Ayanamsha,is the exact longitudinal difference in degrees between the edges of crossing point of celestial(sidereal) and ecliptic(tropical) equator i.e. 24 degree approx ,as we know our earth is rotating through it’s axis and tilted on it’s axis at around 22 to 24 degree . so basically this is the difference between sidereal and tropical astrology ,sidereal means vedic astrology and tropical means western astrology ,the main difference between sidereal and tropical is sidereal(vedic) astrology consider earth axial tilt i.e.
24 degree approx and tropical (western) astrology does not consider this with astrology and we can see in tropical astrology planet is ahed in degree than sidereal astrology , suppose Sun is 1 degree in Aries on 14 april in sidereal astrology then Sun will be at 25 degree at aries on 14 april, it means that sun will be at 21 march in aries on vernal equinox at 0 degree in tropical astrology i.e. sun will be at equator and start moving towards northen hemisphere that is the main difference between vedic and western astrology .
Eventhough the Chitrapaksha/Lahiri aynamsha is most popular aynamsha in vedic astrology ,besides this KP ,Raman(22 degree) are being used ,but the accuracy of Lahiri(24 degree approx) is upto the point and the branch of astrology known as KP astrology (Krishnamurti paddhati) use their own aynamsha that is known as KP aynamsha which is equal to 24 degree .
Nevertheless, the chitra constellation(fixed star or nakshatra) is in 23(deg) 20’ Virgo to 6 deg 40’ Libra so it stretch from 6(deg) 40’ virgro to 6(deg) 40’ libra so the starting point of zodiac will start from 0(deg) of Aries within ashwini nakshatra ,but some disputes are always there are also some consideration that starting point of zodiac is at the end degree of pisces,according to atharvaeda constellation start with kritika nakshatra too, there are lot of scholars working on aynamsha like chirapaksha/lahiri ,and pushyapaksha,despite the fact that we can get accurate and very close result in software like jagannatha hora .
Well we can say vedic astrology is very pure ,accurate as it consider so many deep rooted concept like nakshatra,transit ,vimshottari dasha against tropical astrology mostly consider transit of planets.
However ,there are lot disputes and argument among aynamsha, which is accurate and which is close to accurate ,as we can see lots of celebrity having very rare horoscope and he has been enjoying wealth luxury and comfort ,fame for long time .