Astronomical Differences between Western and Vedic Astrology

Around 285 AD The tropical (Western), and the Vedic Aries were on the same zodiacal plane. But due precession of the equinoxes, today at present, there is approximately a 24° difference between the two.
Therefore all the planets including Ascendant (Lagna) shows a difference of 24° approx.

The basic difference between the two systems

Sr. No.	Indian /Vedic Astrology	Western Astrology
1	Vedic zodiac is Sidereal	Western Zodiac is Tropical
2	In Sidereal astrology, the zodiac is aligned with 27 constellations, or Nakshtra groups. Aries, the first sign of the zodiac, aligns with the first Nakshtra, called Ashwini.	In the tropical zodiac, the point in space when the Sun crosses the earth’s equator is the beginning point of the zodiac or 0°Aries.
3	The Vedic system basically applies the same position of the planets as used by astronomers against the background of Nakshtra.	Western astrology is based on the orientation of the Earth to the Sun.  It “assumes” that every year, the Sun at the spring and autumnal equinoxes is at the first degree of Aries and Libra respectively, and at the first degree of Cancer and Capricorn at the summer and winter solstices.  As a result of this fundamental assumption, the tropical zodiac ignores an astronomical event called the Precession of the Equinoxes.
4	Under Vedic system, the Sun is in Aries from 13th April to 14th May – a difference of 22 days.	According to western astrology the Sun is in the sign of Aries from 21st March to 20th April.
5	Vedic Astrology uses nine Grahas viz. Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn and the two nodes of the Moon called Rahu and Ketu.	Western Astrologers also use these nine Grahas but they use Uranus, Neptune and Pluto – as well as their moons and some of the largest asteroids, when interpreting horoscopes In addition.
6	Sidereal astrology can be called “Cosmic astrology” for it measures the relationship of the fixed stars and the solar system to ourselves.	Tropical astrology is largely “Sun” based, for the signs of Aries, Taurus, Gemini etc. may more accurately be called “solar houses”.
7	Vedic astrologers may also apply these systems, but their primary system is the use of planetary periods, called Dashas.  There are 32 such systems outlined by Parashara in his treatise Brihat Parashar Hora Shashtra.	Western Astrology uses progressions and transits (the position and movement of the planets on a given day.).