The REAL Difference Between Tropical and Sidereal
Clearing up misconceptions. The historical and mathematical differences.
I get this question all the time so I am finally answering it: what is the real difference between Sidereal and Tropical astrology? I will break this answer into three parts: the terminology, historical, and mathematical differences between the zodiacs.
First, let’s talk about terminology. Technically, the terms Sidereal or Tropical astrology are misnomers. Astrology refers to the act of studying the celestial bodies and the meaning made from their movement patterns. There are several different types of astrology such as Hellenistic, Vedic, Chinese (Bazi), Mayan, Egyptian, karmic, medical, electional, psychological, business, finance, synastry, mundane, political, etc. All of these different types of astrology are frameworks or strategies that are used to interpret the meanings of celestial bodies and their movements.
The terms Sidereal andTropical refer to the zodiac or mathematical calculation used to determine what celestial bodies are being studied and where in the sky those celestial bodies are at a given time. Zodiacs are often confused with frameworks because they originate from specific ethnic groups and typically are used with one or a select set of frameworks that was created around the same time and from the same people that specific zodiac was first calculated. For instance, the Tropical zodiac and Hellenistic framework (which are most often used together) both originate out of ancient Greko/Roman-ruled Egypt around the 1st century BCE. This is why the terms “Tropical astrology” and “Hellenistic astrology” are often used interchangeably. The Hellenistic framework is most often used with the Tropical zodiac. But many western Sidereal astrologers use this same Hellenistic framework and apply it to the Sidereal zodiac instead. We see this mixing and matching of frameworks with zodiacs throughout many different astrological traditions with varying degrees of universal acceptance. There is a very controversial Vedic astrologer who uses the Tropical zodiac for human events named Vic DiCara. He is controversial because it is the greater consensus within the Vedic tradition that the Tropical zodiac CANNOT be used in conjunction with the Vedic framework for predicting human events. However, he and his many loyal followers claim that it works for them.
Now that we know the right terminology to use when discussing differences in astrological practices, let's break down where these two zodiacs come from. The Sidereal zodiac was calculated first in pre-colonial Africa. However, at the time of its creation Africa was called Merita by its human inhabitants. Some modern historians have made the effort to trace the Sidereal zodiac’s origins back to ancient Kemet. Kemet is the indigenous name for Egypt, before Greece invaded and colonized it. However, we know today that Kemet was formed by the diverse indigenous people across the continent. The people of what we now call Sudan, Democratic Republic of the Congo, Ethiopia, and many other African countries took their religions, math, sciences, and literature and built Kemet and later Egypt into the great empire it once was. Because of this, we can assume that the true origins of the Sidereal zodiac were born from a collaborative effort of the whole of Merita. Before its fall, Kemet was considered to be the world epicenter for trade, wealth, and education. Scholars from all over Asia and eastern Europe would travel to Kemet to learn at the feet of African scholars. This is how astrology spread across the world, and how the Sidereal zodiac made it to ancient Babylonia (the place most credited by modern historians as the birthplace of astrology) and India where it became the centerpiece of the beautiful Jyotish (Vedic astrology) tradition.
After Greece invaded Kemet and renamed it Egypt, the astrological traditions, along with all other traditions were consequently appropriated and infused with Greko-Roman influence and culture. Out of this, the Hellenistic astrological framework was born along with the Tropical zodiac. This framework and zodiac later became the dominant form of practicing astrology in the Roman world, and to this day is still the most well known way of practicing in the parts of the world most affected by European colonization. There are several types of zodiacs outside of Tropical and Sidereal. This retelling is only the history of how these specific two came to be.
And finally, time for the mathematical differences between the Sidereal and Tropical zodiacs. The math is probably what is most discussed when it comes to the differences between these two. In my opinion though, the math doesn’t really matter if the history is not known, which is why that was discussed first. The Sidereal zodiac was created first, and the Tropical zodiac was created with Sidereal as the blueprint.
The Sidereal zodiac operates with the perspective that the stars in the sky are fixed and do not move, but the Earth itself is moving or rotating. Because of this, the Sidereal zodiac starts in the same place every year at 0° Aries. Depending on which ayanamsa you use, the Sidereal zodiac will start at a different place. But I use the Hindu/Lahiri ayanamsa, so every year the Sidereal zodiac calculation I use measures 0° Aries at exactly opposite or 180° from the star Spica in the Virgo constellation. Different ayanamsas will start the zodiac at a different star, but it is always the same fixed star every year.
The Tropical zodiac is calculated with the perspective that the Earth is fixed and does NOT move or rotate, but the stars or sky are moving. Instead of starting and measuring the zodiac against a fixed star system like Sidereal, the Tropical zodiac is measured against the equinoxes and tropical seasons on Earth. So instead of the Tropical zodiac starting at the same star every year, 0° Tropical Aries starts on the day of the Spring equinox every year. And thus 0° Cancer starts on the day of the summer solstice, 0° Libra starts on the fall equinox, and 0° Capricorn starts on the winter solstice. The equinoxes and solstices do not occur on the same day every year, so the Tropical zodiac must be RECALCULATED every year, whereas the Sidereal zodiac is not. When the Romans first created the Tropical zodiac, they did not know about the “precession of equinoxes.” This is “the slow, westward movement of the equinoxes along the ecliptic, or plane of Earth's orbit. This motion is caused by the Earth's axis of rotation.” Because of this, they were unaware that the Tropical zodiac would eventually have what is today a 24° difference from the Sidereal zodiac. Had we been born in ancient Egypt, our Tropical birth charts would be nearly identical to our Sidereal birth charts as these two zodiacs move apart 1° from each other roughly every 72 years.
Most historians agree that it was ancient Indian and Muslim astrologers who first realized the zodiacs were slowly moving away from each other, but didn’t know why. Then in the 2nd century the famous Roman astrologer Claudius Ptolemy “discovered” procession. However, many Vedic scholars argue that Indians already knew about procession, as this is the reason given for various ayanamsas in ancient Vedic texts that are about 2,500 years older than the Roman discovery. I’ll willingly admit I am biased, but given all of the highly advanced Kemetic knowledge that the Greeks and Romans were not educated enough to translate, it makes much more sense to me that the knowledge of precession was well known in the pre Greko-Roman world, and was lost during colonization.
Before we end, I must address a very big misconception about the mathematical differences between the Tropical and Sidereal zodiacs, and that is the notion that Sidereal is more accurate than Tropical because Sidereal shows where the planets actually are in the sky, whereas Tropical does not. This is not entirely true. While yes, if you follow any observatories or astronomers, when they speak about a planet being in a specific constellation, often it will align with where the Sidereal zodiac says that planet is. But both Sidereal and Tropical have one major flaw, and that is that they assume all 12 signs or constellations take up an equal 30° in the sky. They do not. Some constellations are way smaller than 30° and some are way larger than that. Both zodiacs at some point during every year will say a planet is somewhere it actually is not. If you are trying to decide which zodiac to use, mathematical accuracy is not a legitimate determining factor. Alternatively, I would consider the historical context of both zodiacs, as well as what various astrological frameworks have to say about them. Vedic astrology is a great framework to turn to for advice on this subject because it utilizes both zodiacs. Vedic astrology uses Sidereal for human related events and Tropical for non-human related events such as animals, plants, and the weather.
So, what do you think about the differences between Sidereal and Tropical? Which zodiac do you primarily use, and will you be changing after reading this? Why or why not? Let me know in the comments!
Check out my Tiktok How the Greeks Stole Astrology from Ancient Africans to learn more about the history of astrology!
To learn how to cast your Sidereal birth chart, click here.
Thank you for stopping by! Did you like this post? If so, check out my readings.
Tips
Venmo: astralotea
Cashap: $astralotea
Paypal: paypal.me/CWillis139
THIS IS SO FASCINATING!! i'm so curious about what it would look like to calculate based on the presumption that BOTH the Earth + the Stars are moving? This lines up more with the "precession of the ages" described in the Vedas, of the Yuga cycles, where there's a larger solar cycle that our whole solar system is moving through (alongside the movement of the Earth herself). This also explains why in "both" frameworks, there's moments of IMMENSE accuracy, and also times where the vibe is right but like... a few days off, or a week off, or something.
thank you for writing this! it's so concise and succinct.