The major difference between astrology and the observable astronomical constellations is due to the Precession of the Equinoxes. Astronomical Astrology takes into account the rotation, motion and orbits of the earth and planets to build a complete picture of the Galaxy at large.
You may ask, how does an equinox impact the position of the constellations? Equinox means “equal night”, being that time of year when all points on the Earth’s surface experience the same lengths of daylight and darkness. There are two equinoxes each year and the vernal equinox marks the point in time when the Sun crosses the celestial equator and is the beginning of spring in the northern hemisphere.
When Greek astronomer Hipparchus compiled his star catalogue in the year 129BC, he found that the positions of the stars did not match up with the older Babylonian observations. He observed that most of the stars and constellations had shifted a constant amount. This indicated to Hipparchus that it was not the stars themselves that had moved but the frame of reference, Earth, which had changed. Hipparchus concluded that the equinoxes were drifting westward along the ecliptic relative to the stars that were believed to be motionless from the perspective of astronomers, and opposite to the motion of the Sun along the ecliptic. The precession of the equinoxes is an ongoing process that has caused a shift in the position of the zodiac as seen from Earth.