Astrology

What is sidereal astrology: Everything to know about the alternative zodiac

Get ready for your horoscope to change it’s scope.

For centuries, human beings have searched the stars to help them navigate the earth and understand themselves. Ancient Babylonians were among the first to record the constellations along the ecliptic, the path the sun appears to make through the sky. 

These OG astrologers recognized that different constellations would rise from the horizon line at sundown during different times of year.

Back to the future

The Babylonians, who already had a 12 month calendar based on the phases of the moon, assigned a constellation to each month. They applied myths, based on earlier Sumerian beliefs to these constellations and thus the zodiac wheel was born. Scholarship is divisive but it is generally understood that Egyptians refined the zodiac, and the Greeks cast it into the form we recognize today. The Greeks also gave it a proper name, ‘zodiac’ is derived from the Greek for “circle of animals.” These oracle heeding, robe loving folk borrowed myths from earlier iterations and added some of their own gods and heroes for good measure. Later, the Romans in their eternal imperialism, replaced the Greek names with Latin.

Babylonians were among the first to record the constellations that comprise the zodiac.
Getty Images

Tropical vs. sidereal

Astrologers use two primary zodiac systems to divine meaning from the cosmos; sidereal and tropical. In both tropical and sidereal systems, the zodiac wheel is divided into twelve signs. The primary difference between the two systems is where those signs are placed in the sky. The sidereal system is based on the current position of the constellations while the tropical system is based on where the stars were around 0 AD. In essence, the dates of the sidereal zodiac change over time and the dates of the tropical zodiac do not.

There was a time when the two systems aligned but they diverged around the year 285 AD; coincidentally, this was also the year that the Roman empire split into two factions and began its fated decline. From that point, due to conquest and colonization, and as we’ll explore a bit later, aversion to math, tropical astrology became the predominant system in the Western world. Sidereal meanwhile remained, and remains the governing system of Vedic astrology. Read more about Vedic astrology here.

Both tropical and sidereal astrology recognize the twelve signs of the zodiac.
Getty Images/iStockphoto

Same wheel, two ways

We can thank the mathematician Ptolemy for the static positioning of the tropical zodiac. He suggested that the vernal equinox, and thus the start of the zodiac be set at 0 degrees of the Aries constellation each year to ensure continuity between zodiac signs and the progression of seasons in the Northern Hemisphere.

Sidereal astrology, by comparison, is a touch more technical. Just as time marches on, children age and cities fall, so to do stars shift. Sidereal astrology recognizes that the earth sits on a skewed axis that contributes to the ever changing distances between earth and the constellations above, a movement know as the procession of the equinoxes which sounds like but is in fact not, the title of a George R.R. Martin book.

Both sidereal and tropical astrology divine meaning from the positioning of the celestial bodies at the time of birth.
Getty Images/iStockphoto

The deal with sidereal

To account for this procession, sidereal employs a corrective system of equations or ayanamsas to more precisely determine the current position of each zodiac sign. Part of the reason the tropical system is predominant is because humans are lazy and math is hard. The most widely used of these equations is the Lahiri ayanamsa. Under this corrective, the Sidereal Zodiac recognizes an apparent backward movement of fixed stars of about 1 degree every 72 years. Meaning there is a 24 degree gap between the tropical and sidereal systems, making them roughly an entire zodiac sign apart.

For as long humans have been looking up, we have been fixated on the motion of the stars we find there.
Getty Images/iStockphoto

Given the degree of discrepancy between tropical and sidereal systems, an individuals birth chart will vary according to which system is applied. While the dates of the respective zodiac signs are differ between systems, their qualities and influence are much the same. You can find your sidereal sign and birth chart using an online sidereal calculator like this.

Another important discrepancy between tropical and sidereal astrology is planetary rulership and influence. Unlike tropical astrology, sidereal astrology does not acknowledge the influence of Uranus, Neptune or Pluto on the individual or the individual’s birth chart. These outer planets are not visible to the naked eye and their distance from earth lessens their effect of life on it.


Astrology 101: Your guide to the stars


Is sidereal superior?

The validity of sidereal versus tropical is a subject of hot debate and as with all things, a matter of preference and resonance. The tropical system is not a true reflection of the present sky and its allegiance to seasons is fraught because they are inverted between the Northern and Southern hemisphere. In terms of sidereal astrology, even with calculated adjustments, the constellations do not line up exactly with their corresponding signs and thus the starting point of the zodiac is itself matter of constant contention.

At its most essential astrology is about observation, recognizing patterns and seeking understanding. As Morris Jastow writes of the Babylonians, “The theory upon which astrology rests is the assumption of a coordination between occurrences on earth and phenomena observed in the heavens… Astrology makes no attempt to turn the gods away from their purpose, but merely to determine a little in advance what they propose, so as to be prepared for coming events.” Whether you believe in one god or many or bow simply to the god that you are, astrology offers yet another reason to stare up and look ever forward.


Astrologer Reda Wigle researches and irreverently reports back on planetary configurations and their effect on each zodiac sign. Her horoscopes integrate history, poetry, pop culture and personal experience. She is also an accomplished writer who has profiled a variety of artists and performers, as well as extensively chronicled her experiences while traveling. Among the many intriguing topics she has tackled are cemetery etiquette, her love for dive bars, Cuban Airbnbs, a “girls guide” to strip clubs and the “weirdest” foods available abroad.