Sidereal VS. Tropical Astrology
Knowing the placement of the stars at your birth can give you a lot of insight into the energy pattern/signature your soul carries and the purpose of your incarnation on Earth. This can be very important information when trying to decode psychological patterns and events that the universe creates for your soul's growth.
When approaching this topic it is important to understand that the astronomical placement of the stars can be calculated differently based on the Astrological System that is used. For example, most people know that being born between the dates of March 21 - April 20 makes their Sun Sign an Aries. However, in the Sidereal system, it might be calculated as Pisces.
There are a few different systems of calculating the stars’ positions at birth. I will be comparing and contrasting the Sidereal vs Tropical way.
Now let’s start with the most well-known and widely used in the Western world.
The Tropical system is a system that was implemented during the Hellenistic period in Europe and has since spread further west. This system operates on the basis of the Vernal Equinox. That means that every year on the first day of Spring the zodiac is calculated at 0 degrees Aries. This system follows the Sun's position along the ecliptic (an imaginary arc that the earth makes around the sun).
In the Tropical system, all of the constellations for each of the 12 zodiac signs intersect the ecliptic for 30 degrees each. However only a small portion of each constellation intersects, and the zodiac signs are only roughly based on the meanings assigned to their respective constellation. This system is based mainly on the seasons and the energy assigned to each. It can be compared to and is often overlapped with the Pagan Wheel of the Year.
In the Northern Hemisphere, Spring starts on March 20th/21st so the Vernal Equinox was chosen to represent the start of Aries’ Season which represents the rebirth of Spring. Cancer begins on the Summer Solstice, Libra on the Autumn Equinox, and Capricorn on the Winter Solstice. This is the way it has been for around 2,000 years, with the signs taking on the characteristics of each season. This is a very useful and easy-to-follow system that stays the same over time. What is interesting to note, however, is that at the beginning of the Tropical System's implementation, the astronomical constellations (stars) aligned exactly with the seasons, but over time something called the Precession of the Equinoxes occurred causing this to change.
The Precession of the Equinoxes describes the gradual shift in the orientation of the Earth's axis which produces the illusion of the celestial sphere moving backward. This precession slightly changes the position of the Sun at the Vernal Equinox each year. Every 72 years the position of the Sun moves back approximately one degree and a full 360-degree rotation occurs every 25,920 years. Over the course of about 2,000 years since the implementation of the Tropical system, it has moved back 24 degrees. This means that the astronomical position of the Sun on the Vernal Equinox today is not 0 degrees Aries, but approximately 6 degrees Pisces.
This is perhaps a complex theory for most to grasp because it requires a basic understanding of Astronomy, but to put it simply Tropical is based on the seasons, NOT the exact position of the stars and as a result, it has not moved to account for the shifting of the celestial sphere. Whereas Sidereal does account for precession and shifts gradually over time as explained in the next section. The Tropical system works well for many people, however, it does not tell the astronomical location of the planets - only the planets in relation to the equinoxes.
The Sidereal system is a system mainly used in the Eastern world by Vedic astrologers. Vedic Astrology, one of the main Astrological Systems utilizing the Sidereal calculation, is a type of astrology very richly steeped in Indian culture and history. In this article, we will be discussing the Sidereal calculation which can be implemented using Western or Eastern Astrology Systems.
The Sidereal system focuses on calculating the stars based on their position inside of the constellations. So the constellations that form the basis of the zodiac signs we all know are taken into consideration here. However, this system is not perfect. There are disputes as to what star in the constellation of Aries should mark the beginning of the zodiac (0 degrees Aries). There are different stars to use to calculate this but the most commonly used is the Lahiri ayanamsa.
As precession takes place, Vedic astrologers and those who use the Sidereal system keep track of the Astronomical placement of each planet inside of the constellations. Therefore keeping an accurate record of the Astronomical location of the planets within the constellations. The energy signatures of the planets can (in my opinion) be more easily felt this way as we are dealing with their exact locale. However, it is up to the individual to choose which system they would like to use to calculate their birth chart.
Both of these systems are well-functioning systems of calculating and interpreting birth charts, synastries, and other astrological calculations. However, the chart that is aligned more closely to modern-day Astronomy is the Sidereal system, because it focuses on the exact location of the stars as opposed to their seasonal relation.
It is important to note that the Tropical system carries significant relevance in the Northern hemisphere as the zodiac signs do follow the energy signatures of the four seasons.
Each system has significance in the modern world, in my experience, Sidereal connects more deeply with the passive or spiritual world, whereas Tropical follows the status quo being that it holds great meaning for the masses as a result of the collective belief in the system. Therefore giving Tropical a more dominant presence in the collective consciousness. I suggest using both systems and comparing until you find which one you feel more comfortable with.
Note that it can be difficult to find websites that support the Sidereal system because most astrology websites and platforms in the West operate using the Tropical system. However, many websites including masteringthezodiac.com and astro.com use the Sidereal system or have options to calculate such a chart. Just remember when using a site to calculate your chart, check “Sidereal” as the system you would like to operate with.
If Sidereal is not an option on the website, you can calculate your chart using the Tropical system and subtract 24 degrees from all of your house cusps and planetary placements. If a house cusp or planet is below 24 degrees of a sign it will move to the sign before it, so don’t be surprised if your entire chart shifts a bit. In most cases all of your aspects will pretty much be the same - only the signs and orbs may change slightly. Below you can find a chart of the dates for Sidereal Sun signs and Tropical Sun signs to compare.
(Chart property of Wikipedia)
I hope that was a comprehensive explanation of the difference between the two systems! If you have any questions feel free to let me know!
Burk, Kevin. “Tropical vs Sidereal.” The Real Astrology Academy, therealastrology.com/information/about-astrology/17-tropical-vs-sidereal.html.
Friedman, Hank. “The Vedic Signs.” Learn Astrology Free, 10 Dec. 2006, www.learnastrologyfree.com/vedicsigns.htm.
“Sidereal and Tropical Astrology.” Wikipedia, Wikimedia Foundation, 7 Jan. 2018, en.wikipedia.org/wiki/Sidereal_and_tropical_astrology.
Whitaker, Alex. “The Precession of The Equinoxes.” Ancient-Wisdom.com, www.ancient-wisdom.com/precession.htm.