> ## Documentation Index
> Fetch the complete documentation index at: https://docs.geometry.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Astro wheels

> Five sign systems in one payload — tropical, Vedic rasi, Fagan-Bradley, sidereal IAU, and true sidereal — with ecliptic degree spans so you can see why names diverge.

`get_card_for_birthdate` returns **five** Western/sidereal sign blocks under `astro_wheels`. They are **different systems**, not five copies of one answer. On many dates the names match; on others they diverge — that is expected.

## The five wheels

| Key in JSON                       | What it is                                                                                                                                | Signs |
| --------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- | ----- |
| [`tropical`](#tropical)           | Season-anchored (vernal equinox = 0°). Common “Western” magazine horoscope frame — **standard tropical**                                  | 12    |
| [`vedic_rasi`](#vedic-rasi)       | Vedic rāśi with **Lahiri**-style sidereal frame (+ nested nakshatra where returned)                                                       | 12    |
| [`fagan_bradley`](#fagan-bradley) | Western sidereal with **Fagan-Bradley** ayanamsa                                                                                          | 12    |
| [`sidereal_iau`](#sidereal-iau)   | IAU constellation boundaries along the ecliptic — **unequal spans** from real constellation sizes on the sky (includes **Ophiuchus**)     | 13    |
| [`sidereal_true`](#sidereal-true) | True sidereal wheel — **GEOMETRY’s preferred / recommended** 13-sign frame; **unequal spans** along the ecliptic (includes **Ophiuchus**) | 13    |

Always read **`sign_name`** (and `system_slug`) on the wheel you care about. Do not treat `sign_no` as a universal zodiac index — see [Field glossary](/field-glossary).

All five wheels ship in every birth-card payload. Tropical, Vedic, and Fagan-Bradley use equal 30° signs for seasons or tradition. **`sidereal_iau`** and **`sidereal_true`** use unequal widths that follow constellation position and size on the sky, including Ophiuchus. The cut lines differ; both try to reflect what is actually along the ecliptic. GEOMETRY recommends **`sidereal_true`** when you need a default — that is the wheel we use to reflect the sky as closely as we can. Use **`sidereal_iau`** for the IAU constellation map; use the equal-sign wheels when your users already expect those systems.

## Why the degrees differ

Each wheel assigns the Sun (and other bodies) to a sign by **ecliptic longitude**. The **degree tables** later on this page are the **sign boundaries** GEOMETRY uses, published in one shared **tropical-longitude frame** so you can compare them side by side.

| Wheel                             | How Aries is placed                                                                              | Span style                                             |
| --------------------------------- | ------------------------------------------------------------------------------------------------ | ------------------------------------------------------ |
| [`tropical`](#tropical)           | Aries starts at **0.00°** (equinox)                                                              | Equal **30°**                                          |
| [`vedic_rasi`](#vedic-rasi)       | Aries starts near **23.85°** (Lahiri at J2000, in this frame)                                    | Equal **30°**                                          |
| [`fagan_bradley`](#fagan-bradley) | Aries starts near **24.74°** (Fagan-Bradley at J2000)                                            | Equal **30°**                                          |
| [`sidereal_iau`](#sidereal-iau)   | Unequal IAU constellation cuts (Aries ≈ **28.83°**) — Delporte boundaries                        | Unequal; **Ophiuchus** between Scorpio and Sagittarius |
| [`sidereal_true`](#sidereal-true) | Unequal true-sidereal cuts (Aries **0.00°–19.50°** in this frame) — GEOMETRY recommended default | Unequal; **Ophiuchus** between Scorpio and Sagittarius |

Same calendar date → same Sun longitude → can land in different named signs when the **cuts** differ. That is the whole point of returning five wheels.

Membership rule: longitude λ is in a sign when `start ≤ λ < end`, with wrap-through **0°** for Pisces on the sidereal equal wheels and IAU (end \< start).

These boundaries are standard astronomical / traditional reference frames unified in our catalog — not a secret recipe.

## “Wrong sign” is usually the wrong wheel

If a newspaper or app says “Pisces” and `astro_wheels.sidereal_true.sign_name` says something else (or Ophiuchus), you are comparing **different cuts**, not catching a GEOMETRY bug.

**Self-check before filing anything:**

1. Which wheel does your source use (tropical vs Vedic vs Fagan-Bradley vs IAU vs true sidereal)?
2. Open the matching key under `astro_wheels` in the raw JSON.
3. Optionally compare the Sun’s tropical longitude for that date to the [degree tables](#degree-tables) below.
4. For sky dates (moon / season / retro), also read [Calendar boundaries](/calendar-boundaries) — GMT day vs local almanac is a separate class of “off by one.”

<h2 id="degree-tables">
  Degree tables
</h2>

Wheel order in the tables follows how Aries is placed in the shared tropical-longitude frame — equal 30° wheels first, then unequal IAU and true sidereal. Jump to a table:

1. [`tropical`](#tropical)
2. [`vedic_rasi`](#vedic-rasi)
3. [`fagan_bradley`](#fagan-bradley)
4. [`sidereal_iau`](#sidereal-iau)
5. [`sidereal_true`](#sidereal-true)

<h3 id="tropical">
  tropical (12)
</h3>

| Sign        | Start ° |  End ° | Span ° |
| ----------- | ------: | -----: | -----: |
| aries       |    0.00 |  30.00 |  30.00 |
| taurus      |   30.00 |  60.00 |  30.00 |
| gemini      |   60.00 |  90.00 |  30.00 |
| cancer      |   90.00 | 120.00 |  30.00 |
| leo         |  120.00 | 150.00 |  30.00 |
| virgo       |  150.00 | 180.00 |  30.00 |
| libra       |  180.00 | 210.00 |  30.00 |
| scorpio     |  210.00 | 240.00 |  30.00 |
| sagittarius |  240.00 | 270.00 |  30.00 |
| capricorn   |  270.00 | 300.00 |  30.00 |
| aquarius    |  300.00 | 330.00 |  30.00 |
| pisces      |  330.00 | 360.00 |  30.00 |

<h3 id="vedic-rasi">
  vedic\_rasi (12)
</h3>

| Sign        | Start ° |  End ° | Span ° |
| ----------- | ------: | -----: | -----: |
| aries       |   23.85 |  53.85 |  30.00 |
| taurus      |   53.85 |  83.85 |  30.00 |
| gemini      |   83.85 | 113.85 |  30.00 |
| cancer      |  113.85 | 143.85 |  30.00 |
| leo         |  143.85 | 173.85 |  30.00 |
| virgo       |  173.85 | 203.85 |  30.00 |
| libra       |  203.85 | 233.85 |  30.00 |
| scorpio     |  233.85 | 263.85 |  30.00 |
| sagittarius |  263.85 | 293.85 |  30.00 |
| capricorn   |  293.85 | 323.85 |  30.00 |
| aquarius    |  323.85 | 353.85 |  30.00 |
| pisces      |  353.85 |  23.85 |  30.00 |

<h3 id="fagan-bradley">
  fagan\_bradley (12)
</h3>

| Sign        | Start ° |  End ° | Span ° |
| ----------- | ------: | -----: | -----: |
| aries       |   24.74 |  54.74 |  30.00 |
| taurus      |   54.74 |  84.74 |  30.00 |
| gemini      |   84.74 | 114.74 |  30.00 |
| cancer      |  114.74 | 144.74 |  30.00 |
| leo         |  144.74 | 174.74 |  30.00 |
| virgo       |  174.74 | 204.74 |  30.00 |
| libra       |  204.74 | 234.74 |  30.00 |
| scorpio     |  234.74 | 264.74 |  30.00 |
| sagittarius |  264.74 | 294.74 |  30.00 |
| capricorn   |  294.74 | 324.74 |  30.00 |
| aquarius    |  324.74 | 354.74 |  30.00 |
| pisces      |  354.74 |  24.74 |  30.00 |

<h3 id="sidereal-iau">
  sidereal\_iau (13)
</h3>

| Sign          | Start ° |  End ° | Span ° |
| ------------- | ------: | -----: | -----: |
| aries         |   28.83 |  53.54 |  24.71 |
| taurus        |   53.54 |  90.40 |  36.86 |
| gemini        |   90.40 | 118.27 |  27.87 |
| cancer        |  118.27 | 138.83 |  20.56 |
| leo           |  138.83 | 173.85 |  35.02 |
| virgo         |  173.85 | 217.81 |  43.96 |
| libra         |  217.81 | 241.10 |  23.29 |
| scorpio       |  241.10 | 248.17 |   7.07 |
| **ophiuchus** |  248.17 | 266.59 |  18.42 |
| sagittarius   |  266.59 | 299.57 |  32.98 |
| capricorn     |  299.57 | 327.39 |  27.82 |
| aquarius      |  327.39 | 351.66 |  24.27 |
| pisces        |  351.66 |  28.83 |  37.17 |

<h3 id="sidereal-true">
  sidereal\_true (13) — preferred
</h3>

GEOMETRY’s recommended astrology default when you want a 13-sign true-sidereal reading.

| Sign          | Start ° |  End ° | Span ° |
| ------------- | ------: | -----: | -----: |
| aries         |    0.00 |  19.50 |  19.50 |
| taurus        |   19.50 |  56.50 |  37.00 |
| gemini        |   56.50 |  86.00 |  29.50 |
| cancer        |   86.00 | 103.00 |  17.00 |
| leo           |  103.00 | 141.50 |  38.50 |
| virgo         |  141.50 | 191.50 |  50.00 |
| libra         |  191.50 | 210.00 |  18.50 |
| scorpio       |  210.00 | 223.50 |  13.50 |
| **ophiuchus** |  223.50 | 236.00 |  12.50 |
| sagittarius   |  236.00 | 269.50 |  33.50 |
| capricorn     |  269.50 | 294.50 |  25.00 |
| aquarius      |  294.50 | 318.00 |  23.50 |
| pisces        |  318.00 | 360.00 |  42.00 |

## Coverage

All five wheels ship on the published **1900–2100** focus window. See [Data coverage](/coverage).