Tropical? Sidereal? What does it mean?
The most basic fundamentals to understand
Sometime around 2015 one of my friends introduced me to Vedic Astrology. Even though I was familiar with Indian culture and spirituality, even though I had taken a semester of Sanskrit in college, I didn’t even know that there was such a thing as Vedic Astrology. And then I learned that they used a different zodiac, called the “sidereal zodiac”. I didn’t know what that meant, but I assumed it must be better, that it must be the “true” zodiac. If I had gone down the path of studying astrology at that point I could have become a fanatic for sidereal…I would have been a fanatic who didn’t even understand what he was talking about it!
There are many issues that we can consider in relation to tropical and sidereal zodiacs, and, while everyone is certainly entitled to their opinion, I believe that the most basic qualification for participating in this discussion is know the fundamental ideas of how the zodiac is determined. If you can’t explain the general principles at issue, you shouldn’t enter into the debate you should continue reading this article and I will do my best to make it as clear as possible.
What is the zodiac?
In functional terms, the zodiac is a circle that goes around the Earth1.
From the perspective of Earth, the Sun and stars rotate around the Earth in a circle.
So, the zodiac is a circle, and the Sun and stars rotate around the Earth in a circle. Thus, the circle of the zodiac is related in some way to the rotation of the Sun and/or stars around the Earth.
Because a circle is infinite, the question “where does the circle start?" has no right answer. If we want to know where the circle of the zodiac starts, we have to choose a point.
There are four definite points in the circle that the Sun makes around the Earth: the northern solstice, when the Sun is northernmost in the sky, the southern solstice, when the Sun is southernmost in the sky, the ascending equinox, the midpoint between the southern solstice and the northern solstice, and the descending equinox, the midpoint between the northern solstice and the southern solstice.2
The tropical zodiac is defined thusly: the point of the ascending equinox is the point of 0° Aries. So, the moment of the ascending equinox is the moment when the Sun is at 0° Aries.
The sidereal zodiac is defined in relationship to some fixed star. Let’s take the True Chitra Paksha ayanamsha.3 With this definition of the zodiac, the star Spica is always at 0° Libra. So we find where the star Spica is at on the ecliptic, and that is where we place 0° Libra4.
The word “ayanamsha” basically means, “the point in the sky where we begin drawing the circle of the zodiac”. There are many ayanamshas in use, each defining a different starting point for the zodiac.
It is actually a misnomer to say “the sidereal zodiac”, unqualified, because there are actually many sidereal zodiacs depending on where you start drawing the circle.
Tropical means related to the motion of the Sun and the Earth. Sidereal means related to the stars.
Does this make sense? Any questions?
Yes, we know that in reality the Sun stays in place, and the Earth rotates around, but that isn’t obvious for us on Earth. So, right now, since the naive, and obvious, view of someone standing on Earth is that the Sun rotates around the Earth, that is how we will consider this issue.
for those of us in the northern hemisphere, we would usually say: winter solstice, summer solstice, spring equinox, fall equinox, respectively; opposite for the southern hemisphere. I want to avoid these terms because these issues are the same for both hemispheres, so I will use language that includes both hemispheres.
the most common ayanamsha, and the official one in India, is called Lahiri ayanamsha. according to Dieter Koch, Lahiri make a mistake in the calculations. his intention was for his ayanamsha to be what we now call True Citra Paksha ayanamsha
as i understand it, spica isn’t actually on the ecliptic, so you have to project it on to the ecliptic and then draw the circle from that point…but the idea is what we are going for here, not the details.