Tropical or Sidereal Astrology?
The main difference between Tropical (or Western) and Sidereal (often known as Vedic) Astrology systems is where the 12 signs of the zodiac are referring to.
Sidereal or Vedic systems of astrology look at where the planets are moving through the actual constellations of the 12-sign zodiac;
Tropical Astrology links the zodiac sign to the seasons — the movement of the Sun at the solstices and equinoxes through the year.
In this fashion, in the northern hemisphere, the Spring (Vernal) Equinox is the moment where the length of day and night is equal in the spring season, and marks the beginning of the sign of Aries.
However, due to the earth’s wobble on its axis and the precession of the equinoxes, on that same day of the Vernal Equinox, the position of the Sun will not always be pointing towards the Aries constellation. There was a time when the positions of the Tropical and Sidereal zodiacs overlapped and aligned around 285 AD. The Vernal Equinox point moved from Aries to the Pisces constellation in the 1st century BCE, and will continue until the 26th century, at which point it will move into the Aquarius constellation.
All this is to say, some astrologers practice Vedic Astrology, and others practice Tropical Astrology. They are both valid! One is not right or better than the other.