the planets placed in the galaxy.
In Vedic astrology, Main Period is calculated based on the degree of Moon. Since moon changes a sign after around 2 ½ days, it helps in magnifying minute predictions.