The most fundamental difference between western astrology & Vedic Astrology is the zodiac. In western astrology, Aries begins when Earth crosses the vernal equinox point (which means the first day of spring in the northern hemisphere). But Vedic Astrology uses fixed background stars, or constellations, to determine the position of Aries.
1,500 years ago these two zodiacs were identical, but over time the seasonal zodiac has drifted apart from the background stars of its namesake. The seasonal zodiac & sidereal zodiac currently have a 24 degree separation, but in another 10,000 years the two zodiacs will be completely inverted.
In other words, western astrology relies on a calendar & ephemeris to determine the placement of planets, but Vedic Astrology has been and always will be observable in the sky. (Btw, the term “astrology” means “that which relates to the stars”)
Gold Star Astrology
“Finding direction in the stars”