The Fascinating World of Sidereal and Tropical Astrology

Astrology has been a subject of fascination for centuries, with its roots deeply ingrained in humanity's worship of heavenly bodies. From the Babylonians to the Chinese, from the Hellenistic to the Islamic civilizations, astrology has...

Astrology has been a subject of fascination for centuries, with its roots deeply ingrained in humanity's worship of heavenly bodies. From the Babylonians to the Chinese, from the Hellenistic to the Islamic civilizations, astrology has evolved and branched out into numerous traditions and systems. In this article, we will delve into the intriguing concepts of sidereal and tropical astrology and explore their fundamental differences.

Sidereal and Tropical Astrology: Two Different Perspectives

In the realm of astrology, the terms "sidereal" and "tropical" refer to two distinct systems of dividing the ecliptic into twelve signs. Each sign encompasses 30 degrees, resulting in a total of 360 degrees. These terms can also pertain to different definitions of a year, as applied in sidereal and tropical solar calendars.

Sidereal astrology calculates zodiac signs based on the observable sky, taking into account the apparent backward movement of fixed stars due to the Earth's axial precession. On the other hand, tropical astrology defines signs based on the seasons and considers 0 degrees of Aries as always coinciding with the March equinox.

These differing approaches have caused sidereal and tropical zodiac systems to gradually drift apart over the centuries. While they were aligned around 2,000 years ago, with the March equinox coinciding with Aries in the observable sky, they no longer share the same starting point today.

Precession of equinoxes Fig 1: The changing position of the vernal equinox over the course of about 25,800 years.

Sidereal Astrology: Accounting for Earth's Axial Precession

Sidereal astrology takes into consideration the Earth's axial precession, which causes the alignment between signs and constellations to shift over time. To maintain this alignment, sidereal astrology employs corrective systems known as ayanamsas. These systems ensure that the signs correspond to their respective constellations.

In Hindu astrology, the most widely used ayanamsa is the Lahiri ayanamsa, while Western sidereal astrology employs the Fagan-Bradley ayanamsa. These ayanamsa systems play a crucial role in accurately determining an individual's astrological sign based on their birth date.

Sidereal and tropical astrology Fig 2: The position of the equinoxes in relation to the zodiac signs.

Tropical Astrology: Anchored to the Seasons

In contrast to sidereal astrology, tropical astrology disregards the Earth's axial precession and bases its calculations on the seasonal cycle of the Northern Hemisphere. The zodiac signs remain the same in the Northern Hemisphere, although a small number of tropical astrologers adapt the zodiac to reflect seasons in the Southern Hemisphere.

However, it's worth noting that the majority of tropical astrologers consider the zodiac applicable to both hemispheres without modification. This means that the sign Aries always corresponds to the spring equinox, regardless of which hemisphere one is in.

Astronomic Zodiac: An Alternative Perspective

While the traditional zodiac considers the signs as equal divisions of the ecliptic, a small group of sidereal astrologers take a different approach. They define their signs based on the actual width of individual constellations and include constellations that are not part of the traditional zodiac.

For this purpose, the International Astronomical Union's constellation boundaries, established in 1930, are utilized. These boundaries determine the constellations in contact with the ecliptic. It's important to note that these boundaries were not defined with astrological purposes in mind.


Astrology encompasses a vast array of traditions, systems, and beliefs. Whether you adhere to sidereal or tropical astrology, or even explore the astronomic zodiac, astrology provides an intriguing lens through which we can perceive the world and our place within it. So, whether you consult your horoscope for guidance or simply marvel at the celestial wonders above, astrology will continue to captivate and inspire awe.


  • "The Primer of Sidereal Astrology," Cyril Fagan and Brigadier R. C. Firebrace
  • "The Real, Real Constellations of the Zodiac." John Mosley, Planetarian
  • "The Real Constellations of the Zodiac." Dr. Lee T. Shapiro, Planetarian
  • Raymond, Andrew. Secrets of the Sphinx Mysteries of the Ages Revealed
  • A History of Western Astrology, by S. Jim Tester

See Also:

  • Great year
  • Astrology and science
  • Synoptical astrology