There is a weird truth about sidereal and tropical things. I call it “weird” only because it seems weird to many people, who have got the idea exactly backwards. The weird truth is this:

Tropical is precise.
Sidereal isn’t.

I’m talking about the numbers, the coordinates, not the interpretations. Yes, interpretations are based on coordinates so if the coordinates are imprecise, the interpretations are… Yes, yes. We can go there, but we shouldn’t. Not right now. We shouldn’t race ahead of ourselves. Those who put their right foot forward without being sure their left is on solid ground often tumble.

So, let’s focus on the relatively simple issue of accurate coordinates.

Why are tropical coordinates precise,
while sidereal coordinates are not?

Tropical coordinates are extremely precise because their borders are purely mathematical arcs, derived from idealization of the Moon’s average orbit. Being mathematical concepts at their very core, these borders cooperate perfectly with mathematical description. There is one important part of the tropical system that requires observation: timing the equinox (or solstice, if you prefer). Compared to math, observation is messy (प्रत्याक्षापाटव – “perception is awkward”), but this particular observation is relatively easy to do with relatively simple tools like hourglasses and water-pots. (The stress is on “relatively”. No scientific astronomical observation is “easy”.)

The entire sidereal system (properly used to define the stellar “nakshatra” zones) is based on observation, and the awkwardness of observation is exactly why its coordinates are relatively blurry. To define this system, we must observe a given star and measure the arc between it and a horizon or between it and another star, all of which are difficult to see, and which shimmer and shift in the air. This explains why there is small ambiguity in the measurements, and why arcs measured from one star don’t always tally exactly with arcs measured from a different one, which is in turn why people like you and I in 2023 are still faced with dozens and dozens of sidereal options to choose from, asking ourselves, “which ayanāṁśa is correct.”

How blurry is blurry? Not terribly. It is relatively easy to measure these stellar arcs fairly accurately, but very, very difficult to measure them with absolute precision. This is why the various definitions of sidereal space contradict each other only by one or two degrees, usually. However, even this small discrepancy becomes a nuance now and then, especially when we own or look at charts with things in the “blurry zones” – say, on one side of the Kṛttikā / Rohiṇī border according to one ayanāṁśa, but on the other side according to another.

In those cases, all we can really do is take a deep breath and either trust or rethink our decision to adopt whichever ayanamsha we previously decided to adopt. Rethinking risks constantly changing one’s opinion, because “grass” usually has “brown spots” on “either side of any fence.” So, I prefer to just rely on the sturdy and very reasonable concept that planets in border-degrees lose their certainty and therefore don’t really form the important “backbone” of interpretations. We can see their blurriness as part of their intended symbolism. We should therefore “look away” from these “blurry bits” and focus on the clear stuff elsewhere in the chart. The clear stuff will establish the clear backbone, and then the blurry bits will resolve themselves in response to that clarity.