The difference between the tropical zodiac and the sidereal zodiac is rooted in the way they are calculated and the reference points they use:
Tropical Zodiac (or Western Astrology):
The tropical zodiac is based on the relationship between the Earth and the Sun.
It starts from the point where the Sun is at the vernal equinox and is therefore closely tied to the seasons. The vernal equinox is the moment when the center of the Sun crosses the plane of the Earth’s equator, moving from south to north.
Aries, the first sign in the tropical zodiac, begins at the vernal equinox.
Because the tropical zodiac is aligned with the equinoxes and solstices, it remains relatively stable over time.
The tropical zodiac is used predominantly in Western astrology.
Sidereal Zodiac (or Vedic Astrology):
The sidereal zodiac is based on the position of the stars.
It takes into account the precession of the equinoxes, a phenomenon where the Earth’s axis slowly rotates over a period of about 25,800 years. This precession causes the equinoxes to move backward through the zodiac signs.
The sidereal zodiac aligns its signs with their namesake constellations.
Due to the precession of the equinoxes, there is a gradual shift in the backdrop of fixed stars against which the equinoxes and solstices occur. This leads to an increasing difference between the tropical and sidereal zodiacs over time.
The sidereal zodiac is used predominantly in Vedic (Indian) astrology.
The Difference in Degrees:
The difference between the starting point of the tropical zodiac and the sidereal zodiac is called the “ayanamsa.” The ayanamsa value is currently around 24 degrees, meaning the two zodiacs are roughly 24 degrees apart.
For example, when the Sun is at 0 degrees Aries in the tropical zodiac, it is at approximately 6 degrees Pisces in the sidereal zodiac. This gap increases slowly over time due to the precession of the equinoxes.
This is why if someone is born with their Sun in Aries according to the tropical zodiac, they might find their Sun sign to be Pisces in the sidereal zodiac.
Why the Difference Matters:
Since the two zodiac systems are calculated differently and have different reference points, the position of planets in signs can differ significantly between them. This can lead to vastly different astrological interpretations.
For example, while someone’s tropical chart might indicate they are an assertive Aries, their sidereal chart might describe them as a dreamy Pisces. Both systems have their own merits and are used for different traditions and astrological practices.
In conclusion, while both zodiacs offer valuable insights, they approach the sky from different perspectives: one is season-based (tropical), and the other is star-based (sidereal). The choice of which to use often depends on cultural and traditional preferences.
