Forem: iambox leekyuha

I Built a Free Korean Astrology Site — Tech Stack and Lessons

iambox leekyuha — Sat, 16 May 2026 16:19:23 +0000

Side project: built a free Korean Saju (4-pillar astrology) calculator. Sharing the tech stack and a few non-obvious gotchas.

Stack

Backend: Python 3.13, Flask
Hosting: PythonAnywhere free tier
Astronomy: Custom Meeus algorithm (no external library, 100s/day CPU limit)
No database: Charts are pure functions of input

Live site

https://tarofortune.pythonanywhere.com/en

Non-obvious lessons

1. Free tier CPU is precious

PythonAnywhere free tier gives 100 CPU seconds per day. Each Saju calculation iterates a Newton-style solver for solar term timing. Without caching, ~30 chart computations would burn through the limit.

from functools import lru_cache

@lru_cache(maxsize=4096)
def solar_term_jd(year: int, term_idx: int) -> float:
    # ...

Solar terms repeat for the same (year, term) pair, so caching is essentially free.

2. Korean text on Windows console is hell

Default code page on Windows is cp949. Add python -X utf8 script.py or os.environ["PYTHONIOENCODING"] = "utf-8" to avoid UnicodeEncodeError on every print of Korean characters.

3. PythonAnywhere whitelist for outbound HTTPS

Free tier blocks outgoing HTTPS except to whitelisted domains. Plan for this if your app needs to call external APIs.

4. i18n the right way

I added /en/ prefix routing rather than per-template translation logic. Cleaner separation, easier SEO with hreflang.

What's next

Multi-language expansion (Japanese, Chinese)
Service Worker for offline support (done)
IndexNow integration for instant Bing/Naver indexing (done)

Open to feedback on the math or UX. Try the chart reader and let me know what's off.

Day Master Theory: Why 60 Personality Archetypes Beat 12 Sun Signs

iambox leekyuha — Sat, 16 May 2026 12:17:04 +0000

Coming from Western astrology and curious about Asian systems? The biggest practical shift is resolution.

Sun signs: 12 archetypes

Day Pillars: 60 archetypes

In Korean Saju (and Chinese BaZi), your "core type" isn't your sun sign — it's your Day Pillar, the Heavenly Stem + Earthly Branch pair of your birth day. With 10 stems × 12 branches × parity-pairing, you get 60 distinct types.

Examples

A Western Leo could be one of these very different Day Pillars:

Bingwu (丙午) — fire + fire branch = maximum charisma
Renxu (壬戌) — water + earth branch = contemplative depth
Jiawu (甲午) — wood + fire branch = ambitious expressive

Same Sun, three different people.

How to find yours

Free calculator: https://tarofortune.pythonanywhere.com/en

Enter birth date and time. The site computes your Day Master (stem) and Day Pillar (stem-branch), then shows the archetype reading for that specific combination.

Why this matters for self-understanding

I'm not arguing Saju "predicts" anything. But as a vocabulary for self-reflection, 60 archetypes give you much more nuanced language than 12.

Same logic that makes MBTI's 16 types more useful than introvert/extravert binary.

What's your Day Pillar? Drop yours below.

Building a Saju (Korean Astrology) Calculator from Scratch in Python

iambox leekyuha — Sat, 16 May 2026 11:32:36 +0000

I built a free Korean astrology (Saju) calculator and wanted to share what makes the math interesting.

What's Saju?

Saju is the Korean tradition of Chinese 4-pillar astrology (BaZi). Your birth year, month, day, and hour each get encoded as a Heavenly Stem + Earthly Branch pair, giving you 8 characters that describe your "energetic signature."

The interesting parts

1. Solar terms via Meeus algorithm

The year boundary isn't January 1 — it's the solar term Ipchun (立春, ~Feb 4), the moment the sun reaches 315° ecliptic longitude. To compute this precisely, I implemented the Meeus astronomical algorithm:

def apparent_solar_longitude(jd):
    t = (jd - 2451545.0) / 36525.0
    l0 = (280.46646 + 36000.76983 * t + 0.0003032 * t * t) % 360
    m = math.radians((357.52911 + 35999.05029 * t - 0.0001537 * t * t) % 360)
    c = ((1.914602 - 0.004817 * t - 0.000014 * t * t) * math.sin(m)
         + (0.019993 - 0.000101 * t) * math.sin(2 * m)
         + 0.000289 * math.sin(3 * m))
    return (l0 + c) % 360

Then Newton-style iteration to find the exact JD when longitude crosses 315°.

2. Late-Zi hour rule

The day pillar transitions at 23:00 local time, not midnight. If you're born between 23:00 and 24:00, your day pillar rolls forward to the next day. Common bug in online calculators.

3. Sixty-pillar cycle (六十甲子)

Ten Heavenly Stems × Twelve Earthly Branches, but they pair only on matching parity (Yang-Yang or Yin-Yin), so you get LCM(10, 12) / 2 = 30 paired combos × 2 polarities = 60 pillars.

def get_pillar_index(stem, branch):
    for i in range(60):
        if i % 10 == stem and i % 12 == branch:
            return i

Try it

Free Saju reader →

No signup, no email. Pure Python on Flask, hosted on PythonAnywhere free tier.

Open to feedback on the math or interpretation logic.